No brake lights when engine running

[mockspeed88]

So when I hit the brakes with the key off the hvac control comes on. The brakes go off momentarily then they if I hit the brakes again they light up

 

[mockspeed88]

I replaced the brake switch didn't do a thing

 

[mockspeed88]

Sparky's Answers - 1994 Chevrolet 1500 Pickup, Stoplights Will Not Work With The Ignition On

This 1994 Chevrolet K1500 pickup came in with the very unusual complaint that the stoplights would not work with the ignition on. I checked the brake light operation and sure enough the stoplights worked with the key off but as soon as the key was turned on they stopped. I did notice that the...

sparkys-answers.com

So I found this. My wipers do not work either and I just did the trans. I will check this ground in the morning when it is light out. Fingers crossed

 

[mockspeed88]

Fixed! Was the ground on the back of the pass cylinder head. It runs from the brake relay on the firewall to the wiper motor to a stud that is on the pass cylinder head. I now have brake lights and wipers! Thank you all for your assistance in helping me trouble shoot this

 

[HotWheelsBurban]

Fixed! Was the ground on the back of the pass cylinder head. It runs from the brake relay on the firewall to the wiper motor to a stud that is on the pass cylinder head. I now have brake lights and wipers! Thank you all for your assistance in helping me trouble shoot this

Glad you figured it out, and thanks for letting us know what it was. Someone else may need this information at some point; electrical problems happen to all old trucks eventually.

 

[Eveready]

Almost always when it is something both electrical and strange (like the AC control lights coming on ) it is going to turn out to be a ground somewhere. Congrats on tracking it down and let me repeat the previous thanks for coming back to the thread with the answer. It will happen again and a link to this one goes in my infamous truck file.

 

[GoToGuy]

The advantage to having " ganged up " grounds are effeciancy in assembly and diagnostics. The disadvantage is if one or more of the " ganged up " circuits isnt finding body, frame, battery ground it will look for another route not intended, with unknown results.