Headlights on makes gauges go nuts!

79ElkyFl

I recently purchaced a 79 El and it is an electrical mess.My main problen is that when I turn on the headlights I lose all my gauges except for my speedo.Also when I use the turn signals the tach pulses with the turn signal.If anyone has any quick fix ideas or something to check before I try to reroute all the electronics i would appreciate it thanks.

elcamino74guy · Posted: Wed Jun 18, 2008 1:36 am Post subject:

Sounds like a short in instrument panel wiring.
First make sure the gauge cluster is fully seated into the dash.
There's usually a connector on the back of the cluster assembly
that fits into a socket in the dash.
Check for loose grounds and failing that you may have to
pull your column apart to check the column wiring harness for
shorts. I had a 79 Z28 that had a melted wire in the column that wouldn't let me shut the car off with a key. Turns out a wire had rubbed against the
inside of the column and shorted against an ignition wire.

Happy

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74 El Camino Classic - project car #1
96 Camaro - RIP, Traded 10-16-2007

2008 Mustang GT, It ain't a Chevy but at least it's American!

464elky · Posted: Wed Jun 18, 2008 6:21 am Post subject:

Like elcamino74guy said - CHECK THE GROUNDS - lay down in the drivers door and look straight above the hood release lever. There is a 10mm bolt that has the main dash grounds connected, or supposed to. Loosen it and clean the connections. Go to the headlight wiring and follow the black wires from the rear of the headlights to where they are grounded to the core support and clean them. Make sure you have a good ground from the body to the chassis and the battery to the engine block.
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79ElkyFl · Posted: Wed Jun 18, 2008 6:30 pm Post subject: ok now what

I chased the problem back to the dimmer switch if it is turned on I lose my gauges when it is off they are fine.Now after I got it all back together when I press the brake I lose the gauges this just happened and all I did was remove the dashcover and check the headlight switch wiring.Any suggestions

464elky · Posted: Wed Jun 18, 2008 6:52 pm Post subject:

The problem with your diagnosis is that the dimmer switch is always on - either high or low - if the headlight switch is on.

Now the question is was the problem when it was on high or when it was on low.
As far as the new problem it is all related which is why I went the ground route. Grounds are the one thing that is common to everything on the car and when electrical things do crazy things like what you have that is usually where the problem lies. Maybe not this time but keep us informed of the progress and or failures. We'll keep trying to help as long as you keep feeding us more info.
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Another 3 to 9 years should finish it.

79ElkyFl · Posted: Wed Jun 18, 2008 8:47 pm Post subject: dimmer switch

Hello again the situation with the dimmer switch is this.When I turn the headlights on and turn the switch clockwise untill it clicks the gauges are not affected.Once I turn the switch counter clockwise the voltage and fuel gauge go all the way left or and the tachometer peggs right the more I turn the switch up the worse it gets If I go more than a third of the way counter clokwise the gauges the gauges do not work at all.I did check the grounds at the headlights as well as near the hood release they seem ok I will double check them with a voltmeter to make sure in the morning.I am not sure why depressing the brake pedal would affect the gauges but it now does the same as when the dimmer switch is turned on if I press brake I lose voltage and fuel gauge and the tach sticks at about 1000 rpms untill I press gas pedal in witch case the rpms increase untill I let off gas and then right back to 1000 rpm.The previous owner/owners have a mess of wires under the dash and have an aftermarket alarm installed making it more difficult to find the problem.The alarm functions properly if I can figure it out I will definately post my solution but I am still open to any ideas thanks for the help so far.

elcamino74guy · Posted: Wed Jun 18, 2008 10:21 pm Post subject:

Check the grounds to your lighting circuit as well. The only thing electrical that the brake pedal turns on is the brake light switch. Also the brake warning light if your master cylinder goes out but that ones really not connected to the brake pedal, it's in the master cylinder itself.

This really does sound like a grounding issue though. Checkt the grounding straps from your engine to firewall and hood too. They're important as well since the negative battery cable (ground) is usually hooked up to the alternator bracket. That's the most direct ground the car has and if the ground straps aren't in good shape it can affect the grounding of the whole car.

Now that I've beat this topic into the "ground" Happy

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74 El Camino Classic - project car #1
96 Camaro - RIP, Traded 10-16-2007

2008 Mustang GT, It ain't a Chevy but at least it's American!

79ElkyFl · Posted: Wed Jun 18, 2008 11:54 pm Post subject: lights

Ok I will definately go over the ground wires I recently purchased this car so it is not like this just happened.It is likely that the previos owner wired something incorectly.I drove the car this evening and the brake being depressed is engaging my interior lights even with the dimmer off.If there is a short or a grounding issue it is likely in the wiring of the interior lamps.I will try to pull the fuse out and see if that helps if so I will have a hell of a time rewiring the lights a gauges.could a grounding issue somewhere else cause these problems in a different location?

CoyoteOn2 · Posted: Thu Jun 19, 2008 1:57 am Post subject:

Anything in your lighting circut can cause you this type of problem, even a badly grounded Tail Light. Sorry, but as stated before, start checking your grounds, and there are alot to check. Electrical feedback due to a poor ground will play havic on an electrical system.
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