Electronics Need help wiring something up? Thinking of adding an electrical component to your car? Need help troubleshooting that wiring glitch?

Light switch turns on fuel pump?

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Old May 12, 2014 | 10:36 PM
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Car: '91 GTA
Engine: 421sbc
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Light switch turns on fuel pump?

I took my dash out this winter to install a roll cage.
I thought I put all the wires back in place, guess not.
Now when I turn on the lights the fuel pump primes! Without the key in the ignition.

Also when the lights are on, the dash lights are very dim and the turn signal and high beam indicator light are on!
Then when I turn the interior lights on the dash lights come on and the turn signal and high beam indicator light turns off.

Any help?
I have wiring schematics and tried to follow wires but I am very weak in the electronics dept.
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Old May 13, 2014 | 10:03 PM
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Re: Light switch turns on fuel pump?

Bump?
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Old May 14, 2014 | 07:47 AM
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Car: 1983 Z28
Engine: 385 Fastburn
Transmission: T-5
Axle/Gears: BorgWarner 9-bolt posi, 3.27 gears
Re: Light switch turns on fuel pump?

Oh wow, sorry but reading that made me laugh, just sounds like a sitcom moment or something.

It sounds like you just have some wires crossed, that should be easy enough to track down since you have the schematics. Just open it back up and do some tracing. There shouldn't be a lot of work to it, just gotta make sure xyz-wire is connected where it's supposed to be, they should all be color coded.
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Old May 14, 2014 | 12:41 PM
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Car: '91 GTA
Engine: 421sbc
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Axle/Gears: Ford 9" with 3.89
Re: Light switch turns on fuel pump?

That's what I thought too that I got lines crossed.
Problem is that they can't be crossed! The wires have unique plugs that only the correct wires will go into.

I checked the grounds and so far so good.

I guess I'll keep digging.
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Old May 14, 2014 | 12:53 PM
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Car: 1983 Z28
Engine: 385 Fastburn
Transmission: T-5
Axle/Gears: BorgWarner 9-bolt posi, 3.27 gears
Re: Light switch turns on fuel pump?

Originally Posted by LB9GTA
That's what I thought too that I got lines crossed.
Problem is that they can't be crossed! The wires have unique plugs that only the correct wires will go into.

I checked the grounds and so far so good.

I guess I'll keep digging.
Oh, so you didn't do any splicing or anything while it was apart?

that's really odd.
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Old May 14, 2014 | 12:54 PM
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From: Louisville, KY
Car: 1983 Z28
Engine: 385 Fastburn
Transmission: T-5
Axle/Gears: BorgWarner 9-bolt posi, 3.27 gears
Re: Light switch turns on fuel pump?

Might be worth a shot to unhook the battery for about 10 minutes and hook it back up, see if resetting the computer fixes it.
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Old May 14, 2014 | 01:45 PM
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Car: 1988 Trans Am
Engine: L03
Transmission: 700R4
Axle/Gears: 10 Bolt 2.73 Open
Re: Light switch turns on fuel pump?

I was hoping someone with some more first hand experience with these I/Ps would post. But my first mipression from reading your thread was that you have a harness pinched somewhere when installing the dash. Circuit wires are crushed together at that pinch point, letting power bleed from one circuit to another.
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Old May 14, 2014 | 10:22 PM
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Car: '91 GTA
Engine: 421sbc
Transmission: Powerglide
Axle/Gears: Ford 9" with 3.89
Re: Light switch turns on fuel pump?

I just installed the dash wires. I didn't splice any.
I have a battery disconnect and that doesn't work.
Besides, I don't think it's an ECM problem as the car still starts and runs.
I found a couple more grounds and tightened them but nothing still.

Does anyone know how many grounds are underneath the dash? And where they are located?
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Old May 20, 2014 | 11:15 AM
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From: CenTex
Car: 1988 Chevy Camaro RS
Engine: 1994 L05
Transmission: 700R4
Axle/Gears: STOCK
Re: Light switch turns on fuel pump?

4 grounding points not positive were they are.
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Old May 20, 2014 | 11:18 PM
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Car: '91 GTA
Engine: 421sbc
Transmission: Powerglide
Axle/Gears: Ford 9" with 3.89
Re: Light switch turns on fuel pump?

It's a bad ground somewhere!
I found it! Kinda!

On the passenger side behind the dash there is this connection
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What is it?

When I ripped the dash apart (again) I was moving wires and connections around and accidentially touched this connnector to the computer and voila! The bad ground went away! When I touch the outside of this connection with a test light, it has power!? When I back probe the ground from this connection it has power!
But when I touch this connection to the computer(to give it a ground) , the weird dash light problem goes away!
Name:  20140520_221953.jpg
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Size:  37.5 KB

SO! My question is this!?
Can I just ground this bad connection and my problem is solved? Or do I have to trace through the rats nest of wires to actually find the bad ground?
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Old May 20, 2014 | 11:21 PM
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Car: '91 GTA
Engine: 421sbc
Transmission: Powerglide
Axle/Gears: Ford 9" with 3.89
Re: Light switch turns on fuel pump?

Come to think of it!
When I was removing this connector, it was bolted to the metal frame of the dash before, therefore that was probably giving it the proper ground that it needed.
D'oh
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Old May 20, 2014 | 11:28 PM
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From: Andover, MN
Car: 1989 Trans Am GTA
Engine: 5.7L TPI
Transmission: 700R4
Axle/Gears: Stock 9bolt posi
Re: Light switch turns on fuel pump?

Don't worry man, we all make stupid mistakes. I tore my whole dash out once because my car wouldn't start.

Turns out, the starter wear material was so worn out, it was preventing the starter from turning. yeah.
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Old May 22, 2014 | 11:10 PM
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Car: '91 GTA
Engine: 421sbc
Transmission: Powerglide
Axle/Gears: Ford 9" with 3.89
Re: Light switch turns on fuel pump?

Can anyone identify the silver relay/connection?
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Old May 22, 2014 | 11:21 PM
  #14  
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Axle/Gears: Ford 9" with 3.89
Re: Light switch turns on fuel pump?

Another question.
In my schematics it says ground "j" and "h".
But it doesn't specify the location of said ground.
Any help?
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Old May 23, 2014 | 04:35 AM
  #15  
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From: Kitchener, ON
Car: 1988 GTA
Engine: LB9
Transmission: T5
Axle/Gears: 3.45
Re: Light switch turns on fuel pump?

That's the rear defog timer, and it gets it's ground from the black wire on the 2 pin connector in your pic. The defog switch also shares the same ground, so that's where I would start my search for a missing ground connection.
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Old May 24, 2014 | 10:28 PM
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Engine: 421sbc
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Axle/Gears: Ford 9" with 3.89
Re: Light switch turns on fuel pump?

You are correct.
I finally found it on the schematics.
I also found the missing "j" ground I was looking for! Its just above the drivers right foot.

Everything is back to normal

Thanks for all your help
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