# Fuel Gauge & Gen Light Issue



## OrbitOrange (Jul 5, 2010)

Fuel guage has been reading past full. Even after installing a new sending unit months ago. Today I decide to tackle it. 

Using a test light I grounded the gauge on the left post (looking at back of cluster). Fuel guage falls to empty. Test performed with key in the "on" position. This indicated to me the gauge is not faulty.

2nd Test: Unplug harness to rear of car located under dash. Testing the "tan" fuel sending using wire using a OHM meter Im seeing 19 ohms. (0-90 full for reference). This indicated to me the sending unit is also not faulty.

3rd Test: Where the under dash plug for the rear harness is bypass wire from harness to the cluster. Using a scotchlock run jumper wire tan sending unit wire to the left post of the gauge. Seems to make the gauge either work or go to empty (unsure since Im not sure how much fuel is in the tank although I got a 19 ohm reading from the sending unit) This indicated the tan wire from the under dash connector to the cluster is faulty. But now the GEN light is lit up. Before it was very dim and only visible at night.

4th Test: Crank the car test voltage at battery and get 14.5 volts.

5th Test: Remove GEN bulb , crank car test voltage at battery again and get 14.5 volts. (NOTE: I do have a new engine harness and adapter for the internally regulated Alternator)



Here is my problem. Since I am running an internal reg. Alt. Do I need to have the GEN bulb installed to self excite the alternator? Or can I leave it out and be done with this problem? Or can someone tell my what caused the GEN light to come on after making a jumper for the Fuel gauge?

Im only assuming the fuel gauge now works because its not reading past full. Sad as it sounds. I dont have the money to pour a couple of gallons in the tank to see if the gauge operates properly.


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## BearGFR (Aug 25, 2008)

Are you sure that the printed circuit board on the back of your cluster is correct for the harness you're using? I had a weird GEN light problem on my 69 and that turned out to be the problem. The GEN light was seeing the signal that should have been going to the temperature gauge, so the warmer the engine got, the brighter the light got.

Bear


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## Eric Animal (Oct 28, 2007)

Assuming your problem is NOT as Bear's was,,,the Alternator with a single wire "self excites" at a set alternator RPM....600 up to 2000 depending on the unit.


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## OrbitOrange (Jul 5, 2010)

Eric Animal said:


> Assuming your problem is NOT as Bear's was,,,the Alternator with a single wire "self excites" at a set alternator RPM....600 up to 2000 depending on the unit.


Thanks Eric, so I could remove that buld if I wanted and it wouldnt interrupt any other circuits from what I can see in the diagrams correct?


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## OrbitOrange (Jul 5, 2010)

BearGFR said:


> Are you sure that the printed circuit board on the back of your cluster is correct for the harness you're using? I had a weird GEN light problem on my 69 and that turned out to be the problem. The GEN light was seeing the signal that should have been going to the temperature gauge, so the warmer the engine got, the brighter the light got.
> 
> Bear


Well Bear, to be honest ( hope you can follow me on this cause when I explain it to someone I usually have to explain twice or more! LOL) My car is a 70, but, it has a 69 dash in it. Before I restored it, it had a 69 dash harness. When I restored it I put the 70 harness in it. But not sure which circuit board I actually used because I did do some swapping of the gauges during the rebuild. Some were old looking some looked better so I used the best looking ones. But I cant remember which circuit board I used. 

Looks like I gotta pony up some money to put some fuel in and see if the gauge reacts to a new fuel level to honestly see if its working or if its now stuck on E instead of F. Geez this is driving me nuts! I guess if all else fails. Ill put in an aftermarket fuel gauge. I did that in a mustang once and hated it. The aftermarket ones don't have a slosh module in them so the needle really floats alot on inclines and acceleration/deceleration.


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## Eric Animal (Oct 28, 2007)

It SHOULDN"T interupt anything else.....If you go that route, put in a known burnt out bulb...that way the socket will have something in it.


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## 68GTO4004Spd (Jun 19, 2008)

This may sound stupid, but do you have the grounding strap from the engine block to the firewall? My guages were doing all kinds of crazy crap until I noticed the strap was missing after the guy put the engine back in.


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## Eric Animal (Oct 28, 2007)

:agree, it's possible...also...could be a bad alternator. We had a single wire alternator feeding back a little juice into the dash directional signal lights.....Strange, But True!


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## OrbitOrange (Jul 5, 2010)

Ya know. After I put the car together I cant remember if I put a ground from firewall to block. I know I put one from block to the frame. Im gonna check that. Cant have to many grounds!


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## Eric Animal (Oct 28, 2007)

I hope you find out that it IS just a ground issue. Eric


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