brake light problem

viggy58 · 02-08-2011, 12:11 PM

2000 chevy s10, 4.3L 2wd automatic.

all lights are working except the brake lights at the rear. The single brake light on the top of cab is working normally. when you step on the brake pedal, the cab mounted brake light illuminates, but the rears do not.

turn signals, taillights, and hazards all work normally. can't seem to find the problem. any ideas?

old_master · 02-08-2011, 02:26 PM

If the white wire at the multifunction switch shows battery voltage when the brakes are applied, the problem is in the multifunction switch. This thread shows how to clean the contacts: http://www.automotiveforums.com/vbul...d.php?t=577320 If that doesn't cure the problem, you'll need a new multifunction switch.

viggy58 · 02-09-2011, 02:28 AM

thanks for the reply. i'll be doing that tomorrow.

in the meantime, my friend decided that brake lights were more important than turn signals, so i cut off the "high side" wire from the bulbs, and spliced it to the light blue wire that is near the harness @ the rear drivers side bumper.

the light blue wire comes from the cab brake light (directly off the brake switch).

viggy58 · 02-09-2011, 02:22 PM

just took the multi function switch apart and cleaned it. didn't fix it. any other ideas?

replaced the brake signal switch at the pedal, that didnt fix it.
on the ignition switch, i checed for voltage at the white wire, didnt want to cut and splice, but i assume it is at the space #3, as it is the 3rd wire. unless things cris-cross inside the switch.
no voltage on that terminal, but the terminal associated with the orange wire (#2) is showing battery voltage at all times

old_master · 02-09-2011, 04:22 PM

Provided the white wire at the multifunction switch has battery voltage with the brakes applied, the next step is see if the voltage is going through the multifunction switch.

At the multifunction switch connector:

The yellow with black stripe wire and the dark green with white stripe wire must show battery voltage when the brakes are applied. If not, the switch is faulty.

viggy58 · 02-09-2011, 04:29 PM

i wasn't seeing battery voltage at any time on the white wire. the orange was always hot.

i'm gonna assume the switch is bad. the same time the brake lights went out, the horn stopped working. thanks for the advice. we're gonna be ordering a new multi-switch tonight.

on a side not. i'm pretty surprised with how relatively easy it is the get to and remove that switch.

old_master · 02-09-2011, 04:37 PM

Hold off on ordering that multifunction switch untill you know what the problem is.

If the high mount stop lamp works, it means the stop lamp switch is working. There are two white wires at the stop lamp switch, one goes to the high mount stop lamp and the other goes to the multifunction switch. If you're not getting voltage on the white wire at the multifunction switch with the brakes applied, the multifunction switch is NOT the problem. Look for an open circuit in the white wire from the stop lamp switch to the multifunction switch.

Rick Norwood · 02-09-2011, 09:23 PM

Quote:

Originally Posted by viggy58

i wasn't seeing battery voltage at any time on the white wire. the orange was always hot.

i'm gonna assume the switch is bad. the same time the brake lights went out, the horn stopped working. thanks for the advice. we're gonna be ordering a new multi-switch tonight.

on a side not. i'm pretty surprised with how relatively easy it is the get to and remove that switch.

Check to make sure your wires and connectors are all good and tight. A little squeeze at the terminal clips can help.

I almost threw $300 away on a Fuse panel because of a burnt wire connector that cost nothing to fix.

Check your wires with an Ohm meter for continuity.

Throwing parts at a problem is not good and Multifunction switches aren't cheap.

viggy58 · 02-11-2011, 03:28 AM

so, i'm gonna dive back into this tomorrow...

i just want to be sure of a few things:
the white wire you speak of, i should see battery voltage with the pedal off, but no voltage with the pedal pressed? Which white wire is it? the red or balck arrow in the pic? Also, if it is the black arrow, is that the same as the terminal with the yellow arrow? i was checking for voltage at the yellow arrow (trying not to cut into wires unless i have to) and had zero volts at all times.

thanks again for all the help. i'll be putting a hitch on this thing, once the lights are sorted out, and ill be sure to write up a "how-to"

old_master · 02-11-2011, 06:09 AM

The white wire must show battery voltage when you push on the brake pedal, and no voltage when you take your foot off of the brake pedal. Check those wires carefully, make sure it is white only, no stripe of any other color, plain white. According to the schematic, there's only one white wire to the multifunction switch.

viggy58 · 02-11-2011, 11:19 AM

no voltage on the white wire at the multifunction switch.. assuming i have the right wire

here's what my brake switch looks like...

one white, orange, 2 purple, brown, green, and green
which one would be the wire for the rear brake lights?

old_master · 02-11-2011, 04:07 PM

There are 6 terminals in your stop lamp switch connector, which does not correspond with the schematic. Please post your 17 character VIN, (Vehicle Identification Number) and the wire colors in the connector. If a wire has a stripe, include the color of the srtipe.

At the stop lamp switch: the orange wire should show battery voltage at all times. The white wire should show battery voltage when you step on the brake pedal. (If the high mount stop lamp works, it indicates that the white wire is getting voltage when you step on the brake pedal.) The other white wire goes to the multifunction switch, (for the stop lamps in the rear) and should also show battery voltage when you step on the brake pedal. The multifunction switch splits the signal for the rear brake lights.

viggy58 · 02-11-2011, 07:44 PM

i dont have access to the vin right now, its a friends truck and he had to drive it home. it's a 2001 gmc sonoma. 4.3L auto trans. extended cab.

see, at the stop light switch i have wires in this order (as seen in the pic):

white, orange, 2 purple on 1 terminal, brown, lt green, dark green.

no stripes on any of them.

the orange and white wires are working as they are supposed too at the brake switch.

on the multifunction switch, i have 2 white wires. i guess i specifically need to know which harness at the multi switch i need to be digging around. my wire colors don't match yours. the multi switch has 3 harnesses... 2 are plug style, and one (the closest one in the pic a few posts up) is like a direct splice (no plugs). I am seeing voltage on the orange wire at the multi switch, but the white wire next to it shows no voltage. is this the correct white wire? there is another one of smaller gauge on one of the plug style harnesses.

If this is the correct white wire (at the multi switch), can i splice a new one from the switch to the pedal? or do i need to trace it back to the big mass connector near the column?

thanks again for the help.

old_master · 02-11-2011, 07:54 PM

In your first post you said 2000, so all of the info that i have posted may not be correct. I'll check the 2001 schematic and post back.

viggy58 · 02-11-2011, 07:56 PM

yea sorry, found out today it's an '01 :-)

we're taking a couple days off from working on it, so take your time.
i think he may go ahead and buy a multi switch anyways. the turn signal shaft was broken off at somepoint and is currently glued together. he wants to fix that anyways.

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