Fitting an alternator with an ammeter

[Rory]

I am intending to fit a new alternator in place of the present dynamo, and currently have an ammeter in circuit.
Where does it go in the alternator wiring - in the wire between the A terminal on the Control Box and the starter solenoid?

[BTU268F]

Probably best to remove the ammeter as all the output from the alternator will pass through the instrument. 40-50 amps passing through the ammeter will overload the wiring and could cause a fire. Most ammeters are rated at 30 amps, way under the minimum output of the average alternator,

Better to fit a voltage gauge to show battery condition and general health of the charging circuit. Although with an alternator it will always be charging the battery, even when the car is ticking over.

The wiring loom will need changed for the voltage gauge, I'm sure someone on here could share the wiring diagram.

[bmcecosse]

I disagree - I had an alternator and ammeter for years and years. It rarely ever showed more than 10 amp charge - just for a very short time after starting. Remember -it only carries the current going in/out of the battery - not the output of the alternator, which is supplying the lights etc directly. I'm sure you already have good thick cables on the ammeter, and make sure they are well protected where they pass through the bulkhead - because of course they are not fused in any way. The ammeter wiring stays where you have it now - except you may chose to delete the Control box - or retain it as a handy connector block - in which case be sure to join A and A1 together.

[IslipMinor]

Whilst it is certainly true that the ammeter shows what is going into the battery, and not the total output of the alternator, it also shows what is going out from the battery, which with additional items like heated screen(s) could be very much more than 30A. If the engine is not running, or stalls for some reason the discharge could be 40A+, so I would always fit an ammeter to suit at least a 50A working range. Obviously the wiring from the alternator to the ammeter must be for the rated output of the alternator.

A 'modern' replacement (A127) for the very common Lucas ACR range can be anything up to 75A output (~£50/60 on eBay), and shows a 40A instant charge on start-up, but drops back very quickly to a few amps if the battery is in good order.

The ACR and later equivalents have 2 x 35A Lucar output terminals, so running 2 smaller, flexible cables to give the correct total capacity is not a problem (2 x 65/0.30mm cables give 70A capacity) - the table below shows the capacity for common cable sizes:
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The whole area of ammeters does come with a very serious health warning, as Roy has mentioned before. The whole circuit is unfused, so great care must be taken with connections and protection of the cables, especially when passing through the bulkhead. As part of the restoration I added a number of additional circuits into the loom, before getting it recovered, and made a second loom hole through the bulkhead, using the same grommet and fixing as the original - gives an 'original' appearance and keeps all the additional wiring together, including the alternator to ammeter to battery cables.