I have restored a 1942 LA and is complete except the ammeter will not show charge. It will show discharge when I turn the light on but will not show charge. I have the downloaded diagram for the wireing and have wired it exactly. The gen is rebuilt and charges 7.5 v0lts but not on the ammeter. I have checked all wires and terminals several times and the shop that rebuilt the gen came and tried to help me to no avail. This is a three brush wired with a light switch. We have bypassed the switch and tried it that way and I even replaced the ammeter. Still nothing. HELP if you have any suggestions.