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Hummer H3For the Hummer driver who wants the rugged look and off road capabilities of the Hummer, but in a smaller size and with a more fuel economy friendly engine.
By "no brake/turn lamps in the rear" do you mean both left and right? If so, check fuse 20 and make sure its not blown.
Does the license plate lamp work? There is a known issues where the harness to the license plate lamp chafes and can short to ground where it routes through the rear bumper, which creates intermittent problems with the other lights. The license plate lamp is also on the same fuse as the right rear parking lamp (Fuse 49), but since that lamp is working the fuse shouldn't be the problem.
Did your truck come from the factory with the trailer hitch and wiring, or was that added afterwards? If this was added afterwards and they spliced into the tail lamp wiring instead of using the factory provided trailer wiring that is blunt cut in all H3 harnesses, there is potential to create unexpected problems in the lighting circuits and/or damage the BCM.
The rear right turn and brake lamp issue could be a problem in the aftermarket LED light housing you have installed, assuming whoever installed it followed the factory wiring diagram and didn't jumper off of other things. Power to the two filaments in the normal tail lamp bulb comes from two sources. The brake/turn lamp filament is powered directly from the BCM, where the parking light filament is controlled by a relay and has its own fuse. The right rear and left rear parking lamp have independent fuses after the relay. Within the BCM the schematic shows that left and right tail lamps are in the same logic group and share the same fuse with the LED turn indicator lamps in the instrument cluster. When you are experiencing your intermittent problem with the turn indicator, does the turn lamp in the cluster show the turn lamp is working, or is it dark? Do the brake lamp and turn lamp intermittent operation occur at the same time, or are they independent of each other?
The heater fan, marker light and accessory jack issues are almost certainly not related to the BCM and lighting, and are probably separate issues unrelated to each other. That means they should be investigated one by one. Just to confirm that, did you notice if these issues come and go independently, or when one isn't working, none of them are?
The aux connector not working could be a fuse - have you checked those? One of front aux ports is on the same fuse as the aux port in the back (Fuse 45) and the other is on its own fuse (Fuse 51).
The front left marker light is on the same power circuit as all the other parking/running lamps, and since all the other lamps work it is most likely a blown bulb. It could also be a broken wire in the wires connecting to the marker lamp socket.
The blower motor high speed operation is controlled by a relay attached to the bottom of the blower. If the relay is failed or missing then when you put the control to "high" the fan will stop working - is that what you are experiencing?
I will say that if the folks that rewired your harnesses didn't use the factory schematic to replicate the wiring and just jumpered stuff wherever then all bets are off on being able help you troubleshoot this. In that case you will need help from someone who knows how to read a schematic and use a voltmeter to troubleshoot electrical wiring problems.
yeah for sure. This is super frustrating.
thanks again for everyones help.
going to try to do some tracing tomorrow with the multi meter to see what we can find.
that ground does not look too hot. maybe take it apart and hit it with a wire brush or some sand paper. if that stud is held on with the other bolts i would probably want to expose some fresh metal on the mating surfaces as well. might have some rust scaling behind it. also maybe check inside of that short piece of wire loom at the hitch maybe its hiding something.
Took the ground apart cleaned everything and no change. The wire cover wasn’t hiding anything. The tag light works Can’t recall who asked that.
replaced both brake light harness with new ones. Checked all the wiring to my ability several times.
tried finding a place to sell me a clone but all of them say out of stock or unavailable.
gonna reach out to the shop again tomorrow but not holding my breath for any better results.
again thank you to everyone trying to help.
im open to offers at this point. Works great except this electronic issue.
i can provide the very long list of upgrades etc to anyone interested.
Someone has cut a number of wires from the BCM top connector (two green, one blue) and spliced in a new wire (red) off the bottom connector. Maybe you can match those wires up to the images Hummerz posted and figure out what they are for.
The tail light wiring similarly had added wires (the red ones) and splices (on the green wire) not present in the factory wiring. All bets are off until you figure out how its been rewired and why they did it that way. At this point the factory wiring probably isn't much help.
Looks to me like that ground stud is the one of the left side of the rear cross member. If so, it has some extra things added to it from stock. In stock configuration that stud is used only for the fuel pump sender, the license plate lamp and the trailer connector. One by one give those wires a tug and see if they pull free - that area is a hot spot for corrosion. On my truck those wires had corroded internally and had to be repaired.
The factory wiring diagram isn't going to be much help to you, other than to maybe figure out what's been modified from stock. I don't think you'll make much progress unless you can figure out how they rewired it, then figure out if that rewiring is appropriate or messed something up. It might have worked for a year or two, but if they put too big a load on a BCM output, or tied together some circuits that shouldn't be tied together, then stuff is eventually going to fail. There's probably a good reason the GM engineers didn't have more than one bulb on each BCM output.
didnt have any broken wires everything looks like it should.
i did find the one red wire that is hot bit didnt see anywhere it should be connected.
Wtf? No broken wires? Someone hacked the harness in all your pictures which needs attention to restore!
Start by removing that blue quick wire splice connector then check for battery voltage with brake switch on to the green wire.
I’m not sure what the red wire gos to but it looks over heated.
The green wire in the back seems to be a ground. no idea wtf it gos too.
I reached out to another electrical shop who said then can do a trace on the circuits the first of the month.
I did learn that the BCM circuitry for the hazard lights in the front and the back, etc. are all on completely separate circuits some go through the fuse box while others go through the BCM
i am learning a lot about automotive electronics.
thanks again to everyone trying to help.
what a frustrating adventure this is.
