I'm working on a 48 with a 12V neg. ground conversion. When I got the truck, it had a nice Tach, I think it's a Sun although there are no markings, but it's the usual kind of thing you would get at aftermarket places like Summit. None of the wiring is connected, although it once was, with just bare stripped ends. The color choices are red, green, blue, and white. So I'm thinking one is for power, one for ground, one to connect to the coil plus, and maybe one for the light in the housing? I took it apart but there's no markings on the inside as to connections. Anyone know if there's an industry-standard color code or guide for these that I could try before going trial-and-error? One other check -- my stock ammeter is toast, so I'm putting in an aftermarket ammeter. The generator is 12V with three leads, plus, minus and what has to be a ground, bolted to the case. The ammeter wiring should be: one ammeter terminal to the battery positive terminal, the other ammeter terminal to the generator plus terminal. In other words, the ammeter in series between the battery plus and the generator plus. Correct? Thanks.

 

A simple and quick google search for 'sun tach wiring diagram' finds several photos.

 

I would not recommend putting in a shunt-type ammeter as you have described. Lots of potential for making smoke. A voltmeter is low-risk and much simpler to add in. The three wires from the generator are Field, Armature, and a Ground. The armature lead is the output.

 

Agree, plus a voltmeter gives you a better idea of what is going on in the whole electrical system, not just the generator/alternator. The voltmeter will tell you if your system is charging and will also let you know how much power the battery has.

 

O.k., Voltmeter it is. On the Tach: if it were red, white, black and some other color for the coil, I would have done it already -- that's the typical color scheme for all of the tach.s I've previously installed. It's the blue-green choice that has me scratching what hair I have left. Think I'll go with green as the ground, on the perhaps thin logic that green for ground is standard for residential household wiring. No big deal if it doesn't work; maybe the reason it was disconnected when I got the truck was because it was already blown. But I have the feeling that whoever worked on it before, disconnected it in an effort to isolate a gremlin, one which I apparently have either corrected or bypassed, because everything else is working now. I think. So far. Thanks for the help, gentlemen.