Author Topic: Fule gauge falls past empty when I turn on the head lights.  (Read 3250 times)

Offline Todd7080

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Fule gauge falls past empty when I turn on the head lights.
« on: March 29, 2011, 11:12:35 PM »
 Hi everyone Im new to this site as far as being a member but have used info from here for years. I just put a better looking set of gauges in my original housing and when the key is turned on the needle went to the correct spot. With the key off I turned the headlights on and the fuel needle fell to the left way past the E. if I turn the key on it goes to the correct spot again. i didn't have this problem before I started and that frustrates me. The printed circuit in only 4 years old also. Any help would be much appreciated.
 Thanks...
1970 C-10 SB
1980 C-10 LB for now
1987 R-10 LB

Offline 1979C20

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Re: Fule gauge falls past empty when I turn on the head lights.
« Reply #1 on: March 29, 2011, 11:50:07 PM »
Why would you turn your headlights on without the key on or the truck running? And, it sounds like maybe a ground problem. My gas gauge hardly moved at all and it would run out of gas on my when it was still over 1/4 tank. But I found the ground wire from the back side if the passenger.head into the fire wall was iff and I hooked it up and now it works how it should and E is actually empty. Check your gauge ground wire and make sure you have everything hooked up right.
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline beastie_3

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Re: Fule gauge falls past empty when I turn on the head lights.
« Reply #2 on: March 30, 2011, 01:31:08 PM »
if the fuel gauge is correct with truck ON and lights ON, then I wouldnt worry about it.

Offline bake74

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Re: Fule gauge falls past empty when I turn on the head lights.
« Reply #3 on: April 01, 2011, 09:40:09 PM »
     1979c20 is on the right track, has to be a wire issue.  If it was me I would go to the tech section here and get the wiring diagrams for your truck, then trace the fuel circuit and headlight circuit ( you might want to try to see if other switches do it also ), it really sounds like to me that somehow you grounded/crossed the two circuits,and with out the truck running you turn on the headlights and "drain" the power from the fuel gauge circuit.  Electrical issues can be a nightmare and a headache, but if you approach it with a plan and remember to take the simple steps first you should be able to trace the problem. 
     Good luck and keep up informed, welcome to the site also from California.
#1: The easiest and most obvious solution to any problem is 99% of the time correct.
#2: There is no such thing as impossible, it just takes longer.
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Offline Todd7080

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Re: Fule gauge falls past empty when I turn on the head lights.
« Reply #4 on: April 04, 2011, 10:43:10 PM »
Thanks everyone for the input. I will take the dash back apart and find the issue soon. I can't stand things not working like they are supposed to. What boggles my mind is the gauge I took out worked like a champ. I just replaced it because it didn't match the rest of them.
1970 C-10 SB
1980 C-10 LB for now
1987 R-10 LB

Offline beastie_3

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Re: Fule gauge falls past empty when I turn on the head lights.
« Reply #5 on: April 04, 2011, 11:16:13 PM »
If all you did was replace the gauge, then it could just be the new gauge...Put the old one back in and see what happens.