[Nailheadforty]

Wiring up an idiot light for an alternator.
I have put an alternator in a pre a 1950 Oldsmobile. I would like to use an idiot light rather than a volt meter. I'm using the original ign. switch which is a three post switch. Post 1 is battery feed. Post 2 and 3 are hot when key is in the on position. (there is no acc. post on this switch) The starter is controlled via a push button which is activated be post 2. I'm using a one wire internal alternator. Its my belief I should wire the indicator lamp in series with the exciter wire. Hot feed to lamp (from post 3) ....lamp to exciter post on alternator. This doesn't seem to be correct as the lamp will turn on with the switch, but does not go out once the car starts. I'm sure someone out there has the help I need.
Thanks

[4 Jaw Chuck]

Found this, hope it helps.

Here's a quote from the site;

The Delco alternator is designed to operate using more than one wire going to the vehicle electrical system. In fact there were originally at least 3 wires. One BAT, one field and one sensing. Actually the field wire goes to the "idiot light" and then to the 'RUN' position of the ignition switch. The sensing wire either goes to the 'BAT' side of the ignition switch or the 'RUN' side depending on the application. When the ignition is in the run position the sensing terminal is energized with battery voltage and the field terminal is energized with a current limited voltage through the lamp. When the alternator starts charging, the field voltage raises and the voltage differential across the lamp reduces and the lamp goes out. The charging voltage is 'sensed' through the sensing wire and the internal voltage regulator regulates the voltage to about 14 volts.

[Nailheadforty]

Thanks for the info "Four Jaw" I also found some additional info in the archives, with "MadElectrical.com"

[AutoReWire]

Another diagram herehere