OK.... Today I was out trying to get my 74 cleaned up & put some stuff back together in the interior.

I had a problem w/my gas gauge months ago & took everything apart to try & figure it out. I got a second gauge cluster (from a 78~80 Chevy) from Jonboy to use for setting up some aftermarket gauges. My search for the 'right' size gauges has been a slow one so I decided to see what would happen if I swapped the gas gauge from the extra cluster into mine. It works..... I guess the problem was just the gas gauge all along.

So while I'm getting everything cleaned up to put back together, I decide to also use the voltmeter from the extra cluster instead of my current ampmeter. After playing around, I figured out what terminal on the back of the voltmeter was ground & which required power. I tested it using some leads hooked to my battery & verify it works (~14v on the gauge vs. ~14v on my test meter).

For the installation, I removed the 'clips' that connected the ampmeter to the printed circuit to avoid any accidental contact. I wired in the voltmeter using the ground & power for the clock. I switched the power lead from the 'batt' (constant power) on the fuse block to an ign fused terminal, then connected it to the voltmeter & then did the same for the ground.

I went to start the truck & the voltmeter doesn't do anything. I verified the ground & power both were good. I decided to remove the voltmeter & re-check it using the same method I used earlier. It doesn't work now. If I switch the leads around, I can get it to peg out @ 18volts but when disconnected it goes right back to zero.

What am I doing wrong?

It's hard for me to follow the sequence of events in your description of wiring the gauge. But, I suspect your power source (clock) is the reason. Your power would need to go from the fuse panel, to the pos terminal of the gauge, THEN to the clock (not to ground).
If that doesn't work, you may have one of the "spurt" clocks, that use a spurt of voltage every 90 or so seconds. If that is your style of clock, the gauge would only work once every 90 seconds or so.
A volt meter uses almost no current, and can be safely wired to any accessory, and something besides the clock should be used, because the clock is "live" all the time. A better circuit to tap into would be turn signal, or heater circuit IMHO. Just remember to wire the circuit for the gauge, through the gauge.
hope I've helped

It's hard for me to follow the sequence of events in your description of wiring the gauge. But, I suspect your power source (clock) is the reason. Your power would need to go from the fuse panel, to the pos terminal of the gauge, THEN to the clock (not to ground).....
Sorry if my post was confusing. I only used the existing wires for the clock.... I did not wire the voltmeter in series w/the clock. The clock was not hooked up & does not funtion.

I first verified that the ground wire intended for the clock was functional.

I then did the same for the power wire & realized it was always hot. I moved the power wire to an ignition fused terminal on the fuse block.

I then connected the ground & power to the appropriate terminal on the back of the 'new' voltmeter.

For connecting, spade terminals were crimped & heat-shrunk to the wires. Both meters used nuts to secure some sort of junction strip on the back of each gauge. I took the 2 nuts off the ampmeter & used them in conjunction w/the 2 already on the voltmeter, securing/sandwiching the spade terminals in between).

I hope this makes my installation procedure less confusing.

You might to hookup closer to the batt farther downstream. It sounds like you are hooked to a source past the ign sw. You will need to get closer to the battery and then it will show voltage.

You might to hookup closer to the batt farther downstream. It sounds like you are hooked to a source past the ign sw. You will need to get closer to the battery and then it will show voltage.
I don't think you can get much closer than this.... I hooked it directly to the batt (the correct way) to see what the heck was going on & I get nothing. If I swap the power wire to the 3rd terminal on the back of the gauge, the needle sweeps over to 18v & stays..... when I switch the power lead back, it goes to zero.

I originally tested the gauge this way & compared it to my test meter so I know my power/ground terminals are correct as far as 'what's what'.

It should show system voltage hooked to batt like you tried. Are there any markings on the terminals. Sounds like you have three. Can you post a pic? maybe someone that is familiar with that model can help.

This is one for the books . . .....

After reading your reply, I went to pull the gauge out & get some pics. I got the gauge out & decided to try it again vs. the test meter @ the battery.

I was preparing for the test & wanted to get a better bite w/my alligator clip, so I removed one of the nuts from the 'power' terminal & put it back on the 3rd 'un-used' terminal (opposite terminal, not the ground) so I wouldn't lose the nut.

I hooked up the pos/grnd & violia..... the gauge read ~13v & was consistent w/my test meter. I tightend that nut securely to the 3rd terminal & hooked up my jumpers to the wiring in the dash & the gauge now works in the truck.

Apparently it wasn't getting a connection after I removed that nut from the 3rd, un-used terminal. The million dollar question now is what the heck is the purpose of the 3rd terminal?

Thanks for the assistance. Sometimes all it takes is someone helping you think differently to realize the solution :c2: !

There's one other weird thing occuring. The original reason I was out working on the truck was to swap in a newer gas gauge. I got the 'new' gauge in place & although it does seem to work (hard to tell since the tank is actually full), it pegs the full mark when the ignition is hot..... I mean 'pegs' like you're hammering the throttle in a drag race.

Any ideas on this one? Thanks again..... Scot.

If you have an oppen circuit between the sender & gauge the gauge will go over way beyond full.

Somethings not right. It reads empty when the ignition is off & goes immediately to full when the ign is on. Before (w/the original gas gauge), it just stayed past the full mark all the time.

Sounds like the wire to the sender is disconnected between the guage and the sender or the ground from the sender to the frame is disconnected the fuel tank wont ground itself more often than not so there is a wire from the sender body to the frame. If the guage reads empty when the key is off and pegs full when it's on the guage is working but the sender isn't causing the resistance for the guage to read. Just an idea.