Ammeter in 337G

[AV8ing]

Since this is my 1st post, a quick intro is in order: I'm an American ex-pat living in Europe for over 25 years. I am a fanatical pilot/owner/FAA A&P mechanic. Currently own a 1947 Cessna 140, a Cardinal RG and a Turbo Centurion. Recently, I have started to look after after a couple of 337s ...

I was hoping I might be able to get some help with a couple of issues on a '74 337G :

Ammeter - There's a small 1" ammeter over on the right side of the panel. I believe it was optional and is listed as p/n CM2626-N1 on the MM Wiring Diagram. The issue is that it appears to be inop - does not show any or very little indication. It tested ok with a multimeter and I traced the wires back to 2 fuses & shunt on the firewall, all seems ok.

Is this ammeter just useless or ?


Gear warning horn adjustment - The gear warning switches need to be re-adjusted. The problem, when ground testing for adjustment, no matter what the settings are with the switches, the gear horn always sounds when the green gear light is pressed. I went so far as to completely disconnect both gear switches and no change the gear horn sounds when the green gear light is pressed. I maintain about 10 SEP Cessna retractables and have never
seen this.
Any ideas why I can't simulate gear up with green gear
light ?

Thanks a 1,000,000 !

[CaptainRod]

I have a similar do-nothing ammeter. My mechanic is going to check it out this week. Will let you know what I find.

[AV8ing]

Rod - The ammeter is wired to a fuse block that is mounted on the firewall just above the battery (not to be confused with the 2 other fuses higher up and in between the voltage regulators). The fuses are then routed to a shunt that is mounted directly below the fuse block.

Is it possible that the shunt is INOP ? Anyone know how to test this shunt ?

[JamesC]

re ammeter I would check the connections along the cct length for minor corrosion as many of these systems have eg. annealed copper connectors onto aluminum which will eventually develop galvanic corrosion if there is any humidity. Just takes a minimal amount to increase resistance which would lead to a low ammeter reading regardless of the current in the system.
After some sanding/scraping and adding DC-4 could make a big difference.

re gear light, not sure re all Cessna models but in my R182 and 337 this is a push to test feature which like many of the panel lights will light or sound when pushed regardless of the status of the system (unless the light or horn has failed).
To adjust the gear horn microswitches, you could just mark the 15" MP setting with tape and then with the engines shut down and the cowling off listen for the switch click (easy to hear) as someone moves the lever past the 15" setting and adjust switch position using the two mounting screws as necessary BUT to be safe you would have to talk to an A&P familiar with the procedure in the 337/adjust as per the service manual.

[AV8ing]

"re gear light, not sure re all Cessna models but in my R182 and 337 this is a push to test feature which like many of the panel lights will light or sound when pushed regardless of the status of the system (unless the light or horn has failed)."

James - On your R182, try the push to test with the throttle pushed in or better yet, push the green gear light while at the same time pushing the throttle in, the gear horn will stop when the switch is tripped.

This does not seem to be the case on the 337 I'm working on and I'm trying to establish if it is normal and in that case, different than other Cessna gear warning schemas.

[JamesC]

Don't have my R182 anymore but on my 337 re the gear down light it illuminates and sounds the horn regardless of postn MP levers.

[AV8ing]

James - Thanks for confirming that point.