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#1 |
Senior Member
![]() Join Date: Jul 2009
Location: Exeter, NH
Posts: 791
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High Beam issue
I went on vacation for 2 weeks and left my 1969 GMC C-1500 truck sitting in my garage. I went to open the hood and it was hard and wouldn't stay up, one of the lift cylinders on my billet hinges stopped working. Ok I called and have two new ones coming. Then yesterday I was checking my lights and turned on the headlights low bean and lights all worked hit the dimmer switch for high beam and low beam went out and the high beam didn't come on ! I bought a new dimmer switch no change. I have been chasing wires from the bulkhead to everywhere they are supposed to be. Nothing. The light switch was new 5 years ago and everything worked 2 weeks ago !!! Where do I go next? I think my truck may be mad at me.
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#2 |
Registered User
Join Date: Dec 2017
Location: Elkhart, Texas
Posts: 1,715
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Re: High Beam issue
First step is to round up three important tools (1)test light or volt meter, (2) wiring diagram, (3) A well-fitting "do not assume" hat.. Guessing and throwing parts, and hoping something sticks is not a proper repair method..
Voltage comes from the headlight switch to the dimmer switch through the light blue wire.. Since you have low beams, that circuit is working.. At he dimmer switch, you should have voltage alternating as you "flip" the dimmer switch, on the light green and tan wires. If you don't, the switch is bad.. If you have voltage on both wires, check for continuity on both these wires at the firewall connector, Again, alternating on each of these wires on both sides of this connector. If voltage is present on both wires on both sides of the connector, continue checking the wires inside the harness for breaks.. Check for voltage on these wires at the plug at the headlight bulbs... |
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#3 |
State of Confusion!
![]() ![]() Join Date: Jul 2002
Location: Gulfport, MS USA
Posts: 46,901
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Re: High Beam issue
Last 4-eyed truck I had had same issue, turns out both hi-beam bulbs were dead.
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Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God! |
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#4 |
Senior Member
![]() Join Date: Jul 2009
Location: Exeter, NH
Posts: 791
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Re: High Beam issue
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#5 |
Senior Member
![]() Join Date: Jul 2009
Location: Exeter, NH
Posts: 791
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Re: High Beam issue
Did all that I am getting a new relay later this afternoon.
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#6 |
Registered User
Join Date: Jul 2008
Location: Eastern Oregon
Posts: 2,339
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Re: High Beam issue
Wiggle the plug at the bulbs.
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71 C-20 07 Magnum RT AWD |
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#7 |
Senior Member
![]() Join Date: Jul 2009
Location: Exeter, NH
Posts: 791
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Re: High Beam issue
did that it was all new American wire when I built it. It was working fine when I parked it two weeks ago.
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#8 |
Registered User
Join Date: Oct 2005
Location: Overland Park, Ks.
Posts: 5,217
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Re: High Beam issue
Check the plug at the dimmer switch. It is well known to get corroded. It is in a poor environment
George. |
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#9 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,646
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Re: High Beam issue
I must have missed something, didn't think these trucks had headlamp relays. If relays were added (great idea, btw) then yeah, that could be the culprit.
I would troubleshoot with a VOM or at least a test light before throwing a new relay at it, though.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#10 |
Registered User
Join Date: Jun 2013
Location: Somewhere
Posts: 3,078
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Re: High Beam issue
Cycle the dimmer switch 20 times.
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#11 |
Senior Member
![]() Join Date: Feb 2002
Location: Tucson, AZ USA
Posts: 7,281
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Re: High Beam issue
Are Rodents a possibility?
Here in the South West, Packrats will invade an engine bay in no time. They chew thru wires. A couple of months ago, one chewed thru #5 spark plug wire on the 350 in my '71 GMC Jimmy. I had started the Jimmy to move it out from under a canopy so I could work on my '03 Tahoe in the shade. The Jimmy started OK, but sounded rough. While working on the Tahoe, I dropped something small and searched under the engine. I didn't find what I wanted, but I did find a 1'' piece of blue 8mm plug wire. So I looked under the GMC's hood. Sure enough, the little SOB had attacked my plug wires. I put on another plug wire from a different set and it fired OK. But I was mad a nice Blue 8mm Taylor wire set was compromised. One local trick is to leave the hood up. Packrats won't nest where a cat can get at them.
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Every 25 years I like to rebuild that 292, whether it needs it or not. |
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#12 |
Senior Member
![]() Join Date: Jul 2009
Location: Exeter, NH
Posts: 791
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Re: High Beam issue
Thanks for all the help, I found the problem.
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#13 |
Registered User
Join Date: Dec 2017
Location: Elkhart, Texas
Posts: 1,715
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Re: High Beam issue
Looks like moisture got to it.. I hear it's a common problem with the relays in those headlight kits..
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