Hello. I'm chasing something that seems crazy to me. I had brake lamp go out and figured I'd address the regular bulbs and do an LED conversion on my H2 rear tail lights. Not my first rodeo with this or other vehicles.
Everything works fine. Parking, Brake, signal, etc. Signals needed resistors for hyper flash.. no problem.
However now I have no white reverse lights. LED, regular bulbs, etc. Fuse is good, and with the truck in reverse there is 14ish volts in the socket. However no light of any kind will work in the socket.
Using a 12v power supply the bulbs and or LEDs are fine. I just can't even imagine why I can't get a light to work with voltage in either the left or right socket. I've tried to bend to tighten the contacts, nothing.
Is there some way I could be reading ghost voltage or bleed on a meter without enough power amperage to light a bulb? I know I'm reaching, but just out of ideas.
Best and thanks,
-Dave

 

Try a different bulb. Cheap china led bulbs don't always match the sockets.

 

Dave, also when your done make sure your cruise control still works, on my 05 I did the same thing your doing and I guess the lack of resistance on what would be the brake filament circuit caused the cruise to be non-functional, put back the old bulbs and problem was solved. I never got back to experimenting to find out what the deal was and just stuck with the old fashion bulbs.

 

H2-SUT = most likely answer
Hummerz = possible, even likely. There is a way to test that theory. Incandescent (your old backup lights) likely draw more amps than LED. Do those light up? Guessing YES. But try it with the LEDs in the other sockets(s). Do left and right separately. If the old ones do not light up, then you have bigger issues.

Try LED on one side, old bulb on other side. What happened?

Cheap LEDs are usually very expensive in the end.

 

A little but of an update....
Battery is reading 12.4 on the studs. Right backup socket is showing 15V. So awesome I'm making power!
Left socket is reading about 9.9V. So I'm guessing these voltage readings are not very strong and really not enough amperage to light anything.
I'm wondering about the under bumper circuit board. Maybe I need to look at the pin outs to see if it's maybe the board. I did try disconnecting the left and right harnesses to see if it improved either side. No luck.
Tomorrow is another day. Thankful I work from home!
Thanks for the advice!

 

There is a circuit board under the rear bumper? Where?
I guess I do not know the hummer as well as I thought. Unless you are referring to some junction box or something, and not an actual circuit logic board?
Or is this something you added for the LED lights to work? LEDs these days are plug-and-play, so that should not be it.

Left socket is reading low? Did you measure with nothing in the right socket? i.e. no LED or other bulb in that socket, to make sure it is not causing resistance in the circuit (in case L and R are somehow connected in series rather than parallel)

 

They Call it a circuit board. It's really a distribution board. Seems to breakout 8 circuits.f

 

Thanks for the pic. You sure the H2 has that? Or is it some kind of generic J-block? Look at the wire color markers on it.
I have not looked, but why so many pins (28) for a 2 lamp circuit, which requires a total of 6 wires/connections/pins?
As suspected, photo is of a junction block (aka distribution block, aka Black Box, aka terminal box).

You sure the H2 has that?
Because the reverse light circuit is about as simple as it gets for wiring, and it does not need any sort of black box.
A simple connector should suffice. Then all that you would need to do is pull the connector apart, measure the resistance on the left circuit to bulb off the cold connector half, and ditto for the right circuit, and compare. That would tell you if the wiring is good on the "bad side". Then check power output from the hot side of the connector, again left and right sides, to see if you get ~12V on both sides. If you do, all is good, and problem has to be in bulb, or connection of bulb to socket. Pretty simple stuff.

Let me know what you find.

If you are sure the H2 has that black box, rather than just a simple multi-wire wiring harness connector, then:
It may just have wires connected to pins, or it may have resistors, etc. inside. Maybe even an circuit board? Maybe @oceanbrave can chime in, as he is good with electronics.
Maybe you could jump the junction block, to see if you are losing voltage thru it, and if it is the culprit. Or just put a voltage probe on the hots for the reverse lights, if you can identify them
But I doubt that is what the problem is. But I have been fooled before, and Hummers have some very weird acting electronics on them.

 

It's really not a black box. It's 8 wires in and 7 wires out to each tail light.
It's just more of a solid state way of dividing out the power leads. I've seen some mention of internal melting.
I know it's there under the truck, I need to test the pinouts on the input wire to see.
After this we are headed under the dash and that's going to start getting more complicated. I REALLY hope not to need to find a new BCM.

Option 2 is I could take the center pin from the trailer wiring and splice that to the reverse lights, but I hate the idea of mixing circuits and "Dave" fixes.

 

OK, my misunderstanding. I looked at your wiring diagram, and it is deceiving.
I did not realize that the same black box is a junction for MOST/ALL the rear end lighting, not just reverse lights, as that is NOT how it is shown on the diagram.

My other suggestions stand.

Let us know how it goes.