Fuel Gauge troubleshooting

[dsmayer]

The fuel gauge on my 78 Spider won't work. I replaced the sender and the gauge. It always stays on empty and the red low fuel indicator light comes on only when the tank is full. Does someone know the steps to troubleshoot this?

thanks,
daryl

[mbouse]

there are two wires from the sender to the dashboard.

try reversing those two wires.

[msova]

yeah...sounds like a classic case of the wires at the sender being mixed up.

Also...doesn't a ground wire from the sender to body help things?

[mbouse]

the tank is steel, and bolts directly to the body. the sender is steel and bolts directly to the tank. if the mounting surface is clean, there should be no need for an extra wire. the extra wire is not necessary in this situation, a signal is being sent from the sender to the gauge.

if there were zero signal at the gauge, your suggestion might be a possible solution.

[4babycar]

I don't mean to be rude and hijack another person's post but I am having a similar problem. I have replaced the sender and I have tried switching the wires. It ends up that the gauge either reads that I have a constantly full tank (Oh, if were really that easy) or a constantly empty one. Any advise there? Also the sending units that I have are isolated from the steel tank by a thick rubber gasket.

[mbouse]

the top of the steel sender bracket touches the steel screws that thread into the steel tank. the rubber gasket is for leak proofing.

does you red light come on with either of these settings?

also, the gauge needs a good, clean, tight ground as well.

[So Cal Mark]

with the key on, remove the two wires to the sender and ground them one at a time. When grounded, the wire for the gauge will cause the gauge to read full, the wire for the light will cause the light to come on. If the gauge doesn't read full with the wire grounded, you have a gauge or voltage problem

[4babycar]

Once it stops raining, I will go out and see what I can find out.

Oh Mike, Duh...... I knew that...... I was just having a brain fart! Yeah, that is my excuse.

[dsmayer]

Success! I switched the two wires and the gauge works fine now. My son suggested this a couple of weeks ago, but I dismissed it because I reattached the wires on the new sender exactly as they were on the old one. Sounds like I've got a dose of "I told you so" coming.

thanks guys!!!
daryl

[kilrwail]

Once you've taught your children the best you can, always listen to them! They are never wrong! Just ask them

[mbouse]

the more we think we know about our cars, the more complex solutions we seek for simple problems... at least, that is my excuse (and i am sticking to it).

[maytag]

with the key on, remove the two wires to the sender and ground them one at a time. When grounded, the wire for the gauge will cause the gauge to read full, the wire for the light will cause the light to come on. If the gauge doesn't read full with the wire grounded, you have a gauge or voltage problem

This is where I'm at with troubleshooting my gauge right now. I've grounded them one at a time, as you've described, and the low-level light comes on, but the gauge does not move with the other wire grounded.

So here"s my question: where is it (the gauge) supposed to be getting voltage? My wiring diagram (in the Haynes book) BLOWS. My car is a '76. I'll pull the dash if I have to... but it'd be nice to do a little probing with a test-light first.
????

any help is appreciated.

[idocdan]

The wealth of information here is invaluable. Haven't had my spider long, and have been clearing issues up for the last few months. The latest was the fuel gauge--it always showed empty until it was near empty, then the needle would bounce around. After reading various posts, I switched the wires at the tank. Voila! You all saved my $50 for a sending unit. I love you guys!!!

[124JOE]

fuse i the second one from the left
haynes manual dose suck but thats what i have.joe

it says the wire is white

[124Germ]

I hate to resurrect an old post, but I am having a similar issue. My issue is that my gage constantly reads full. When I blew that fuse second from the left it went to empty. I recently bought the car a couple weeks ago and the PO said it was the sending unit. Prior to ordering a new unit I just want to make sure that the sending unit is the faulty product, rather than throwing money at a problem.

Thanks for all your help,
Jeremy