Ron:
Well, I went out to fly on Saturday; turned the master on, and no power at all. Well, my battery is about 6 years old, so I said that has to be it. Go back to battery box with volt meter in hand. Guess what; 12.7 volts. So all I can think of next is the master solenoid. Put volt meter on the battery side and 12.7 volts at the two small studs with nuts and wire, those are hot also with the master switch on, but no voltage on the side that goes to the front of the ship. My guess is that it is hanging up in the off position. After a few minutes of messing with it, it came on. I went flying, and then the next day I had it do the same thing on me.
Question is: would this be a master solenoid ready to go out, or could it be a bad wire or connection on the master switch, or a bad master switch or both???
I’m sure someone has had this same problem, and might be able to give me some advice.
Willis Cooke:
If you listen to the master solenoid and have someone activate the master switch you should be able to hear it activate. If it doesn’t click then something is wrong with the circuit. The power is always on the power terminal and the master switch grounds the ground terminal. If you ground this terminal with a wire and the solenoid clicks, but does not with the switch then there is a problem with either the switch or wiring. If the solenoid clicks but the output terminal is still not hot, then you have a solenoid going bad. The solenoid contact is a large copper washer that connects the input contact to the output contact. It can rotate so that the contact points change. If there is a burned spot or two on this washer it may contact in some positions and not in others. If this is the case, you need to replace the master contactor.
Editor’s note:
The fact that you still had 12.7V on both of the small posts, with the Master switch on, is a key clue. With the Master on, one of the small posts should be grounded, with a 12V reading only on the other one (and on the large post having the battery feed cable). This symptom tells me that your Master switch is not completing the ground path for the solenoid, so the solenoid is not operating. Willis has told you how to confirm this. If you are under the panel doing wiring and switch diagnosis, check all the screws on all the breakers and switches. You’ll probably find at least a quarter of them loose to some degree.