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Optronics Trailer Tail Light - Stop, Turn, Tail - Incandescent - Round - Red Lens

Optronics Trailer Tail Light - Stop, Turn, Tail - Incandescent - Round - Red Lens

Item # ST40RB
Our Price: $10.05
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Shipping Weight: 0.49 lbs
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5-3/8" Diameter round. Incandescent trailer light provides stop, turn, and tail signal. Shock-proof socket protects bulb against damage. Durable steel housing. Flush mount to trailer - hardware not included. 2-Wire design. (1) 2057 bulb. Great Prices for the best trailer lights from Optronics. Optronics Trailer Tail Light - Stop, Turn, Tail - Incandescent - Round - Red Lens part number ST40RB can be ordered online at or call 1-800-940-8924 for expert service.
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  • Reviews (120)
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Optronics Trailer Lights - ST40RB

  • Tail Lights
  • Round
  • Incandescent Light
  • Red
  • 5-3/8 Inch Diameter
  • Recessed Mount
  • Stop/Turn/Tail
  • Non-Submersible Lights
  • Optronics

5-3/8" Diameter round. Incandescent trailer light provides stop, turn, and tail signal. Shock-proof socket protects bulb against damage. Durable steel housing. Flush mount to trailer - hardware not included. 2-Wire design. (1) 2057 bulb.


  • Round incandescent trailer light serves 3 functions
    • Stop, turn, and tail
  • Shock-proof socket protects bulb against damage
  • Incandescent 2057 bulb can be easily replaced
  • Durable steel housing
  • Red acrylic lens over bulb
  • Compatible with 12V DC systems
  • Flush mount to trailer with flange - hardware not included
    • Requires cutout
  • 2-Wire design includes power lead and ground wire


  • Dimensions: 5-3/8" diameter x 1-9/16" thick
  • Bulb type: 2057
  • Power draw at 12.8V:
    • Stop/turn: 2.4 amps
    • Tail: 0.49 amps
  • 3-Year warranty

Manufacturer Cross Reference
Light will work as an exact replacement for:
Uni Bond # TL4300R
Truck Lite # 80334R
Grote # 50232
Peterson # 413/425

Optronics ST40 Series Tail Light Dimensions

ST40RB Optronics Trailer Tail Light - Stop, Turn, Tail - Incandescent - Round - Red Lens

Alternate part number: ST-40RB

California residents: click here

Customer Satisfaction Score:

Customer Reviews

Optronics Trailer Tail Light - Stop, Turn, Tail - Incandescent - Round - Red Lens - ST40RB

Average Customer Rating:  4.7 out of 5 stars   (120 Customer Reviews)

5-3/8" Diameter round. Incandescent trailer light provides stop, turn, and tail signal. Shock-proof socket protects bulb against damage. Durable steel housing. Flush mount to trailer - hardware not included. 2-Wire design. (1) 2057 bulb.


I wanted to change out the rear lights on my 1949 Chevy 3600.

This is a daily driver for me, not some show truck, so I wanted to protect the lights as well.

I started with a piece of 6” schedule 40 pipe. Then I cut a disk to mount the lights on with a hole saw and welded them in place.

I cut a slot into the bottom of the driver’s side light and milled a matching slot in the pipe. This was to allow light to shine down on the license plate.

Then a drilled and tapped #6-32 holes in the edge of the pipe so that I was able to screw the protective expanded mesh onto it.

Last, I primed and painted them up to match as close a possible.

Very happy with how it all turned out.



GREAT- Everybody love them.


this was a very easy install. the holes were already there to place the lights. I ran new wiring from the hitch all the way to the lights. I brought the wiring in near the circuit box up front and ran it in the cupboards to the rear. (it was easier to run new wires, the old ones were pieced together) I also was able to get the dents out and stablize the bottom of the wall. I would recomend redoing the wires when you do this. It saves a lot of headaches trying to figure where your wire may be bad. The old lights were big and boxy.

