Troubleshooting No Trailer Brakes with Curt Spectrum Installed on 2018 GMC Sierra 1500

Updated 03/10/2020 | Published 03/09/2020

Products Featured in This Question

Curt Spectrum Trailer Brake Controller - Dash Mounted Knob - Up to 4 Axles - Proportional

(410)

$259.95

10 Gauge Wire - Blue Primary - Per Foot

(104)

$1.84

Deka Heat Shrink Butt Connector - 12-10 Gauge - Nylon Insulation - Yellow - Qty 5

(1104)

$8.26

LCD Digital Circuit Tester

(26)

$26.67

Question:

I have a 2018 GMC Sierra 1500. I bought the Curt 51170 in Dec. 2019 and just installed it 3/6/2020. using the GM supplied harness that came with the truck. After installing the control the knob is saying no trailer is connected. All the lites on the trailer are on so I assume my connection is good. Any idea as to why? Thanks for any help you can give me.

asked by: Joe

Expert Reply:

If the lights on your trailer are working but the Curt Spectrum Trailer Brake Controller # C51170 is telling you that a trailer isn't connected to your 2018 GMC Sierra 1500 then that means the problem is somewhere on your trailer brake circuit.

Try using a circuit tester # PTW2992 to test the pin in the 5 o'clock position on your truck-side 7-Way socket by applying full power to your trailer brakes. I would imagine that you will see a signal here since your pickup is newer but it would still be good to double check. If you aren't getting signal here then the wiring is damaged between your brake controller and the 7-Way socket and needs to be replaced.

If you do get signal on your truck side then the problem exists on your trailer side. This means that you will need to inspect your wiring from your 7-Way plug all the way to your trailer brakes, replacing anything that is damaged.

You can replace any damaged wiring (on your truck or trailer) with 10 Gauge Wire # 10-1-1 and Butt Connectors # DW05745-5.

Let me know if you're still having issues and I can help you troubleshoot further.