They are notorious for causing issues and starting fires Steve. May be ok if someone knows what they are doing. I replaced mine with a volt meter, after a bit of a meltdown. If I recall it goes in series in the main feed from the starter to fuse box and light switch.
FB ute fixer upper, EK van on rotisserie
getting my FB ute on the road
EK van on rotisserie
For use with generators really.
They need to be wired so that all output from the generator +ve goes in the negative side and all circuits getting power connect to the +ve side of the meter. On FB/EK with generator and original wiring this is using the power input on the rear of the headlight switch ( can't remember if its red or brown) to the negative on the meter and the +ve on the meter goes back to the headlight switch. The alternative is to wire from the regulator box. The reason they are reputed to cause fires is because all the cars current has to go through them and if there are poor connections that get hot, or wire of too small a diameter has been used, the wire gets hot and melts and then all of a sudden it earths out and on this circuit there is no standard fuse. A fuse of 40 amps in line with the power circuit sorts that out when used with a generator.
For an alternator that produces 50amps+, a voltage guage is simpler to install and tells you what you need to know. A fuse on the alternator output is not recomended because if it blows, your alternator is toast imediately.
Hope this helps and is correct.
Easy way to test it is to wire up a heater fan or a headlight or two in line with either the positive or you could use the negative wire from a battery. Only one polarity through the meter and the other to the load. Don't wire positive to one side and negative to the other on the meter or you will discover fire very quickly.
I can tell you what happens when things go wrong. I had an X2. It had the ammeter. The ammeter terminals (uninsulated at that) were perilously close to the rod from the wiper motor to the RH wiper crank. It was night, and hurling down with rain. I turned the wipers on. Once per wipe cycle, the vehicle lights dimmed, and once per wipe cycle, there was a bright flash from under the dash.
The wiper linkages briefly shorted the battery to ground.
Moral of story: the "lay" of the wiring connections is vitally important.
But otherwise, exactly what Brett says.
ETA - with one minor correction: the ammeter is connected in series with the wire that goes from the voltage regulator B+ terminal to the starter solenoid B+ terminal, that is, the big fat red wire.
