Thanks for reading. Any advice is appreciated.
My guages aren't working. The oil pressure and temperature don't read anything. The gas guage reads full with just 7 gallons of gas in it. The DC guage looks good.
I replaced the fuel tank, sending unit, and voltage regulator behind the dash. Before doing all that, I cut the yellow fuel wire midway between the fuel tank and engine and grounded it to the frame to see if the gas guage worked because it was stuck on E. It jumped to F when I grounded it so I knew it had to be the sending unit. The tank was all rusted and full of rust sediment so I replaced that, too. Now it's reading full! Ugh! I compared the sending units and they were exactly the same. The tanks looked the same, too. Where should I go from here??

 

Gas gauge: If you cut the wire and ground it and can watch the dash gauge react, that very strongly implies the problem is with the sending unit in the tank. I have had problems with Spectra Premium sending units and don't trust them myself; in any event, i would remove the sending unit and wire it up outside the tank, then move the float lever arm thing and see how the dash gauge reacts.

The other two gauges work on the exact same principle; power from the ICVR into the gauge, the ground meets a variable resistance via the sending unit. Perform the same tests here; turn the ignition on, remove the wire from the sending unit, ground it to the engine, see if the gauge reacts.

Are the wires even hooked up to the engine's sending units?

 

I went with a dorman sending unit. Looked just like the original.

Today, I cut the green wire from the temperature unit that's close to the thermostat and grounded it. Nothing.

 

Eeeeeeeeeeeeeeeeeeeeee, I hope you didn't hurt anything! That looks like a multi-wire device (is it?) which is the temperature sensor used by the computer and NOT the sender used by the dash gauge!!!! Two totally separate devices, the computers were add-on installations at the time and the functions weren't integrated into one device.

The temp/oil pressure gauges use one-wire sending units; one is red/white-stripe and the other is white/red-stripe, I forget which is which.

That looks like a 6-banger engine; IIRC the oil pressure sending unit (aka sender) is on the passenger side way in the back by the firewall; with that, the other red/white wire is the water temperature sender.

I really hope you didn't damage the computer doing that.

 

Ah, yes, I mistook the temp sender as the oil sender. I see the temp sender. I've read that I need to buy a special size socket to take it out?

Yes, its a 6 banger.

I'm assuming its not the voltage regulator as the fuel gas is reading 'something'. Is this correct?

 

Yes, that's correct... when the ICVR (Instrument Cluster Voltage Regulator, ND Bill will yell at me if that's wrong) wigs out, all three of gas, oil & water gauges wig out together.

I've never used a special socket for those sending units but I guess they can optionally be used.

The important part is, red/white and white/red-colored wires, and the dash gauges use single-wire sending units; I REALLY hope the computer isn't damaged (although I suspect it'll be OK but that's only a suspicion).

 

Update. So I took off the wire to the temp sending unit and grounded it. Still no reaction on the dash. So then I took off the dash and removed the guage cluster. The oil pressure tab on the board was bent so it wasn't making contact to the cluster! I then put a jumper wire from the temp guage to the corresponding cluster wire and still no reaction (testing the contact of the cluster to the circuit board). Then I put a jumper wire from the guage to a ground. The guage then went to full! I then put everything back to where it belongs and the oil press. guage works now but still no temp guage. I'm assuming its the temp sender even though I grounded it from there and no reaction (must've been a bad ground point, I hope).

However, I must point out that the oil press gauge reads LOW even though I have full amount of oil in it. What's up with that?

 

The oil pressure sending unit represents oil PRESSURE and not QUANTITY. Regardless, the factory gauges are only general indicators of engine performance and nothing precise or accurate.

Look at the EVTM on Gary's site to see how they're wired, it's dead-simple:

Fuel Tank Selector & Gauges - ???Gary's Garagemahal

Electricity grounds to the engine block through the sending units, and bad electrical connections anywhere along the line can contribute to your problems as can worn-out sending units. I would replace both of them, make sure all electrical connections are clean, and go from there.

 

Success! I replaced the temp guage and all the guages work now (still have to see about the fuel though). However, I dont trust the temp. Is there an easy-to-install digital temp guage I can install that you're aware of?

 

Here's one:

2-1/16" WATER TEMPERATURE, 0-340 °F, SPORT-COMP DIGITAL