After many months and a lot of research, my electrical system is now very stable and reliable. I thought I would share what I have discovered and I hope this will help many of you with your electrical problems.

Two years ago, I purchased a 1973 337P and before I could get it home it began giving me fits with its charging system. Luckily, Gmas was having one of his seminars in the Sacramento Area and I was able to explain the problems I was experiencing and he gave me a list of items to checkout. Starting with a new battery and contactors the problem still existed with me unable to keep the rear alternator on-line, so as GMas has described, we looked into the drive coupling on the rear alternator and found that the Lord Coupling had given up and I replaced the coupling with the Continental Coupling. While I had everything apart I took the opportunity to have both alternators overhauled and the voltage regulators checked. Keeping my fingers crossed I hoped that this solved the problem, but no such luck.

Next we discovered that the Over/Under Voltage Sensor needed to be replaced and again I was optimistic that the problem would be solved, but we still had an imbalance between the alternators and pulsing voltage in the system. So, it was on to the diode board on the front firewall, and all of the diodes were replaced and the board circuits checked. I won?t go into detail on how to check and replace the diodes as Gmas has written numerous articles on this subject, but I thought we were running out of things to check or replace, so we had to be getting close to the end of the tunnel, but the same problem persisted. Then it was on to new circuit breakers and field switches and this finally got the system stable and working, but that?s not the end of the story.

After about 3 months all of the problems came back, the alternators would not stay on-line and the voltage pulsing was back. I knew I had replaced or repaired every part Cessna had put into the aircraft at the factory, so what was left to fix? I started calling the different manufacturers of the components and getting their feedback on the problem. After explaining all of the parts that were replaced one thing started to become apparent and that was the aircraft wiring. This system is so sensitive to changes in resistance that the ship?s wiring has to be in top shape.

With this in mind, my mechanic and I went though every wire that was associated with the charging system looking for possible areas where the resistance could have changed. We found that in my case, the ship?s wiring was still in excellent shape, so all we replaced was about a two-foot section of the wiring on the rear alternator. The next thing we did was replaced every connector and or their pins in the entire charging system, making sure that every connection was crimped and soldered. The biggest deal was making sure every connection was soldered, as this will keep corrosion out of the joint which in turn will build up resistance. This sounds like a lot of work but it is just time consuming with very little expense in parts. After all of this was done the voltage was stable out to a hundredth of a volt and finally the voltage regulators could be set and forgot about. So what I have learned from the whole episode is that the components in the circuit cannot do their job if the wiring is not up to the job of flowing a pure current.

In conclusion, if you guys just change out parts in the system without any regard to the wiring, I think you will be only putting a ban aid on the problem without really fixing the problem. But in my case, after about a year of work, I finally have a system that is very stable and most of all reliable. I want to thank everyone who stood by me during this ordeal, especially Gmas, because without your help I would have given up on this project.