Wiring Instructions for Speedwell Powermaster AMP Guage

[62Countryman]

Does anyone have the instructions on how to wire a Speedwell Powermaster AMP gauge? The gauge has to main terminals (to measure amperage) and 2 wires that lead into the body of the gauge (Red and Black wires). I am almost certain that the Red and Black wires are used to light the 2 lamps located inside the gauge.

[Tim]

It needs to go in series with all of the power supply to the vehicle (except the starter motor, normally). How you do that depends on the wiring. Its easier on an early car with the push starter, you need to put it in the heavy brown wire which runs from under the floor to the voltage reg. It gets trickier as the wiring becomes more complex.

Tim

[dklawson]

I have no experience with that particular ammeter. However, I can make some general suggestions that go along with those made by Tim.

As mentioned, the ammeter is installed in series with all the "normal" current flowing through the car excluding that used for the starter motor. You can see a typical Lucas scheme for an ammeter by looking at the wiring diagram for the Triumph TR2/TR3 (link below).
http://www.advanceautowire.com/tr24a.pdf

An alternative to that scheme is to locate the terminal on the solenoid where ALL the brown wires connect. Remove all those wires and join them to one of the ammeter terminals (indirectly via a very heavy gauge extension wire). Run a second heavy gauge brown wire back from the remaining gauge terminal to the solenoid terminal where all the brown wire were removed. Turn on the headlights and observe what the ammeter displays. If it appears to be reading backwards (showing charging when you know the battery is draining) switch the two ammeter connections at the gauge.

It should go without saying that you should not use the Ammeter on cars with alternators unless the ammeter and its wiring are rated as high as the possible output from the alternator.

[Tim]

You need to bear in mind that should the wire passing through the gauge short out against anything, the entire current will be trying to find its way to ground, which will be a bad thing.

Tim

[dklawson]

You need to bear in mind that should the wire passing through the gauge short out against anything, the entire current will be trying to find its way to ground, which will be a bad thing.
Tim

Very true. I have several ammeters in my collection of gauges and I only briefly ran a +/- 30 Amp one on a Triumph where the car still had the dynamo. As soon as I replaced it with an alternator I switched to a voltmeter instead. I have always been nervous about heavy gauge wires passing through the firewall.