Topic: Need a wiring diagram for a fuel gauge.

[BARRACUDA1968]

I've installed aftermarket gauges in my 78 T/A.  I had to make my own dash harness to complete the job.  Everything works accept the gas gauge.  According to the Circuit Connector Pin Location sheet I have it say's

"1977-1980 factory rally pack gauge cars used a fuel gauge employing a separate 2 position connector"

I have the new gas gauge wired to the two position connector that went to the factory gauge but my gas gauge is pegged full.  My new gauge from Speedhut has a built in OHM reader and it's reading 500 OHM's or basically it's maxed to what the gauge will read.  After talking to speedhut they say that means the gauge isn't reading any resistance.

My stock gas gauge worked fine before so I don't think it's the sender.

Here are some pictures of the stock wiring harness at the cluster before I started.



the other side



Then I made my own harness to install the gauges.



Here are the wires I didn't use in my new harness

The two tan wires are brake light

The pink with white is seatbelt warning

If you notice in the two top pictures there are 2 black wires in the original harness.  The pin location sheet I referenced only shows 1 black wire??

Now I have one black wire left over.  I wonder if this has anything to do with the gas gauge?



I have the dash all back together so before I take it back apart I'm hoping to find a solution.  Someone on another board mentioned the gas gauge is a 3 wire affair?

Any ideas?

[BARRACUDA1968]

Here is the chart I used

[BlackTransAm]

The fuel gauge has a separate connector, not part on the one in the first pic,  separate 2 pin conector.
 Thats the main gauge harness, look for the other that hooked to the fuel, volt meter off to the right ,
should be easy to find and hook up

[BlackTransAm]

Heres a pic of it

[BlackTransAm]

Here is aclose up

[BlackTransAm]

I  think this is what your looking for, just cut wires and attach to your new gauge
 If Ohm range of new gauge is the same as stock should read as accurate as old gauge
 90 Ohms full , 45 Ohms 1/2  tank 0 empty

[BARRACUDA1968]

Thanks for the help but I already have the fuel gauge hooked in to that connector and I'm not getting a reading at the gauge.

I was wondering if that 2 pin connector that went to the original fuel gauge is wired in to something else (the gauge cluster harness) to complete the circuit and by not hooking up the other black wire in the picture I broke that circuit??

I can't seem to find a wiring diagram for the fuel gauge itself online.  Maybe I'll have to just run a separate harness for the gauge to the sending unit?  The kit came with enough wire to do it but I just tapped in to the car instead.

[BlackTransAm]

The black wire is a Ground and if you dont have the ground hooked up you shouldn't have lights or a lot of things?
 It should ground the cluster and  light switch but I dont think the fuel guage.
 Hook the old gauge up and see if it still works ,if not, yes you broke the circuit some where, maybe that ground.
 Ground that wire and find out. You cant hurt anything by grounding a ground.

[BlackTransAm]

PM your email, I have the schematics , but to big to post here

[BARRACUDA1968]

PM sent

Thanks

[BlackTransAm]

I sent him all I had, 78 diagrams are hard to find, I have 77, 79,80 I found one on another forum I think was 78
anyone have them?

[BARRACUDA1968]

I'm looking at the 79 diagram and the cluster harness doesn't match my harness??

Ok we know that the tan wire comes from the sending unit in the trunk.  Then does it go straight to the gauge? or somehwere else first?  The diagram I'm reading shows it going to the cluster but as you see in the photo's up top I never had a single tan wire at my harness to begin with? The double tan wires are for brake warning.

The pink wire goes to the ignition off the gauge right?  Where does it get power?  Fuse box or cluster?

Sorry to drag this out but I'm having a hard time following these diagrams.  I only have 79 and 80.  79 is supposed to be the same as 78 I guess? My 79 diagram doesn't show the wiring to the fuel gauge just the fuel sending unit.

[BlackTransAm]

The one link I sent you has the 77 diagram, power runs from fuse box to ignition red wire, then pinkwire to connector
here's a thread http://www.78ta.com/HTAF/index.php?topic=39838.0 what colors were running to the gauge?

[BARRACUDA1968]

They were both  pink if I remember right?

I think I might have it now? Looks like the tan wire goes straight to the gauge from the fuel sending unit.  It may turn pink at a body connection along the way. Then the pink wire to the fuel gauge gets it power from the gauge fuse at the fuse box.

[BlackTransAm]

I agree the pink wire is all guages power, then one, I dont know what color runs to the fuel guage then tan runs to sending unit from guage,
It should be same color at connector and guage. Use a meter to check tan at guage for ground, then you know its working, then check continuity of the other guage wire to connector to determine exactly which one it is.
 Then let me know which one.
 the diagrams aren't clear because they include cars with fuel guage in main dash cluster, non-rally