Starter solenoid question.

[fluidpowerpro]

I have an MF85 tractor and last week I was using it to pull some logs. Out of the blue it quit starting. I would push the start push button and nothing would happen. The first thing I checked was the start solenoid so I pulled it and tested it on the bench. As suspected, I put 12v to the start terminal and it did nothing so it confirmed my suspicion. 
I picked up a new solenoid at an auto parts store that seemed to be a match as it looked exactly the same. 
I installed it in the tractor and no luck, still doesnt work. 
Ive been troubleshooting with a vom etc and nothing is making sense.
The weirdest thing is that the start terminal on the solenoid is now always hot.  I would think that if there is power at that terminal the solenoid would be engaged but it isnt.
I ohmed from the battery terminal on the solenoid to the start terminal and I have continuity so thats why its always hot.
One time I worked on an old Ford tractor that had a Ground Positive system. My tractor is not Ground Positive but I wonder if those systems use a different type of solenoid?
Maybe I got the wrong type of solenoid?

The system consists of a key switch, a push button switch that should engage the starter and a neutral switch thats on the transmission to insure its in Neutral before you can start.
Ive checked all of those with a VOM and as far as I can tell they are all functioning correctly. 

Any ideas as to whats going on?

Any help will be much appreciated.
Tom

[Magicman]

You could be reading 12vdc with your vom but still have a resistance (dirty) connection that will not allow the current draw (amps).  Also check that ground connection at both the battery & frame.  All of that is assuming that your battery doesn't have an internal problem.  You have a gremlin.

[Wlmedley]

FPP ,I've found over the years that a simple test light is all that is usually needed for most equipment troubleshooting. A Voltmeter doesn't pull any amps and will sometimes show voltage when there isn't enough to do anything. Over the years I used my test light a lot more than my voltmeter and found it made troubleshooting a lot easier. Sounds like you may have a ground problem.

[Wlmedley]

If start terminal on solenoid is hot and you have continually between big hot post and start terminal maybe start button provides a ground to ground terminal on solenoid to engage it . I can't recall ever seeing anything wired that way but it's possible.

[fluidpowerpro]

Thanks for the suggestions.

I worked on it some more and after pulling the new one back out I found that the base is stamped in tiny text 6V, so its the wrong voltage. The old 6v tractors were Ground Positive so I think that might be why it has the continuity between the 2 posts. Either way I'm not going to dwell on it at this point. 

I dug around and found an old start solenoid I had laying around from another machine. The posts arent positioned right to use permanently, but I figured it was good enough for a test.

I hooked it up and it works exactly as I would expect.

Now I just have to get another start solenoid. 

Live and learn. 

I told the guy at the store it was from a tractor and he asked 6v or 12v. I said 12 but still ended up with a 6 v.

I should have examined it closer before leaving the store.

The one I need is like a Standard SS581T except that one is 4 post. I'm not finding any 3 post versions on line so thinking maybe it going to be hard to get. 

In order to use the 4 post instead of 3, I think all I need to do is ground the extra post?

Wlmedley, actually yes, I also use a test light. Its one with a ground wire and clamp with a probe. 
I use it often as well as a VOM.

[newoodguy78]

FPP I believe you are correct regarding grounding the fourth post. Just went through that on my mill. Broke a terminal off the solenoid taking it apart to clean the connections. Happened to be a 3 post on there. They wanted $125 for a replacement. Dug around and had a new one in my electrical box that was a 4 post. Hooked it up and didn't do anything. Ran a ground to the fourth terminal and worked like a charm. 

[rusticretreater]

https://www.reliableaftermarketparts.com/products/els60-0087-12v-solenoid?srsltid=AfmBOoqjkDQTjLNIK81Dm0m_fLnYAsLEz2zK8cGSZdZXpFsj3s9lTvJz

[fluidpowerpro]

I got the tractor going today but it was bothering my why the first solenoid didnt work so I sat down and sketched up a circuit to see if it would support my theory that it was intended for a positive ground system.

I think my theory was correct because I was able to come up with a circuit that would work.

[arojay]

'Yestereday's Tractors' store might be worth a look.

[Wlmedley]

FPP, I'm the same way, I have to know why something works or doesn't work. Just getting it fixed isn't good enough. I could never stand to just be a parts changer. Your diagram makes sense  to me although I have never worked on anything that had a positive ground although I once worked on a rock truck where a fellow charged a set of dead batteries with his welder and the leads were reversed. Just about drove me nuts and cost a lot of money to repair.

[doc henderson]

I once was working on three-way switches.  bought a new one and the circuit still did not work.  I bought a bad 3 way.  they must have had a bad run cause I have got 3 bad ones from the store over the years.  I now know all about 3- and 4-way switches and circuits.  

[fluidpowerpro]

The only reason I was aware of positive ground being a thing was because I  worked on an old Ford 8N that was a 6v system. The positive terminal of the battery was wired to the frame at which point I go What????

[doc henderson]

old VWs were positive ground too.

[fluidpowerpro]

Was laying in bed this morning and for some reason realized that the circuit I showed yesterday was wrong. 

This one is correct.

(actually I was testing you guys    )

[fluidpowerpro]

.

[barbender]

Wlmedley, trying to troubleshooting something that someone has had their filthy hands on first is the worst. I'm working through some issues on a Detroit 4-53 right now, trying to figure out mistakes made by hands that didn't belong there. It's not fun at all.