Lisa G.


what type of camper and year is that?

Patrick B.


We have sent an email to Mike and if he has anything to add, it will appear below his original review. Keep an eye on that page.

Lisa G.


This is to answer Lisa Gs question. the year is 1973 and the camper is a Serro Scotty

Patrick B.


Thanks for the follow up, and we hope the lights are serving well.


Very nice light. It flush mounts and is a easy install. I needed something of this type for my bantam trailer rebuild and these worked great



After a year of being submerged in creek crossings, surviving being beat on washboard and washed out roads the lights are still working great and bright as ever.


I often recommend Etrailer to people in my community of RV repair and Renewable Energy. I wish someone would do a video on how to replace hubs-wheels-bearings on older travel trailers with the Dayton-Dexter-Fayette Star wheels and include details on how to identify the axle and weight class. If you want to see what your products have been used on, heres an Example. I bet you never thought Etrailer would be the source for parts on a wind turbines pivot, shaft and furling parts!




Thank you very much perfect fit just like it was made for it. Do you know how can find out more about this trailer?

Etrailer Expert

Heather A.


It looks like an old livestock or horse trailer. The stamp on the back that says longhorn trailer company in Wichita falls, Texas closed in 2014. They were open for 68 years so its hard to tell how old it is.


Easy to install. Works well. Just like the original. I would buy again, if I need to.


Just perfect.


The Right Light at a GREAT PRICE! Easy to install and exactlly what was needed for my 1952 Stewart Coach. So glad I found your site and will continue buying all of my trailer needs with


Light was inexpensive but still well made. Easy to install - replaced the rusted out tail lights on my cattle trailer


Work great, easy to install.....4.5 inch hole saw does the trick.


Fit perfectly, nice look, great quality. Thank you


I purchased these to provide a look that I wanted on my 1954 1/2 ton flatbed.
I have only put 12 volts to them for test purposey to this point in time. I have been working on this project since 1999. It is now in it's final stages of construction as the body parts are now being painted. The, the lights, were placed in a 2x6 inch tube, on the end, to look like stop and turn lights on vehicles of that period in time, in the bumper. I went for the bulb look, not the l.e.d. for the look. Very happy with my choice.


Works perfect! Great price!


Perfect replacement for the tail lights on my old trash trailer. Mounted the lights and new wiring in an hour.


I purchased the Optronics Trailer Tail Light - Stop, Turn, Tail - Incandescent - Round - Red Lens for my camper. They were an exact match to the originals! Easy to order, great price, received quickly, easy to install, quality construction, just what I needed. Super service, I couldn't be more pleased or impressed with your company. A true pleasure doing business with you!


Installed the trailer lights and found problem with the outboard right light. The trailer has one light on the fender and two lights embedded in the tail cross piece. The problem was that when the running lights were on the outboard light was on the high side of the bulb and when grounded came on as a stop light. I spent several hours tracing wiring and got nowhere until I substituted an old square light and found that the problem went away. It seems that the pigtail that is in the bulb socket was installed with the low side in the high side hole and the notch matched up with the correct axis making the problem confusing and hard to detect. Although the bulb orientation was correct power application was not. Removed the wires and re-inserted them in the correct position and problem was rectified. Quality control problem? Otherwise great product at a great price


Just the right replacement fixture for my trailer and sent out promptly by the folks at etrailer. Thanks!

Scott S.


It still works great!


Product Review:I had these type lights on an old Toyota rust-bucket with a wooden bed which still is my most loveable vehicle; can't find these lights locally (N/W NC mountains); found your ad online and hoped these would match those already on the Toy and replace some damaged and rusty; couldn't believe I could get exact replacements, but I sure did; order date March 29 early AM, mailman handed them to me April 31 at 1 PM at my house "in the same year!" They had traveled, according to map, across from the edge of Missouri through the southern edge of Indiana, across the length E-W of Kentucky, SW Virginia to Greensboro, NC, then backtracked on land back to my home via USPS to me. Put them to your ear and you could still hear the Mississippi!!

