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Add me to the confused list as I have been trying to follow this and got utterly lost. At the risk of stating the obvious, and knowing this has probably been talked about, have confirmed that the battery is in fact healthy??

I'm confused as to why your A&P is "advising" you to replace parts, but at this point having followed the entire previous thread and made a good faith effort to give you some information to trouble shoot with, my conclusion is that you're massively out of your depth and it's only going to be by a stroke of luck that you stumble across a solution.

Get your A&P, or a better one, out to your plane and just have them fix it. This is a very simple problem and would take someone who knows how to actually use a voltmeter less than 10 minutes to diagnose.

I'm not going to jump on the band wagon of the know-alls. It sounds very likely that you are having some intermittent electrical issues on your starting system. I can assure everyone here, that I have experienced this frustration across all types of mechanized transportation, to include airplanes.

Solenoids can be a real pain to troubleshoot because the contacts burn and they "don't work" on random occasions. Starter motors can also have intermittent failures (in the old days, remember whacking with a hammer?)

Solenoids (relays) are relatively cheap and are a known item to fail. Wiring and connections are also a known intermittent fail item. All these things can drive one crazy trying to diagnose, especially an amateur.

I haven't been involved in the long thread, but using a volt meter on 12v circuits often can give false info. Use something that can draw current, like an incandescent test light or the LOADpro test leads: https://www.esitest.com/P/142/180LOADproDynamicTestLeads

Also, physically tug on small wires.....and also, just toss a master disconnect solenoid (relay) and a starter relay at it. They are relatively cheap, and do fail intermittently. And guys that turned wrenches for a living know that come-backs are a big no-no. Sometimes ya just gotta shotgun it a little bit.

Jay you had me until the last sentence …. Never ever just replace parts because they are cheap and go bad often. Troubleshoot the issue and replace parts when the diagnosis supports replacing a part. The shotgun process will end up costing you more than the cheap part and you will likely still have a broken plane.

And this is where Dalton stands at this point.

I have worked with him in private and with the testing has pointed to a bad master contactor.
He has one on order and when it gets installed the wiring from the master switch will need to be traced out and confirmed.

I an not an A&P but have a very good understanding of basic electricity starting with 4 years in a tech High School and the next 47 years in industry.

Aside from all the legalities about Dalton needing an A&P if he could locate someone local who knows how to use a meter to troubleshoot that plus a phone call to someone familiar with planes might allow him to get his issue located and fixed.

Or find a traveling A&P and pay them to come out. My guess is at this point your going to need a flight permit to get to over for your annual. So you can take care of both at the same time.

Thanks for the input. It is great, in theory. I'm guessing you've never had to make a schedule or get equipment up and running in which the per minute down time cost 10x the price of the part?

Diagnosing and isolating the faulty component is key to solving the underlying problem. But intermittent issues don't always allow for solid data gathering. One has to use wisdom and experience to assign most likely causes. So if this was a plane that needed to fly, and was having intermittent start issues, and via testing and symptom analysis one has isolated the potential failed component to two relays, then someone that sees the big and small picture will throw two relays (solenoids) at it.

Failures are usually one single component, and it's always better to spend an extra hour or two troubleshooting and reviewing all technical manuals/diagrams/etc, but some times is crap or get off the pot.

I had a very similar issue with my Cessna 150M. I replaced a 6 year old battery, and in the process discovered that I also had an underlying issue with either my battery solenoid or Master solenoid.

My hangar neighbor is a very knowledgable electrician. He owns a Marine repair facility on the Mississippi River. So he was helping me. We spent 3 days trying to figure out how to rewire the Battery and Master Solenoids to the electrical system.

The OEM solenoids have 3 posts, the new replacements have 4 solenoids! Now Kurt is a wizard with an Amp/Ohm meter, but he was still having a difficult time getting everything figured out. And yes we were using the maintenance manual and wiring diagrams. We were going crazy trying to get it all sorted out. But we did.

And even though I am an A&P /IA, I know my limitations and know when to get expert help. Both for electrical and welding projects.

I have gotten a little bit into this story with Ron, as he called me for some additional information that he didn't know. So I am familiar with the back story of this problem.

When I taught systems at TWA, Kalitta Air and Flight Safety International, I can teach you the principals of an aircraft electrical system but don't ask me to help troubleshoot it too deep. I would tell my students that in the final analysis the simple answer to any electrical problem and it's solution is... PFM. Pure Fu@k!ng Magic...


I hope Dalton and Ron get this all sorted out.

Was the original 3post used the mount for the ground of side of the coil. And the new 4post was isolated and required the extra post to be connected to ground???? Cause that's pretty common....these solenoids are special for airplanes lol

I believe the original 3 post solenoid is internally connected to the 12 volt side of the solenoid and the master switch puts ground to the 3rd post.