2002 Chev/Silverado Headlight question

[TOOLMAN]

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

[Jim Becker]

Light wiring on late model vehicles has gotten complicated. For example, some DRL's use high beams in series so each bulb runs at 1/2 voltage. Unless somebody speaks up with knowledge that is specific to your model AND year, you need to get the right wiring diagram and trace things out.

[TOOLMAN]

Thanks Jim
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 oringin.
I was wondering if I could just jump in a new ground off the frame of the truck?
I did a test wiring for a temp ground wire and the headlights worked fine
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

[John *.?-!.* cub owner]

Does your truck by chance also use the low beams as running lights? If so the ground is probably going to a relay that switches a resistor in and out of the circuit. Also, some vehicles had a resistor in the ground circuit.

[TOOLMAN]

no it has its own set of Day lights
I fix it by running a new ground to the low beam ground wire and they work fine again
Thanks

[Jack fowler]

Maybe I can help,

Be careful what you ground, short-out and probe with a conventional test light, Voltmeter, ect. on the headlight circuit because; the daytime running lamps module is intergraded in the circuit.

If you check electronics always use a digital volt meter with 10 maga ohms of resistance

Most of the time with your issue; no low beams, it has been the headlight dimmer switch….. but never assume that is your problem until you diagnose the root cause. Good luck, if I can help you in any way, just drop me a line.

Follow this link:

http://docs.google.com/Doc?id=dcpqrttm_199c4gvr9

[TOOLMAN]

Jack and all
Thanks that is what I was looking for
I think it is going to be the dimmer switch and have one on order
It has been working fine with the jumper ground I installed so far
and nothing has shorted out.
I even get both headlights to stay on when on the high beams
weird?
I checked everything I can think of and have to be leaning towards the switch itself because everything else works fine except for the low beams.
Maybe all it needed was a new ground but I dont know why the low beams stay on when I hit the highbeams they use to turn off when highs went on?
So I will get new switch and disconnect the new ground wire and see what happens
Question Jack
Did you ever hear of the computer having to be reset so that lowbeams would work again by the dealer ?
Thats is what someone else said at a chevy group?
I got more info from the members here then on a Chevy Group
imagine that Great group of guys we have here
Thanks all

[Jack fowler]

Maybe I can help a little more…

To show you how the base headlight circuit functions, I highlighted the circuit description to the wiring diagram of your truck. I have a program in my P.C. to do such things but, my high school boys need the P.C.for their homework so…I did it by hand. Sorry for the color schematic but its all I have. Follow from left to right on the wiring diagram when you read the highlighted operation description.

Your headlight system does not use the Body Control Module (BCM) when headlight switch is turn to headlamps position. When switched to “Auto” it does. Let’s repair the low beam issue and than go to the DRL function if it’s not working after the fix.

As far as resetting the computer; the only module used on the circuit is the BCM and like I said it is not used on manual operation. You do have “logic locks” on modules and yes you have to reset them sometimes. If a reset is needed I know of a way to do it without the use of a scan tool and you can do yourself.

I don’t know what Chevy group you’re talking to, but the only GM forum I know of is in GM.Com. The people that participate in that forum, as far as I’m concerned are the best Auto/ Truck technicians in the world.

Remember read the circuit diagram highlighted color to circuit description highlighted color left to right.

Any questions let me know…..I’ll have more PC time on the weekend.


Click on the link for the info and a service bulletin update concerning DRL lamp bulbs.
Note: The last sentence is intentionally marked out with a black marker.

Jack


http://docs.google.com/Doc?id=dcpqrttm_205fgqt2r

[TOOLMAN]

OK
The Lights are fixed
Thanks to all and Jack I really appreciate you going through all the trouble pulling up the job sheets to trouble shoot them
as well as the fuel pump THANKS
The Headlights were the column mounted dimmer Hi-Lo turn signal switch
The multi-switch was the problem.
Once after a few hours of ripping apart the dash and steering wheel I was able to unplug and plug in the new switch

TA-DA
it works almost as good as new (remember I put it back together too LOL)
Thanks again now I can see while driving at night
Tony
Fuel pump on its way as we speak hope to do the bed removal and install before the weekend if the weather holds

[johnbron]

Glad you got it fixed T-man I have had an 02 D-max for a couple years now but fortunatly I have had no problems "YET".