The Stovebolt Site Forums The Shop Area The Electrical Bay proper way to wire amp gauge

I need the proper way to wire my amp gauge. I have a 36 gmc with a 4.3 vortec engine and want to use the OE gauges. I have everything working but I am uncertain on wiring the alt. Can anybody help with a wiring diagram or written instructions? Thanks for any help with this.

1. Battery cable to starter.
2. Starter to Ammeter terminal. (can use a fuse on that wire)
3. Other Ammeter terminal to alternator, fuse panel, everything else.
4. Option: use volt meter instead of Ammeter. Wiring will be different.


I Assume you now have 12V Negative ground. No guarantee a 1936 Ammeter is OK for 12V.
Some orig gauges will need voltage reducer, as you know.

You seem to have asked 2 questions. Please clarify so we can answer more clearly. Are you just wanting to know how to wire your ammeter (amp gauge)? Or are you asking how to wire your alternator?

I was just asking for a hand drawn wire diagram for the amp gauge. I have had the gauges redone for the 12v system. Just not sure what wire went where. hope this clears up the confusion I'm sure I can use the written directions from bartamos. thank you for them.

Some simple diagrams. And if you don’t want the high amp going into the dash put a shunt in sized correctly.
And run smaller wires to gauge. Note the smaller wires should have a fuse on both as well not pictured. This will solve the safety issues if shunt failed
Which is like super rare

So would I use an actual "fuse" or a fusible link? dose it come in different amps to melt? The same as wire gauge? The gauge does have a shunt on it. Would I put the link out by the alt? or under the dash? Both wire's ? inlet and outlet?

You can use a fusible link or an inline fuse on the "in" to ammeter. Fusible links are sized 4 wire gauges less than wire gauge. Example: 10 gauge wire, you buy a 14 ga fusible link. A fusible link is a piece of wire with special insulator. Wire will melt before insulator. It is not really necessary to have a "fuse" there as the ammeter measures current, doesn't draw. But theories abound so use a "fuse" if you wish. As you see the "out" (not using "input or "output" terms), goes to the fuse panel. So most components are fused there. Other components on the out side, like headlight switch, have a built-in fuse. Nothing to worry about, just wire it up. You won't be Fireball Roberts. 10ga or larger is usually recommended for in/out. Search internet for a bunch of info and sort out what most say to get a consensus and be comfortable with what we say.

Re fuse or fusible link: The former is easily replaceable. The latter, not so much, requiring splicing in a new one.

I don't remember ever seeing a fuse nor fusible link between the starter to ammeter, so if that's something you don't want to fiddle with I'd say everything will be Jake for you.

When was the last time anyone saw an aftermarket amp gauge for a car/truck that had an external shunt like HCB3200 shows above? It is a good idea for less current flowing around up under the dash.

Ammeters have internal shunts usually. These can be supplemented by an additional wire. These things are done to "recalibrate" an old meter to read/handle an upgraded charging system. It's all about the size of the shunt/resistance (big copper buss bar or big wire 'jumper"/bypass/whatever) to get the right voltage drop/small (millivolts) sample current for the little old meter movement. In our case with older trucks we only need to see charge/discharge, not some exact value. As you start the motor, battery gets lowish, so you see plus on the meter for awhile. Showing alternator is replenishing/charging battery and running other things. Then goes to "zero" (needle biased to plus side for battery holdup) showing battery is filled up and alternator is running all. If you see negative after driving awhile, either you have too much load and battery and/or alternator can't keep up or something is wrong with battery or charging system....or meter. Battery voltage will drop and won't start motor. Negative reading on ammeter can also indicate the wires are on the wrong terminals.

The voltage regulator is to handle it all for you.

The battery was only to start the motor. Now-a-days it runs clocks, security, radio memory, etc. when motor is off.

Stewart-Warner used to have a separate Marine Gauge section in their catalog that included External Shunt Ammeter Gauges. A Internal Shunt gauge on a boat could require very long and very large wires, which would be expensive and dangerous.

60 - 72 Chevy Trucks used External shunt gauges, but they didn't use an actual External Shunt. They utilized existing harness wire to serve double purpose as both charging wire between the Alt and Battery and also as the Shunt.
The first image is an actual External Shunt. The 2nd image shows the segment of the 12R that serves as the Shunt as pointed out in Blue. The 18B with fuse and the 18 B/W with fuse, connect through the bulkhead connector to the dash External Shunt Ammeter gauge.
The 3rd image shows 3 Internal shunt gauges, even though the shunts are mounted on the back of 2 of them. Both are 60 Amp gauges and would generate too much heat if the shunt were inside the gauge. The small Ammeter is a 20 Amp and does have the shunt inside the body of the gauge.