Cruise control stops working when the headlights are turned on

Hi,

The one thing I see as far as wiring is both circuits possess a common ground location. If you look under the dash on the left side, check for a black wire mounted on the body of the vehicle. If it is weak, corroded, loose, or damaged, it can be causing this simply because the ground can't handle the power surge.

Let me know if you are able to locate it and what is found.

Take care,

Joe

I found the ground behind every brake pedal and it's good, not loose or oxidized.

Hi,

Do me a favor. Have a helper apply the brakes on and off as you watch the taillights. Then turn the headlamps on and do the same. Does it appear the brake lights are already on without the pedal depressed?

Let me know.

Joe

No, looks like it should.

Hi,

At this point, it could be related to what is called the body control module (BCM). To determine if the module is related, it needs to be scanned to see if there are codes that are related to the problem. Otherwise, it becomes a guessing game.

In this case, the CAN bus needs to be scanned. CAN stands for controller area network. Basically, all the computers/modules are tied together via a few wires. This type of scan will identify if codes exist regardless of the module, it's stored in.

Here is a video showing what needs to be done:

https://youtu.be/u-4syLc-ifQ

Here is the thing. Basic scan tools like those used in most parts stores won't read these types of codes. If it's possible, this should be considered.

Let me know your thoughts.

Take care,

Joe

Trailer lights were tied into taillight harness was causing the problems, once they were disconnected from the harness everything was corrected. Thank you all very much for input.

Hi,

Thanks for the update. I'm glad to hear it's fixed. Was the trailer harness wired with an aftermarket unit?

If you can, let me know. If you're busy, I understand. I'm just glad it's working for you.

Take care and feel free to come back anytime in the future.

Joe