[stackj]

Atsiii----

I just resolved a problem with the same symptoms you described with my 1967 C337B. I am going to paste text from a note I sent to a friend of mine below describing the issue.

If you want a little easier to read schematic (in my opinion, for what it's worth) go to the technical data page of this web site. Look under "Mitchell Instrument Cluster Replacement in 1967 C337". There is a link under that heading titled "Electrical System Schematic (PCX format). It is a redrawn diagram of the 38 amp Ford alternator system used in the earlier Skymasters. It applies to serial numbers 337-0526 through 337-0755.

Even if the schematic does not apply to your bird, the principle of the problem might.

Here is the description of what I did from the other note:

I spent a little time with our ’37 yesterday and a couple of days before that. I replaced several switches on the pilot’s sub-panel. Jenny had problems with the left (front) fuel boost pump being intermittent. I traced the problem down to the switch, and ordered replacements for both left and right. I was going to replace all the switches in the alternator field circuit while I was there but couldn’t locate all of them. I replaced the Run/Stby and Regulator Select switches, but it turned out the ‘GEN’ switch (Which turns the alternators on and off) was the bad one. I didn’t have a new one of those, but I was lucky. The switch has a split rocker and is actually two single pole double throw switches built into one. It only used the single throw function, so I was able to invert the switch, swap the alternator field wires to the opposite end and everything worked out fine. It eliminated electrical charging system oscillations I have had since buying the airplane. I’ll still try to get a replacement switch, but probably don’t really need to.

While I had the switch out of the panel, I measured the resistance of the contacts which had been used in the field circuit and found the resistance to fluctuate between 0.3 and 0.6 ohms. The unused contacts measured 0 ohms. I also disassembled and inspected the switch. The contacts which had been used were extrebely burned and pitted (lots of soot on them). The unused ones looked brand new. (Don't disassemble the switch unless you know what you are doing. They are not very complicated inside but can be very hard to impossible to reassemble if you spring the outer tabs too far apart.)

Hope this helps you out.

Jim