Bought a C-65 tach gauge cluster with Ampmeter but need to convert to volts???

[BigHemi353]

Well, I scored a Tach cluster today out of a C-65 grain truck. Very excited since I've been looking for one for about a year now. 80lb mechanical oil pressure gauge, tach with the fuel gauge under it and vacuum gauge that I can hook to my vacuum pump on my cummins just because i can.  Looks exactly like this except it has the ampmeter instead of the voltmeter in picture. (stole a pic from captkaos from google)

 I know that I CANNOT just plug it in and go since this will burn up my wiring harness. My question is can I install a voltmeter gauge(from my 78 k20) in this cluster and remove the pins from my cluster's main electrical plug to get this to work? To completely bypass the printed circuit and hardwire the volt gauge in order to keep my wiring harness from burning up? Im thinking that this would be exactly the same as putting aftermarket gauges in this cluster but you guys are the experts, not me! Also, I'll be using a 85 K-20's wiring harness but I'm thinking that wont be too much of a problem other than swapping out a few pins here and there. Thanks alot guys!

[Captkaos]

you won't be able to swap a Volt gauge in the AMP slot, you can potentially swap everything you have to a Volt setup, but the printed circuit would be the issue.  A lot of rewiring will be in your future though to get it to work.

[BigHemi353]

So basically, your saying that the ampmeter circuit board is completely non compatible to a 85's wiring harness? Its not the gauges themselves but the ampmeter era printed circuit? I never thought about swapping the stuff I want to my 85's cluster or the 78 cluster that I have. I will look into that tonight.

[BigHemi353]

Well, Thanks Chris. I figured out what I'm going to do. I have a 78 tach cluster that I'll swap the tach/fuel gauge. I'll probably sell the 78's tach and fuel gauge later on for someone else to use. All I will have to do is figure a way to wire up my fuel gauge(either run small copper wires to my printed circuit and attach them somehow or hardwire the fuel gauge).  Since I will be removing the little fuel gauge from the 78 tach cluster, I can put my fancy vacuum gauge in there so I can be sure my vacuum pump is good. As for my oil pressure gauge, I will run the original 60lb for the mean time until I can find a electric 80psi gauge out of a 80's model 6.2l diesel truck. I believe i can put the diesel oil pressure sending unit on the cummins and let the gauge top out(since the cummins motor should run somewhere from 40-80psi, give or take a few).

Seems like a lot of work for just a little mod but hopefully it'll be worth it.

[Captkaos]

The ampmeter wiring is complete incompatible with Volt wiring. 
Ampmeters measures current flow and everything is fed through it from the battery to get an accurate reading.  Ampmeters are wired in series in a circuit
Volt meters can just be tapped into the system anywhere and measure the voltage output. Voltmeters are wired parallel in a circuit.

Either way you approach this, you are going to to be doing some rewiring of the truck.

[BigHemi353]

What will I have to rewire? They way I see it is every gauge is basically in the same place if I use the 78's cluster housing and my 85's printed circuit. Volt will be in the same position as well as they oil pressure and temperature gauge. Only problem will be the connecting the fuel gauge to the printed circuit or hard wiring it.

[Captkaos]

I think I typed this up and forgot to post it and didn't see your new info.

If you swap it to a 78, those are you only issues.

[BigHemi353]

Alright, Thank you very much. After I finish it I will post pictures if it comes out like I want it to.