Give it a big 5 stars!


Didn't notice the snap ring. Very convenient if used on a trailer but not what i wanted for my golf cart. Although they did fit in it perfectly i won't use them on the cart. Trading them out with my car hauler. Same size. Nice lights though.


I have been building trailers and truck beds for a while. I really like using the flange mount vs the rubber gasket and you can replace the bulb instead of a new light assembly.


Tail lights work great. Everything was included that needed to be. Used them on two old trailers, making them more visible and legal. Fast service. Great price.


Every item works fine! Parts were delivered in a timely fashion. Installation went well on a 25 yr old trailer. Thanks for being a source for repair parts on this older equipment!


Simple, classic, GREAT replacement for old cracked lens on 1969 Nomad. Will post a pic when I install. Super simple wires should make this a very easy install. I like the recessed lens as well as the snap ring which holds it back in the black metal case. Makes for great protection of lens and easy bulb replacement in the future.


The groove for the retaining ring is virtually nonexistent. Tap or jiggle it a little bit and the ring pops out and then the lens. I had to apply a couple dots of clear caulk around the lense and ring to keep them in place. But it works for a $5 taillight.

Show More Reviews

See what our Experts say about this Optronics Trailer Lights

  • 4 Inch Round Trailer Tail Light Cutout Size
    The closest to 4 inch round lights we have is the Optronics LED Trailer Utility Light # BUL43CB or Trailer tail Light # STL55RB which are actually 4-5/16" diameter x 1-15/16" thick. These are designed to fit the Rubber Grommet for 4" Round Trailer Lights - PVC # A45GB which requires a 4-1/2 inch diameter cutout. You will also need wiring pigtail # A47PB. If you are interested in the Optronics Trailer Tail Light - Stop, Turn, Tail - Incandescent - Round - Red Lens # ST40RB you asked from...
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  • Reverse Lights Illuminate With Running Lights On In Vehicle
    If the reverse lights on the trailer are on while the running lights in the vehicle are activated you most likely have a short between the reverse light wire (usually purple) and the running light wire (usually brown) on the trailer. Therefore, you will need to trace each of these wires back from the trailer side connector to make sure they have not shorted out to one another. I also recommend that you check the pins inside the trailer side connector for corrosion. Please note, aluminum...
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  • Comparing Optronics # ST40RB and Optronics # STL003RFLB Trailer Lights
    Aside from the Optronics # ST40RB having an incandescent bulb and the Optronics # STL003RFLB being LED the only other big difference is that the first part grounds through the mounting hardware while the LED version grounds through a wire. This is why one unit has 2 wires and the other has 3. We have 2 pigtail options for the LED verison for you to use. Part # A45PB has the wires coming straight out of the plug while part # A47PB has a right angle for tight spacing where your lights mount. I...
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  • Magnetic Flat Towing Tow Bar Wiring Kit Flashes Both Turn Signals Instead of Just One
    On a 7-Way, just as a 4-Way, the turn signals and brake lights are combined on the same circuit on each side. So yellow is left turn and brake, green is right turn and brake, brown is running lights, and white is ground. Usually when there is a red wire it is brake lights. But on a combined system like this the brake lights should be combined with the turn signals. There could be a short that is causing both turn signals to activate at the same time. You will want to inspect the wiring...
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  • With Trailer Connected Truck Reverse Lights and Trailer Brake Lights Are Not Working
    It sounds like you might have a few different issues going on here. First, we need to test the vehicle side 7-Way connector to make sure it is working properly. Use a circuit tester such as # PTW2991 to test the pins on the connector while someone sits in the truck and runs through the light functions. If something does not work then you will need to determine the problem. Check the trailer connector for corrosion inside and out. Corrosion can cause all sorts of issues, so can ground...
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  • Which Wires Serve What Function on Optronics Light ST40RB
    The green wire is for the brakes and turn signals and the black wire is for the tail lights .
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  • Troubleshooting the Brake Light Function of the Optronics Round Trailer Light part # ST40RB
