Spitfire Mk3 Ammeter Gauge Wiring

[Jonah]

Hello all, Has anyone fitted an ammeter gauge to a Mk3 Spitfire? My car has a dynamo and I’ve got a Smiths ammeter gauge ready to fit, I’m just not too sure about where in the loom to connect it 

[Pete Lewis]

you need it in the heavy brown thats the main feed battery to car

you may have a gauge, but it needs substantial wiring to carry all the current loads it is far safer and much simpler to 

fit a voltmeter, yes they show a different result but that can be wired into any white ignition wire and carries no high amperages 

pete

[Jonah]

Is the logic that pressure or volts is a much more useful indication of dynamo and charging health than flow or amps?

I’ve tried to keep the car as original as possible and have avoided an alternator conversion 

my goal here is to monitor the ability of the dynamo to supply power for the cars system, also there are no additional electrical load items fitted 

[Colin Lindsay]

1 hour ago, Jonah said:

Is the logic that pressure or volts is a much more useful indication of dynamo and charging health than flow or amps?

I’ve tried to keep the car as original as possible and have avoided an alternator conversion 

my goal here is to monitor the ability of the dynamo to supply power for the cars system, also there are no additional electrical load items fitted 

I had a voltmeter on my GT6 after I chickened out fitting the larger cables required for the current through an ammeter; you soon get to know how it's running. It'll be up around 13 or 14 during normal running, but once anything starts to drain the system, like headlamps or wipers, you'll see the needle drop. Once everything is turned off again it'll return to the 'normal' charging area, unless there's a problem.

[Jonah]

Thanks both I’ll go down the voltmeter route, is there a preferred place to wire it in?

I’m guessing that there’s not much voltage drop within the loom 

[Josef]

As Pete says, any switched feed will work. The radio position on the ignition switch is probably the easiest to use as it involves no changes to the existing wiring. 

[dougbgt6]

I had an ammeter on my GT6 VERY heavy cables required, it had to go in the end, the cables got worryingly hot. I have a Voltmeter now, it's not as good, by the time you've spotted something's wrong, it's too late.

I have, somewhere, a different sort of ammeter, the heavy battery wire goes through a coil which senses the current. Unfortunately it's a modern thing with an LCD display so I've not fitted it, yet.

Doug

[Jonah]

Thanks Doug you’ve summed up why I was thinking of an ammeter, I hadn’t t appreciation the overheating risk and I guess the dangers of taking heavy current cables through the firewall into the cabin

Like Colin I’m feeling more than a bit chicken now!

I bought the Smiths used gauge which came with a heavy gauge brown wire attached which waved at me like a big red flag 

ammeter will be on eBay shortly 

[NonMember]

3 hours ago, Jonah said:

Is the logic that pressure or volts is a much more useful indication of dynamo and charging health than flow or amps?

No, as others have said, the logic is that pressure and voltage are much easier to measure than flow and current, and are useful enough. My three all have alternators. The Vitesse has an ammeter (fitted by a previous owner) which is a great worry gauge as it swings across wildly when you flash the headlights. The other two have voltmeters (although one of those has randomly decided to show 17V whenever it's powered) for the convenience. They tell you if the alternator / dynamo has failed - not as quickly as the ammeter but the difference is less than the likely interval between you glancing at it.