99 Silverado

[rjgti]

changed out the signal light switch now when you step on the brake the radio comes on and check engine light, almost like the key was in the run position. does not do it if the 4 way flashers are going. truck runs alright.

[bill190]

You may have got the wrong part???

 

In vehicles there are "diodes" installed to keep electricity from "back feeding" from one thing to another. Some electrical parts come with these diodes installed.

 

This is a *very* advanced troubleshooting problem which would require a factory wiring diagram and a lot of thinking...

 

BUT maybe if you still have the box the part came in, you could double check that the part you got was the correct part?

 

If you got it at a dealer, maybe you could go to another dealer and ask what part number you should have.

 

Or if from an auto parts store, go to another and ask what the part number should be.

 

Another possibility is a pinched or bare wire touching something due to the installation. Is this the turn signal switch mounted in the steering column?

 

Do you still have the old switch? Without dismantling the whole works, can you disconnect the new switch and connect the old switch (leave it hanging in air) and see if the problem goes away?

 

And then possibly do that with another replacement switch.