My 1959 180 has a mystery 25 AMP circuit breaker under the panel just below my left knee. It seems to act as a Master Switch when pushed in, the usual devices power up as if the real Master switch was turned on. I have a separate panel mounted Avionics Master switch. I think I've always run with this breaker pushed in how ever I've had 2 recent experiences where at startup the JPI 930 shows no alternator input, amp and voltage readings red and at the bottom of the scale - upon checking, that 25AMP breaker has popped out. Push it in and all's fine.

When I raised this question on the Airworthy Forum, one poster thought that many years ago, the Comanche had just one master for all aircraft electrical loads. As Avionics developed, the Avionics Master was added (factory or ?). At this point someone ?? felt this add'l beaker was needed to give add'l master circuit protection.

Anyone care to chime in on this one ?

Thanks,
Gary
Granbury, TX
5849P

Gary,
It would be a bit of a scavenger hunt if we had an answer as to how all the different Comanches have been rewired over the years. 25 amp is a little small for a main master breaker. The only thing I can think of is that that breaker somehow is backfeeding the master solenoid causing the "master" to be on. Original aircraft had a 35 amp generator, and a 25 amp gear breaker. The gear breaker was mandated to be changed to 30 amp by SB, and most aircraft have since had at least 50 amps on the charging side of the system whether it be generator or alternator. I'm going to guess this breaker has something to do with the charging circuit, but not in a good way. I would try to figure out what is wired to the wrong side of a post or has a crossed wire before you find out the hard way with lots of smoke coming out of wires or expensive avionics.

Zach