Primus IQ Brake Controller Wiring Functions

Question

Question:

can you get me a wiring diagram for Primus IQ brake controller?

asked by: Dan

0

Expert Reply:

The Primus IQ # TK90160 doesn't have instructions that come with a wiring diagram, but we have a picture/diagram on our site that shows which wires are connected to which functions on your vehicle. I attached the diagram for you to view, the wires will be connected as follows:

White - Ground
Black - 12V Power
Blue - To 7-Way at rear of vehicle
Red - Cold side of stop light switch

If you are needing a new pigtail for your Primus IQ it is part # 7894. This same harness will work with most Tekonsha and Draw-Tite brake controllers.

expert reply by: Jon G

0

click to enlarge

Miles F.

2/26/2025

Thank you for providing the wiring picture diagram for the Primus IQ brake controller. Looking at the wiring picture diagram, please confirm if the "Ground (-) White" cable at the "Brake Control" going to the battery -ve terminal is purely the ground for the controller internal circuit (i.e. very low amp draw). If so: 1) Does this "Ground (-) White" cable need to be connected directly to the battery -ve terminal OR can it connect to a ground bus bar at the front of the vehicle?; 2) What should the cable AWG size be for this "Ground (-) White" cable from the brake controller if extra cable is required?; 3) If, therefore, the Ground cable from the trailer connector is for the Electric Brakes magnet circuit (as well as the lighting circuits) what should the cable AWG size be for this ground cable at the trailer and vehicle side of the 7-way connector? Thank you and bless you!

Jon G.

2/27/2025

@MilesF Either of those options will work. We always use 10 Gauge Wire # 10-1-1 for the ground. If you're needing to run both power and ground to the battery, then I recommend using the 2 Wire 10 Gauge Kit # 10-2-1 instead.

Miles F.

2/27/2025

@JonG Thank you Jon - GOD BLESS you for your help. ONE MORE question: With a motorhome, there is approximately 35-40 feet from the dash mounted electric brake controller to the trailer hitch hookup. What AWG should the +ve electric brake output cable extension be? is 10AWG also adequate for this cable purpose and length? THNAK YOU, Bless you!!

Jon G.

2/27/2025

@MilesF You can use lower gauge (thicker) wire if you want, but from our experience a brake controller can't put out more power than 10 Gauge can handle so using thicker wire wouldn't really give you any kind of advantage. Happy to help out!

Miles F.

3/10/2025

@JonG Hi Jon, ISSUE: Class A motorhome on a 2002/2003 Ford Chassis (which I think is a Ford E-550) WITHOUT a tow package configured for a trailer with electric brakes and how to connect the red “STOPLIGHT” cable on the Tekonsha Primus IQ harness. NOTE: I am an electrician with knowledge on 12v systems so your answer can be technical. The motorhome manual does not mention a tow package for a trailer with electric brakes and I cannot find any under dash plug for this). HOWEVER, there is a factory fitted trailer hitch 6 pin connector BUT only configured for trailer lighting. So I got the Tekonsha Primus IQ which comes with a harness with bare wires that allows me to wire in everything myself. I need to know what to splice the Tekonsha Primus IQ harness RED “STOPLIGHT” cable to - with THIS following issue: The Tekonsha Primus IQ brake controller box contained a warning leaflet which warns of older Fords where the brake pedal switch has a red with green stripe cable which is ONLY hot when the brake pedal is depressed AND when pedal is NOT depressed it goes directly to ground. It states that the red “STOPLIGHT” cable on the Tekonsha Primus IQ harness must NOT be connected to that red with green stripe cable as it will blow the brake controller when “Manual” control is selected. SO, it states to splice to the light green cable on the brake pedal switch instead. However, on this motorhome there is no red with green stripe cable. However, it DOES have the light green cable it states to use instead BUT this cable IS the one that is hot when the brake pedal is depressed, and WHEN pedal is not depressed it goes directly to ground. So surely I cannot use that light green cable suggested either for the same reason. There are 4 cables in total on the brake switch as follows: 1. The above mentioned light green cable: brake pedal depressed = HOT; brake pedal NOT depressed = directly to GROUND 2. Light green with red stripe: HOT all the time (obviously the 12v +ve cable to the switch). 3. Blue with black stripe: HOT all the time (possibly to do with cruise control?) 4. Black with blue stripe: GROUND all the time I then checked the motorhome hitch receptacle connector and discovered that the 2 pins dedicated to the stop (brake) lights are ALSO: brake pedal depressed = HOT; brake pedal NOT depressed = directly to GROUND. So what do I splice/connect the Primus IQ harness RED “STOPLIGHT” cable to where brake pedal depressed = HOT; brake pedal NOT depressed = OPEN CIRCUIT? I pray this all makes sense and that you have the miracle answer. Thank you for all your help.

Jon G.

3/11/2025

@MilesF Thanks for all the details! Long story short is that you can use any signal for that stop light switch as long as it only gets power when the brake pedal is pressed (and it obviously doesn't go to ground when not pressed). Motorhomes are weird because there are a handful of places brake controller wiring can be, and it seems like every motorhome is different. You can try checking under the dash, next to the steering column, and around your seat. If you aren't able to find anything then you'll want to look for a standalone stop light wire. If you still aren't able to find a wire that only shows the 12V power when pressing the brake pedal, then an alternative would be the Roadmaster Universal Stop Light Switch Kit # RM-751000 which makes its own stop light signal. This was designed for foreign vehicles where it's difficult to find the stop light switch, but it can be used on any vehicle really.

Helpful Links

tv-review-roadmaster-universal-stop-light-switch-kit-rm-751000.aspx

See All (8) Replies to Miles F. ∨

George

5/5/2025

In looking at this diagram, the black wire goes from the brake control to the positive battery and then from the positive battery to the trailer connector.I thought the power from the brake controller powered the brakes via the blue brake wire.

Jon G.

5/6/2025

@George Good question. Those are actually 2 different wires; one goes from the battery to the brake controller for power, and the other goes from the battery to the 7-Way connector for the 12V power. The blue wire from the brake controller will send out power from the controller out to the 7-Way and on to the trailer brakes like you mentioned.

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Primus IQ Brake Controller Wiring Functions

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