Original Amp Meter External Shunt?

[74Corvette]

I am working on a 71 GMC pickup. When I bought the truck it came with new aftermarket wiring. Wiring works fine but what I am trying to do is get the original amp meter to work. I know the original gauge is an external shunt style meter and as I understand it is basically measuring the voltage drop across the shunt. Problem is I am pretty sure I do not have the shunt anymore. So what exactly is the shunt? After studying the engine bay wiring diagram the only thing that makes sense is the fusible link. The wiring harness I have is a painless system, I don’t know what model, and it has a large main fuse, which I am guessing is the modern version of a slow blowing fusible link. The amp gauge is brand new and functioning. Any ideas on what I can do to wire up the amp meter?

[john]

Here's a pic. the two 4 amp fused wires are your ammeter circuit. Welcome to the board.

[74Corvette]

Hi John, thanks for the reply! This makes more sense than the fusible link I came up with. Could I just splice in the fuse wires within my current wiring harness? If so, where would I get the fuse wires from? Forgive my inexperience on this but, do I need to track down an old harness and salvage them, or is this a replaceable item available at local parts stores? I can’t imagine I need to replace the whole harness.
Also I just want to add this site and its members have saved me huge time and dollars over the last couple years during my resto, thanks for all the help.

[VetteVet]

The key to the battery gauge is where do the battery gauge wires connect to the battery and to the alternator. one wire must connect near the battery and the other wire must connect near the alternator output. Then there has to be a connection between these two points. This connection is called the Shunt.

AS you can see in the diagram, the alternator output wire is connected to the junction of the positive wires that feed the truck circuits. The shunt wire is the battery connection between the battery, and the alternator, and it also serves as the power wire from the battery for the truck circuits in case the alternator fails.

Some guys will just run the alternator output wire straight to the battery positive post and then wonder why the battery gauge won't work. The reason is because the output wire becomes the shunt and the battery gauge wires are no longer connected between the ends of the shunt. If they connected the alternator side fused wire to the alternator output and left the battery side wire at the battery, then there would be a shunt and the gauge might work. It was calibrated by the factory for size and length of the shunt and the fuse wires to match the battery gauge so it wouldn't be very accurate. It only shows charge or discharge anyway so that's not much of a factor.

The fuse wires are just 18 gauge AWG wires with a 4 amp fuse inline and wired to the cluster plug at pins 1 and 12 on the plug.

Here is a thread that should help.
http://67-72chevytrucks.com/vboard/s...d.php?t=581719
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[VetteVet]

The Shunt wire is a 12 gauge red wire about 6 feet long and runs across the top of the radiator and connects into a soldered junction in the harness with the regulator red wire, the alternator red wire. the supply wire that goes to the firewall block and into the cab and the black fuse wire that goes to the cluster plug.

Here is a picture of the junction on my truck.

[74Corvette]

Thanks for the info on this, this is very helpful. It is a little cold right now but in a couple weeks when it warms up I will give this a try. Thanks again!