Non-working alternator
I have a Marlin kit car fitted with a circa-1975 Alfa Romeo engine (105). The alternator was not working when I bought the car – I don’t think the alternator was original to the Alfa engine; it is a Lucas 16acr – so I have fitted a recon replacement. I have no voltage output at the alternator terminals – it only has two wires going to it, large to main terminal and a small one. The alternator is spinning clockwise viewed from the front. The charge light is not on at all, even with the engine not running. Mike The alternator wiring on the Lucas 16ACR unit is quite simple and can be easily checked. The large wire going to the main terminal should be permanently fed directly from the battery; this is the feed wire and the one which will supply the charge voltage to the battery. The small wire should have a voltage when the ignition is on; this earths through the alternator to allow the ignition warning light to illuminate and the feed stimulates the regulator into action. When the alternator begins to put out a charge, this will prevent the ignition light from earthing through the circuit and extinguish the bulb.
The alternator does need to be earthed to the engine to correctly operate. You will need the ignition on to test it. First, remove the wires from the alternator and check if either has a feed when disconnected – the small wire may not be showing a feed when connected as it does earth out. If there is no feed to either, it would appear you have two problems: if there is no feed to the small wire, the first thing to check is the ignition bulb – it could be that simple; if there is no feed to the large wire, there must be a break in the circuit from the battery.
As this is a kit car there may be different options, one of which may be that the wire goes via a fuse; this would be a large fuse and may be a fused link within the feed wire. Remove the battery terminal and, using a continuity meter, check for any breaks. You should also ensure the engine earth is in good condition, although I would expect this to affect the starter if it was at fault.