brake light problem

If the trailer hitch wiring isn't factory, find the connection where the trailer hitch harness is tapped in for brake lights, check for power there up stream of connection. Maybe corroded connection or scotch lock connector cut thru brake light wire(or bad T plug if used). R

If still nothing...check owners maual, again, for fuses under hood ( I know newer trucks have), check brake light switch is getting power and working, if it is probably multifunction signal switch in steering column bad :( . R

There is a block of fuses under the hood, close to the master cylinder, and inside, there is a socket for the brake light fuse/relay - as well as a sticker inside the cover that says where it "should" be. Now if I look into the fuse block, there is only metal connections on one side of the pins where the fuse/relay would fit into it - so I don't think there was ever one in there from the factory. There was probably an option on this truck or a larger truck that wasn't installed on mine.

The trailer wiring harness is the T-type connector that plugs into the factory wiring harness at the rear of the vehicle. I will unplug it and check for power there, but I think the problem is likely something under the dash.

The brake light switch is really in a tight spot - not looking forward to trying to get that off. Also, is there a way to determine if the problem is the brake pedal switch or the signal switch in the steering column?

On the brake switch, usually orange is hot, and white gets power when the brake pedal is pressed. Maybe you could make a probe wire to get in the back of the plug to test the wires with your meter. You would think/hope if the trailer had a problem with wiring, it would just pop a fuse in your truck. But tempoarily remove the T harness put back to factory and hope for the best. But it seems failure in the steering column on the signal/flasher switch is very common, GM just had a big recall on this in newer vehicles.....R

OK, I took the column apart, and unmounted the multifunction switch. You can actually unclip the plastic overtop of the wire terminals going into the switch and use a tester or multimeter to test. I see the flashing power on a pair of terminals when the turn signal lever is clicked, so I assume those wires are also the wires that go hot when the brake switch is pressed. Also, on the white wire, I can see power there when I depress the brake pedal, but nowhere do I see outgoing power to the tail lights. I am pretty sure this switch is the cause of my problems.

GM dealer quoted me $380 for the multifunction switch!!! At monsterautoparts.com it's $260, and at gmpartscheap.com it's $248. Quite a spread so far... so I checked locally - napa wants $236, Advance Auto Parts wants $175, and at Pep Boys it's $150. This does look like a more expensive part - it's got the turn signal arm w/cruise and wiper connections attached to it, as well as the hazard light switch is built into it.... but I think that $380 is way out of line.

I asked each store plenty of questions, and some seem like they know what I'm talking about, some of them seem like they have never seen a car before. Some of them ask me if I have cruise, and tilt steering (the dealer did, and told me there was a difference) and some of them don't bother to ask and when I prompt them they tell me there's just the one switch available.

Looks like I'll have to take mine around with me to these places and compare so that I get the right part.

SuperDave

Did u try a Salvage Yard ??

SuperDave wrote:

No, I didn't try a salvage yard. Depending on the item, I sometimes buy used, but in this case I'd rather just buy a new one. I ended up buying it from Advance Auto and that did the trick.

The switch was the problem, so replacing it did the trick. Now when I depress the brake pedal, I can see power on the white wire coming into the switch, and also on both wires going out of the switch to the tail lights as well. (One is purple, and I "think" the other one is green)

SuperDave

Dave, I'm having the same issue on my 93 GMC. How much of a pain is it to replace? I take it you pull the steering wheel and disassemble where the switch goes? Do the wires run all the way down the column? Any words of advise before I tackle this? Not looking forward to it, but I can't drive the truck with no brake lights...

Thanks!

SuperDave wrote:

What let go on the old one..anything melted or contacts just worn out?...R

I don't really know what happened to the old one. I'm assuming broken or burnt contacts inside, because externally, it looks fine.

I know the interior on your 1993 is a little different, but I can describe how much work it is on a 96. I didn't have to pull the steering wheel, just disconnect the airbag wiring and a good part of the dash. The cover of my column splits in half, top and bottom. The bottom comes off with 2 screws, and then there are 2 screws inside the column holding the top part on. The top part wouldn't come off very far because it doesn't slip over the collar of the ignition switch.. I'm sure there is a way to get the outer part of the ignition switch to come off, but I don't know how. Then the upper front part of the dash has to come off, as well as the bottom part of the dash - these are fairly simple to get off if you're careful - a few screws and the rest is friction fit.

The multifunction switch has 2 screws holding it down, which are very tight to get at if you don't take the steering wheel off - one faces up and the other faces towards the driver, with only about an inch or so of clearance between it and the steering wheel. I actually used a hex screwdriver bit that just fit in between and then used a tiny wrench to turn it. I really didn't want to mess with the airbag stuff inside the steering wheel. Then the wiring runs about a foot or so down the column and into a large connector under the dash. This connector had a bold in the middle holding it all together. Once you get this bolt undone, the connector comes away and can be split into 3 parts. You can then remove the switch and wiring completely.

I found that the 3rd high mount brake light actually gets power directly from the brake switch itself - seems like it's the only thing that doesn't run through the multifunction switch. I was really puzzled when that brake light worked, and the regular brake lights did not. The 4 way flasher hazard lights no longer working also kinda tipped me off that it wasn't a wiring problem.

Hope that helps.

SuperDave