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Dj, ASE Certified Technician
Category: Toyota
Satisfied Customers: 1910
Experience:  ASE Master Tech, 30+ years in automotive repair.
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Sienna: My cruise control works until I turn on the head lights

Customer Question

My cruise control works until I turn on the head lights then the cruise control stops working
Submitted: 2 years ago.
Category: Toyota
Expert:  Dj replied 2 years ago.
Hello and thank you for trusting us with your question. I'm DJ. This could be a ground problem on one of the rear tail lights. When the tail lights come on, the controller for the cruise control thinks the brakes have been applied.You might be able to see one of the rear lights dimmer or acting strangely. If not, you'll have to dig a little deeper and check for voltage on the ground wire for the tail lights. First, check to see if any of the rear lights act strangely, like when you apply the brakes then the tail lights, does on go dim or dimmer than the other?Let me know and if we have to did deeper, you'll need a volt meter. Doesn't need to be an expensive one, even under ten bucks will work. DJ
Customer: replied 2 years ago.
When you mentioned the rear lights it dawned on me that I had installed tow hitch wiring that has a module that differentiates between the brake light and the tail light coming on when you press the brake. I noticed the panel lights and the radio lights coming on when I step on the brake. I could not figure it out until you mentioned the short in the tail lights. It turned out to be the little black box that came with the tow hitch light assembly. You might want to make notes on that problem in case some other dummy makes the same mistake that I did.
Expert:  Dj replied 2 years ago.
Hi, Harry,
Have you already replaced the black box and did it fix the problem?
Customer: replied 2 years ago.
I did not replace it I merely disconnected it and that fixed the problem.
Expert:  Dj replied 2 years ago.
That's a great find. Congratulations.