I have a 98 sierra with a 5.0 that I swapped a harness into from a 98 Tahoe with a 5.7 everything works other than the brake lights and the cab brake light stays on all the time I found a post about the orange wire having power and it needing to give the power to the white wire when u press the pedal but my white wire always has power aswell and no brake lights has anyone ever figured this out I’ve been thru every post I can find and there is no answer thanks in advance
Greetings cammiller277,
In the not too distant past we dug into a 'no brake light' issue for another member, and eventually
we teased out how the circuit actually works.
DISCLAIMER: That thread was for a '91, and from researching that I know that (I think) the '88-93 models
use one brake switch part number, while the '94-'99 models have a different one listed. As of now, I'm not
up to speed on the differences, but I'm sure that there are others who know this off the top of their head.
Anyway, in order to get yourself up to speed on all this, I'd recommend that you do the following:
1) Read through the other brake light thread, just to get a feel for how the General implemented the
brake lights. And also learn some of the unique lingo. (For example, I could never find 'brake light switch'
in the book. Instead, it is called the 'Stoplamp/TCC switch'.) And one switch closes when the brake pedal
is depressed, while the other switch *opens*. This seems to create a bit of confusion while troubleshooting.
(
'91 Brake Lights no worky thread)
Also, on your vehicle the center mounted brake light above the cab's rear window is driven directly from a relay located in
your Underhood Fuse block, so your newer truck will differ from the '91 there as well.
2) Now go over
HERE to the '98-specific FSMs and download them for the right price. What you want to do is
to find this same Stoplamp/TCC circuit in the '98 manual and piece it all together. No doubt there will be minor
differences in implementation, but once you have all this pieced together you will have exactly what you need
in order to get this circuit to work.
And if you have any questions during all this just post them and we'll work with you in the '98 manuals to
help figure out where the wiring error occurred. I know that I just gave you a starting point instead of
a direct answer, but to be honest the above is the best I can do at the moment...but at the same time this
felt better than just ignoring your question.
****
That was the long answer. The short answer?
With all of us researching this in the '98 FSM I have no doubt that we can get this brake light issue fully sorted out
in relatively short order. Using the FSM, no mysteries, just a little bit of a learning curve until you understand
the General's way of documenting this electrical stuff. :0)
Best of luck. Let us know what you discover --