    The Round Trailer Stop, Turn and Tail Light # ST40RB that you referenced grounds through the mounting hardware. A weak ground could definitely cause the brighter illumination of the # ST40RB to not function. I would make sure that this light is installed on a clean metal surface that touches the frame of your trailer. If not, you could run a jumper wire from the mounting hardware of the light to the frame of your trailer to improve the light's grounding. You could also test the assembly...
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  • Replacement LED Trailer Light to Reduce Power Draw
    The Optronics LED Trailer Light # STL42RB is not what I could call an exact replacement for the # ST40RB but for all purposes it will be what you're looking for. The # STL42RB is 1/8 inches larger in diameter and 3/8 inches deeper so at the most you may need to do a little filing to the opening for the light in your trailer to install it. The mounting flange is metal. There is also a Stainless Steel Trim Ring # A5TRSSB available. It does not include a gasket, however If you would prefer...
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  • Troubleshooting Running Lights Circuit on a Travel Trailer Tail Light Harness
    Since you have tested the 4-Way connector on your vehicle and it is working properly, it leads me to believe that the wiring of the lights is incorrect. You will want to make sure that the fuse for the running lights on the vehicle is not blown. It sounds to me like the lights you have only have two wires coming out of the back for wiring to the trailer connectors wiring. If this is the case then the red wire will connect to the yellow (left) and green (right) wires on the trailer lights....
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  • Wiring Instructions for Optronics 4-1/2 Inch Round Trailer Stop Turn and Tail Light # ST40RB
    Thanks again for ordering with, we appreciate your business. As for the ground, you are correct, the light housing on the Optronics 4-1/2 Inch Round Trailer Stop, Turn, and Tail Light, # ST40RB, doubles as the ground. Now for the green and black wire, the green wire is for the running light circuit and the black wire is for the turn signal and brake light circuit. I have attached a short installation video for you.
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  • Power is Getting to the Trailer Lights But they Will Not Light Up
    Use your circuit tester to test the wiring directly at the back of the lights. If the power is not getting to that point then there is a wiring issue that you will need to track down and repair. If power is getting to the light and the light is not coming on then the issue is either a weak or bad ground or there is something wrong with the light. The ground needs to be attached to a clean and corrosion free bare metal surface. Try moving the ground to a different location or run a jumper...
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  • Trailer Running Lights Do Not Work Using Tail Light # ST40RB
    It does sound like a ground problem. Use a circuit tester such as # PTW2993 if you do not already have one to test the running light wire at the back of taillight # ST40RB. If there is no power at the running light wire, then the issue is not at the light but further up on the trailer or tow vehicle. If there is power to the wire then the issue is most likely that the circuit is not being completed because of a bad ground. This tail light grounds through the mounting hardware so it will...
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  • Installation of Tail Light Lens Using Retainer Snap Ring
    The Replacement Tail Light Lens # A40RB is not held on with screws. The outer bezel housing of the 4-1/2" Round Trailer Stop, Turn and Tail Light, Flange Mount, 3-Function # ST40RB for instance has the housing held by screws and the lens is held by the metal snap/retainer ring and indentation in the housing. That Replacement Retainer Ring # 410-21 is a separate item.
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  • Troubleshooting No Trailer Running Lights
    I would begin by testing the trailer connector on the vehicle to rule that out. Turn the headlights on and use a circuit tester like part # PTW2993 to test the socket on the connector fed by the brown wire. If you are not getting a signal on this pin, you might have a blown fuse. Make sure the ground wire from the connector on the trailer is securely grounded to the trailer frame and that each lamp is grounded to the trailer frame either by an individual ground wire connected to the trailer...
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  • Optronics Trailer Tail Light Replacement Lens Clip
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  • Trailer Clearance Lights Show Power but Some Will Not Light Up
    It is possible that the clearance lights are not working if you have a lot of clearance lights. This can overload the trailer wiring on the vehicle side and cause some of the lights not to work. You can check the amperage draw per clearance light by testing one at a time using a multimeter such as # PT89ZR. Switching everything over to LEDs will be much better because they draw only a fraction of the power compared to incandescents. Another possibility is a poor ground connection. All...
