Hello again So heres the deal (NO Ground to low beams)
I went out with my multimeter in hand today and found that the
headlights have no ground on the lowbeams
now my most logical thought was to just splice in a new ground, so I
figured the highbeam ground was very close so why not use that
(Right?) Wrong I was then suprised to learn that when I spliced into
the high beam ground wire and tried the lowbeams all the headlights
now came on high and low beams .
So I figured that the grounds must run through a relay of some sort at
this point so I disconnected the splice I made and it is back to a no
headlight on low beams.
But here is my question can I just run a new ground wire spliced into
the lowbeam ground wire and ground it to the body of truck (because
lowbeams will work when grounded to the body I tested it and yes they
worked as they should (but I thought the wire I was using got a lil
hot so I did not leave it connected to long).
Or are these headlights designed by GM to be grounded only through a
relay to avoid burnout?
Or can I go ahaed and just use the spliced in ground and use the low
beams safely the way the new ground is?
Thanks again for all who respond
I have tracked the problem to the low beam ground
But can not for the life of me trace the ground back to it point of
I was wondering if I could just jump in a new ground off the frame of
I did a test wiring for a temp ground wire and the headlights worked
I am just nervous about jumping in a direct ground just in case like
you said there is 1/2 voltage involved.
But when I placed a volt meter to the positive lead to the bulb and
then ground the other lead to the frame and I did get 11.79 volts (12v
lets say correct)
I can not see why I can not just replce the ground wire at this point
I would cut the old wire and install a new ground and see what happens
any ideas Thanks again
You would have that scenario without a ground.
I don't know if that is switched by the ground, but if you have that voltage
at both bulbs. It would be indicative of a bad ground.
I sincerely doubt that you'll hurt anything by momentarily touching a
ground, to see if the lights work.
If they do, leave the ground on, and see if the lights go off when you shut
most likely combination switch chould have no problem makeing a ground at
the lights i have done it a couple of times and had no problems
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I've pulled up the schematics in GM-SI, and will describe the circuit.
The headlights are hot all the time, fed through 2 fuses in the
underhood fuse block, one for high beams, and one for low beams. The
common side of the dimmer switch is grounded. When switched to low beam,
the ground is routed to the underhood fuse block and out through what
appears to be a jumper, then to the low beam filament. Ditto for high
beams. You know the ground is good, becausse you have high beams. That
1. The dimmer switch.
2. The wire from that to the underhood junction block.
3. The jumper in the underhood junction block.
4. The wires from the underhood junction block to the low beam filaments
of the 2 bulbs.
You shouldn't have a ground at either high or low. That truck uses a
ground switched system. The dimmer and light switches both complete the
circuit by turning on a relay that grounds the correct lights. since the
lights come on when you ground them the hot side is OK. Check the low
beam relay and it's wiring. Also look at the dimmer switch itself.
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