Hi Martin. If you are using a digital voltmeter, it might be giving false readings due to the amount of electrical noise. Try one with an old fashioned needle and see if it gives the same reading.

I don't know why your ammeter is showing a discharge, but you might want to double check that it is wired the right way round. When you turn on the ignition the needle should move towards the discharge side by a couple of amps, assuming the points are closed. Alternatively, try rigging up a temporary switch and headlamp bulb downstream of the ammeter and see if it moves towards discharge when the lamp is switched on and drawing current. It's simplest if the engine is stopped for this test.

Apologies if this is telling you stuff you know already - it's always hard to judge things from just a message board !

Location: New Forest

Hi John

Have no fear about insulting my electrical knowledge. I am the man who many years ago scored MINUS 8 in my uni electricity and electronics exam!

I'm pretty confident that the ammeter is wired correctly. When the ignition is switched on it show a pulsing discharge as the electric fuel pump does its stuff, so I take it that anything that it says is a discharge is just that.

The meter is a cheapo digital job and I am aware that they can be affected by "noise". I do have and antique Avo Minor - I just need to cobble it to accept a modern battery!

Location: Herefordshire, with an E not a T

Hi Martin

I partly pass on the latest!

An AVO Minor may not need batteries to measure volts and current.

Modern meters measure the radio radiation from the ignition. For work on old cars with no elctronics a resistor of 1000 ohms or much more and/or a capacitor, maybe even as big as an ignition capacitor, across the terminals may eliminate the noise. Others who dabble more often will hopefully advise more optimum values.

Analogue meters are very easy for amateurs and not so amateurs to cook when unexpected voltages and currents and charged condensers are encountered. AVOs are now somewhat precious.

Bob Culver

Location: Auckland