When is a Brake Light Relay # RM-88400 Needed and How to Wire One in 2007 Chevy Cobalt

Updated 01/12/2015 | Published 01/10/2015

Question:

I installed the Hopkins HM56100 tail light wiring system on my 2007 Chev. Cobalt Coupe. The Hopkins indicates that it has integrated diodes to prevent feedback from the RV. Based on other info I bought the RM-88400 Brake light relay kit. FIRST - do I need the brake light relay kit with the Hopkins Tail Light Wiring Kit? SECOND - assuming I do need it, I have been working on installing the relay on my Cobalt and IF it is needed, I have a wiring question - the brake light switch has 5 wires coming from it - a purple and a pink that have no 12V when the brake pedal is pushed or not, so I have determined they are not used. The other wires on the brake switch - a red with white stripe has 12v all the time, so not to be used. There are also 2 TWO light blue wires that both have 12V only when the brake pedal IS pushed. The instructions indicate to use the 1 ONE wire from the brake switch to hook the relay into. SO, WHICH BLUE WIRE DO I HOOK IT TO? Or, does it matter, or is this even the correct wire? Photo of all 5 wires included.

asked by: Bruce

Expert Reply:

Thank you for your multiple recent purchases from etrailer. We appreciate your confidence in us and your repeat business. Thank you also for your included photo.

There is a straightforward question/answer process to let you determine if a brake light relay is required for any particular flat-towing application:

Are you using a supplemental braking system that depresses the brake pedal in your towed car?
No - You do not need a brake light relay.
Yes - You may need a brake light relay. Continue on to the next question.

Do the brake lights on your towed car illuminate while the engine is off?
No - You do not need a brake light relay.
Yes - You may need a brake light relay. Continue on to the next question.

Do your towed car's brake lights act as both the brake signals and the turn signals?
No - You may need a brake light relay. Continue on to the next question.
Yes - Your towed car has a combined lighting system. You will need a brake light relay to ensure proper activation of its signal lights.

Does your towed car have separate brake lights and turn signals?
No - Your towed car has a combined lighting system. You will need a brake light relay.
Yes - Your towed car has a separate lighting system. You may need a brake light relay. Continue on to the next question.

Are you wiring your vehicle with a six-diode kit or a TowDaddy custom wiring harness?
No - You will need a brake light relay to ensure proper activation of your towed car's signal lights.
Yes - You do not need a brake light relay.

In terms of your second question about which brake light switch wire to use (thank you for the detailed information) you can use either of those blue wires that carries voltage ONLY when the brake pedal is pressed.