7 replies to this topic

[minimotivator]

hi
i would like to fit a smiths voltmeter to my mini it has two terminals on the back any idea how to wire this,i also have a smiths ampmeter that needs the same that has two large terminals thanks for looking.

[cooperrodeo]

I would advise you not to fit them yourself.

[bmcecosse]

You really don't need both. The volt meter is easy -one terminal to earth and the other to Ignition switched supply = white wire. The ammeter needs heavy duty unfused cables to be run up into the cab - possible reason for the earlier negative comment. If the cables are not very well insulated and perhaps rub through where they come into the cab - the potential (!!) is there for a nasty fire.

[dklawson]

I agree with bmcecosse. Later cars typically did not fit ammeters as that requires either an expensive "shunt type" gauge (which was not used by most car manufacturers)... or you had to run heavy gauge wire from the engine bay, into the passenger compartment, then back out again. It is indeed a safety issue. Ammeters were great when cars ran 22 Amp dynamos, not so great with high-current alternators.

Volt meters are easy to wire following the instructions bmcecosse gave.

[richard29593]

if you look in the Haynes manual there is a section on fitting accessories and the voltmeter is in there

hope this helps

[cooperrodeo]

All very true, but if you need to ask the question what the terminals are on a voltmeter and ammeter then .......

[dklawson]

All very true, but if you need to ask the question what the terminals are on a voltmeter and ammeter then .......

That is a good point and it is one we really didn't address in the replies above... not completely.

Ammeter:
Difficult to wire safely. The current flowing to/from the battery (excluding that going to the starter motor) must pass through the ammeter to indicate the amount and direction of current flow. This requires careful wiring alterations using the correct size wire with sufficient safety precautions both during the installation and for long term use. Though shown in the wiring diagrams for certain cars (various MGs for example), this is not a wiring change that should be undertaken if you do not fully understand how the ammeter works and the safety implications.

Volt Meter:
MUCH easier to wire. Smiths volt meters are NOT polarity sensitive. Like the later fuel gauges and temperature gauges they work by internal resistance heating of a bimetallic element. As such, you connect one volt meter terminal to earth (either gauge terminal). The other volt meter terminal is connected to a SWITCHED live source. As bmcecosse suggested, a white wire behind the dash will be a good source. There are other possibilities (many of the green wires) but you need to review the wiring diagram for your car to select a suitable one. (Have a radio? The switched power going to the radio is often easily accessible and suitable for the volt meter connection). Current draw is minimal and with only two wires to connect, the volt meter is easily installed at home by most DIYers.

[minimotivator]

hi all
thanks for your info on this subject i think i will wire up the voltmeter and just leave the amp alone.it just dosent seem worth the hassle.thanks again leigh