1966 c10 stock amp gauge

[sampsonsmetal]

Hello-
I was told that I can't use my stock amp gauge with a one wire alternator. The alternator puts out more amps then the gauge can handle and cause a fire??? I know I'm not the only doing this please help.

Thank you, Tom

[ray_mcavoy]

The stock battery gauge is an external shunt type ammeter. That means that the vast majority of the charging system current flows through the truck's charging system wiring just like it does in a truck without gauges. The charging system wire that runs from the horn relay across the radiator support to the battery serves as a shunt for the ammeter. Only a small fraction of the current actually goes through the gauge movement itself (it only takes about 1.5 amps to peg it full scale).

You can upgrade to heavier gauge wire in the charging system to safely handle more current. That will effectively lower the resistance of the "shunt" and therefore keep excessive current from flowing through the stock ammeter. However, it will have the drawback of making the meter less sensitive to small amounts of current flowing in the system.

In any case, I would highly recommend adding some 4amp inline fuses to both legs of the ammeter wiring just like GM did in the 67 & newer trucks. Locate one where the black wire with the white stripe attaches to the bus bar on the horn relay. Locate the other fuse in the black wire that attaches to the large batt stud on the starter solenoid. Having these fuses in place will make the stock ammeter very safe. A short to ground on either wire or excessive current will blow one or both of those fuses long before anything gets hot enough to start a fire.


Edit: I forgot to mention one important fact when changing / upgrading the alternator and using the stock battery gauge. That is, the output wire of the new alternator needs to be connected to the bus bar / junction point on the horn relay (same as the stock alternator). If you were to connect the alternator output directly to the battery (or some other point in the system), it will bypass the ammeter's "shunt" wire and prevent the meter from correctly indicating charge or discharge conditions.