I had an odd problem last night and would appreciate any input on exactly what the problem could be.

After normal preflight (outside air temperature about 30 degrees F)and start up, I noticed a cyclical voltage drop happening about every 10 seconds. On my analog guage, the voltage would drop from about 13.5 to 12.0 and then bounce back. The drop would last maybe 1/2 second. There was a corresponding flux in the charge indication showing a discharge from the battery. I removed all possible load (radios off, lights off, all breakers pulled, etc.)from the system and it had no effect either on the amount of voltage drop or the rate of the cycle. I then turned off the alternator switch and left the battery switch on. Same symptoms. Next step was to turn the battery off and leave the alternator on. Bingo, during the "cycle", the voltage would drop from 13.5 right to 0 and then bounce back to 13.5 again. As the engine started to warm up, the cycle time expanded but the voltage variation never changed. The system, without the battery in the circuit, would drop right to zero for perhaps 1/2 second every so often. The timing of the cycle started at about every ten seconds when it first began and when I shut down, about 10-15 minutes later, it was at about every 45 seconds. The duration of the "down time" during the cycle did not change even though the time between events expanded.

Any suggestions on starting points for analysis? I sure do appreciate the guidance this board offers!

Thanks!

Roger Colby
N4800W 1976 114 (Serial #14120)
Johnson City, Tennessee