HELP! Electrical issue

[J Williams]

Here is what I have. My build ( https://67-72chevytrucks.com/vboard/...d.php?t=798538 ) I am building a 63 C10 and have run into an issue. When I put my gauges fuse in it takes a couple seconds after I turn the key to the on position (engine is off) and then the fuse pops. I have a new wiring harness (22 circuit universal Speedway Motors) that I have put in the truck. I pulled the gauge cluster out of the dash and pulled the gauges that require power (gas, temperature and battery gauge) then put the fuse in and then one by one plugged the gauges in. When I plugged the battery gauge in the fuse popped. I checked the resistance between the two wire connectors on the back of the back of the battery gauge and I had 0 resistance where I had resistance on the fuel and temp. So I figured I had a bad gauge. So I ordered a new gauge went out plugged it in, put a fuse in and then turned the key on. Smoke immediately poured out of my 100$ gauge I just ordered then the fuse popped. The engine is not running so I am confused at how that much power is going to the gauge to do this. The only thing I can possibly think is if the wire size is different and allowing too much to flow or if the old fuse panel some how had some form of resistor in it. Everything worked fine before the new wiring harness.

[ray_mcavoy]

How did you wire up the battery gauge using your new harness? Did you hook one side to positive and the other to negative? If so, that's the problem.

The battery gauges in these trucks are shunt style ammeters, not voltmeters. They need to be connected in parallel with a shunt wire so they can measure the current flowing in that wire. As you measured, the battery gauge has a very low resistance coil inside so connecting it up like a voltmeter (+ and -) results in a short circuit that blows fuses and/or burns out the gauge.

[Rickysnickers]

Is there a wire pinched or grounding out somewhere in the harness? As hard as it might be, you should probably trace the wires to that particular gauge and see what you find.

[AcampoDave]

This part that you said right here...."The only thing I can possibly think is if the wire size is different and allowing too much to flow or if the old fuse panel some how had some form of resistor in it. Everything worked fine before the new wiring harness."

I once used a larger guage wire across the radiator support. You know, the red one from the battery to the voltage regulator, and my ammeter was showing a huge charge and then it burned up later on. RayMcavoy is right on about the shunt wiring being parallel but in my case the wiring size was crucial too.
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[franken]

Larger wiring won't increase current unless the old wiring/connections was/were limiting current. If the old wiring was limiting current, there would have been heat generated. Its possible that redoing connections reduced resistance allowing more current, but the loads were meant to run on the original wiring, so new wiring still won't cause excessive current.

Current is drawn by a load, it isn't pushed by the source.

Regarding the battery gauge, I don't dispute the explanation above but have a simpler description. It simply reads the difference between two 12V sources. One of those sources is close to the battery and the other closer to the alternator. If the alt is charging, the V on that side is higher than B voltage and the gauge shows charge.

[Accelo]

The wiring size it critical, as it determines the resistance and thus the voltage drop. A larger wire size will not work unless the gauge taps are much further apart. I mean a lot further. The gauge is labeled Amps but it actually measures millivolts or 1:1000 of a volt. It is a volt gauge measuring voltage drop in volts. Full scale deflection is less than 1 volt. This circuit is know as a shut. Both sides of the amp meter are +, no grounds. Most convert the gauge to volts as a work around for this issue. I know the 67-72 truck guys do anyhow. I am unsure what is feasible for your 1963 truck. Do you still have the correct amperage fuses that are in the power to the gauge? Should be one on each leg. I thought they were 2A but I wouldn't trust that figure without looking it up.