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  • How to Remove Tail Light That Has Rivets Holding the Grommet in Place
    It all depends on how the light installs. If it is like the Optronics part # ST45RB that installs with the grommet # A45GB then you should be able to remove it without removing the grommet. You may need access behind the light to do this though. If your tail light is more like the Optronics part # ST40RB though where the grommet is part of the light then you will need to remove the rivets by drilling them out and then use new rivets or even screws to install the new tail light (or the...
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  • How to Determine the Functions of the Trailer Wiring on a Triton Trailer
    Most likely the white is ground, the brown is tail lights, the green is right turn/brake and the red is left turn/brake, but since the colors are a little different than the standard I would recommend you wire the trailer by function instead of color. This way you will eliminate and guess work and you will know that your trailer is wired correctly. The easiest way to do this would be to get a car battery and use a jumper cable to put current on each wire to see what tail light functions...
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    I do have an option for you but as we do not carry the trailer tail lights that you have, we would not have the correct replacement lens for you. That said, I can only imagine you will have a hard time trying to find an exact replacement as replacement lenses for old trailer lights are pretty hard to come by. Therefore, I recommend you replace the entire light as this is really your best option, the Optronics Trailer Tail Light part # ST40RB is very cost effective and is easy to install...
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  • Looking for 2-1/2 to 3 Inch Clear Round Trailer Light
    It depends on what type of light you are looking for. If you want a tail light assembly then it would have to have a red reflector on it to be DOT approved. If you are looking for a utility light (white light) then we do have some available, # UCL60CB or # UCL50CB. As far as just a lens we have some clear ones but they are over 4 inches in diameter.
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  • Trailer Back-Up Alarm Sounding when Brakes are Applied
    The back up alarm feed should be tapped into your reverse lamp lead, it sounds as if it is wired incorrectly. Each turn/brake lamp can be wired in series with a feed from your junction box, with one feed for the drivers side and another for the passenger. The same goes for your running lamps. You would take the feed for the drivers side brake/directional lamp which is usually a yellow wire, and run it along the rear of the trailer, feeding each of the two directional/brake lamps as you...
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  • What is the Difference Between a Snap Ring and Retainer Ring for a Trailer Tail Light
    There really isn't a difference. Snap-ring and retaining ring such as # 410-21 are two names for the same thing. If your tail light looks like # ST40RB then use # A40SRB. But you mentioned that the light was 4 inches, which is what Peterson light # 429800 is. So for that light use # 410-21. Shipping can vary depending on the option you choose and where you live. So take a look at the link to the right that explains more about shipping and how to determine cost.
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  • Power is Getting to Trailer Light but the Light Will Not Light Up
    There are a couple of things that you can check to see what the problem is with your trailer light. Since you mentioned that power is getting to the light it could be that the circuit is not being completed meaning a bad or weak ground connection. Light # ST40RB grounds through its mounting hardware. The attachment point must be clean and corrosion free. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding...
    view full answer...
  • Replacement Red and Clear Trailer Light Lenses for Peterson Lights
    We have a wide range of replacement trailer light lenses for Peterson and many other brands of popular trailer lighting. The linked page will let you select the shape of the lenses you need. If you know the brand of light you have, such as Peterson, you can also click on that filter to narrow the results shown. For examples, for a clear lens for a Peterson 413S stainless trailer tail light we have part # 414-15C. Part # 420-15 is a replacement red lens for a Peterson model 428S trailer...
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Employee Jameson C
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Employee Adam R
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Employee Kathleen M
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Employee Cole B
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