Ok - so the light doesn't come on when the key is on and the rest of the dash is lit up like a Christmas tree. I've replaced the bulbs and did all the diagnostic testing based on the CD/DVD manual. The P/W wire has continuity to the switch and the switch has continuity to ground with the pedal down. The bulb and socket are good, and the ABS light works as it should. After finding all this I gave up. Next day I take off for work, and as I hit the key to start it, I see the brake warning light come on while it's cranking - then go off when it starts.

Is this pointing the finger at the cluster itself? Is there something else that could cause this symptom?

Thanks!

 

Start out by specifically identifying what you are working on, there are year to year differences.

 

My apologies-it's a 97 XLT extended can 5.4 4x4. It doesn't have daytime running lights and it was built 9/97. I'm pretty sure it does not have 4 wheel abs, only rear. Based on the troubleshooting I did, it seems like the p/w wire is not getting key on power, only when the starter is cranking.

Thanks for any help - this is a bit more complicated than my Model A

 

That's how it's supposed to work, see schematic in cell 62-005 in the EVTM. The BRAKE light is self-tested ONLY in START, it's separate from the self test for the rest of the bulbs.

The P/W wire is GROUNDED to turn on the bulb. The "high" side of the bulb is on the same circuit as the rest of the bulbs and is HOT IN START/RUN via fuse F29.

 

Ok - hmmmm. Then where does power come from for the key on activation of the light, or is the light only supposed to be on when cranking? Right now, that is the only time it comes on. It does not come one with just the key on or when the truck is running, even with the parking brake pedal depressed.

I really appreciate the help!

 

Did you fail look at the schematic? It shows when and how the light is supposed to come on.

If you have the factory service CD, you have the data.

That would indicate that either the switch isn't closing when the e-brake is set or the circuit between that switch and the P/W wire is open. See schematic.

Your cluster is fine in this regard, you have other issues.

 

I'll check it out when I get off work.

Thanks!

 

OK - Should I have key on power at the brake fluid level indicator connector(C162)? If I'm reading this right, the DG/V wire should be power on when cranking/run only, but the T/LG wire should be key on power, correct? If that's the case, then I have a break somewhere in that wire, because neither wire had power with the key on.

Thank You!

 

That depends on the state of multiple items.

If the ignition switch is in START, then no.
If the brake fluid switch is sensing low fluid, then no.
IF the RABS module has a serious fault, then no.

Only if none of the above are true as any of them will ground that point and cause a reading of zero volts.

This is a hard-wired logical OR-AND circuit.

The light is on (TRUE) when the following conditions are in effect :

The ignition switch is in RUN/START
.AND.
whenever any of the following is true:
If the ignition switch is in START.
If the brake fluid switch is sensing low fluid-
IF the RABS module has a serious fault.
The parking brake is set and the switch is working correctly.

If any of those conditions are true, then the low side of the bulb is "grounded" and the bulb comes on.

If all four conditions are FALSE, then the light is OFF.

So far EVERYTHING you've described is NORMAL operation. Why are you still wasting time on it?