When I did a conversion to a 66 gauge cluster some 17 years ago, I used a dedicated wire and a 10 watt 18 ohm resistor and a fuse holder with a 2 amp fuse. I tried several ohm ratings and settled on 18 ohms which made the gauge responsive but not too responsive. The gauge will deflect fully with less than an amp across it and they will fry if the battery main terminal is degraded or disconnected...it was one bad design, but I safeguarded it. Still working great years later. The retro voltage gauge though is a nice alternative that I don't think was available 17 years ago.1966 V8 (302ci with MSD ignition and coil - AGM battery, stock alternator)
Just noticed that my ammeter needle never moves. I can switch on the AC and the headlights, and it still doesn't move, whether I'm idling or at speed.
Shouldn't that needle deflect at least when I engage something electrical?