I am working with a 1965 mustang and have added heated seats.
The seat heater wiring does not have a latching circuit and is controlled by a SPDT Hi/off/Low switch.
In an effort to only allow the seats to be powered when the engine is running, I've added a relay to the control wiring that will have a fused direct battery feed for the heat load and "running only" source for the relay coil.
I thought of using the feed off of the alternator "BAT" output. My problem is that this wire is terminated at the hot side of the starter relay with the positive battery feed, so the coil would be always energized.
To isolate the battery from the Alternator output I was thinking of adding a diode. Not being sure of the alternator currents, I do not know how to accurately size this diode, an I am concerned about the heat it would generate.
Is there maybe a better TAP that I can use for this? Maybe the "fld" or "sta" from the alternator or something off of the voltage regulator that would be a better?