Does the starter relay 12v battery post need 12v?
its supposed to be a loop
battery to bulkhead to master splice RED
alternator to other bulkhead to ammeter Black then on to master splice RED
i.e the ammeter has a wire from the battery and a wire from the alternator In a loop.
colours used on my car may not be used on yours.... and mine has 2 bulkhead connectors, yours probably never did :)
Dave