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Discussion Starter #1
A new 3 post starting solenoid should be internally hot, I've read that part dozens of times.

IF my local napa is clueless (don't ask....), can I test it with a continuity or OHM meter from the + large post to the little post, it should have continuity, right?

KRS
 

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Here's a drawing of a simplified starter solenoid that Kbeitz posted.



The little post is basically a circuit of its own (induces a magnetic field). It is not connected to the main bus terminals. When +12 volt DC voltage is applied to the small terminal stud the solenoid pulls (Pushes the plunger in the image) the large contacts together allowing higher battery amperage to flow from battery side to starter side of the solenoid.

You can bench test continuity on the coil by grounding the black test lead of your multimeter on the solenoid's metal frame and then the red test lead to the small terminal, you should get continuity there through the coil.

Another test is tape your test leads to the large terminal studs and check for continuity between the large studs/contacts. Put the solenoid metal frame to the negative post of your battery and then use a jumper wire to apply positive 12V DC power from the Battery's positive post to the small terminal stud. This will pull in the solenoids contacts and you will have continuity across the two main terminals, if not then it's a bad solenoid.

If the solenoid works correctly in the above tests then start looking for loose or damaged wiring from the ignition switch on the tractor.

Make sure all of your tractors ground wires are clean (on bare shiney metal) and tight! Also if the new starter solenoid has a blade connector on the side of the housing you will need to run a ground wire from it to the tractor's chassis.

Hopefully, I've explained it clearly enough to be of some help!

May want to post pics of your new and old solenoids.

:trink39:
 

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Discussion Starter #3
That picture and explanation makes sense.

Except, it doesn't apply to our tractors, right?

An 8n 3 post solenoid (based on my limited understanding):

1) Battery to large + post
2) Starter on large - post
3) Push button for starter engagement on small post

The push button (when depressed) grounds out the solenoid thereby sending voltage through the solenoid, out the - post, to the starter, right?

So, the large + post and the little post must be connected and "hot" together, otherwise depressing the push start button wouldn't do anything.

Also, the solenoid cannot be grounded internally to the frame of the solenoid (and thereby to the frame of the tractor). It must be isolated, right?

Let me tell you where I'm coming from: 8n I bought has a goofy wiring job, with a 4 post solenoid. I'm going to rewire, but I want to buy a local NAPA solenoid. However, I know there are differences so I want to get the right one the first time, so I thought I'd check it. And before you say "They'll know down at NAPA what you need", farming is gone from here and they won't know anything about tractors.

ps-> keep you head down over there, I've got a good number of buddies over there too :fing32:

KRS
 

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KRS,

Need to know if your 8N has been modified to a 12 volt chargeing system (negative chasis ground with alternator) or left original 6 volt (positive chasis ground with generator). There's different wiring for each system.
 

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Discussion Starter #5
Very true! 12 volt negative ground, alternator, and 12 volt coil.
 

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KRS:

That picture and explanation makes sense.

Except, it doesn't apply to our tractors, right? The image (above post) is the same principle for our tractors or for a lawn mower, just have to be sure that it is the correct style for the wiring harness and sized correctly for the amperage draw across the solenoids contacts. It's best to go OEM whenever possible but with older machines sometimes that part is out of production and a substitue part with the same capability has to be used.

An 8n 3 post solenoid (based on my limited understanding):

1) Battery to large + post {correct}
2) Starter on large - post {12V + is passed through the large stud contacts when the solenoids coil is energized by the key switch/ start button.}
3) Push button for starter engagement on small post {correct}

The push button (when depressed) grounds out the solenoid thereby sending voltage through the solenoid, out the - post, to the starter, right? {Correct ~ When the starter button is pressed in it makes the contacts touch allowing 12+ volts to pass through starter button energizing the starter solenoid coil making those contacts engage there by passing higher amperage 12V+ to starter making it spin.}

So, the large + post and the little post must be connected and "hot" together, otherwise depressing the push start button wouldn't do anything. {Incorrect ~ The large 12V+ lead on solenoid is always HOT on the battery side of the solenoid. When the key switch is ON and the start button is depressed then the solenoid's small stud will have 12V+ at that time to energize the solenoid's coil moving the main contacts together allowing current to pass through the contacts, spinning the starter.}

Also, the solenoid cannot be grounded internally to the frame of the solenoid (and thereby to the frame of the tractor). It must be isolated, right? {Depends on the type of solenoid ~ some manufaturers make their coils with an extra blade connection ( or 4 studs ~ 2 large and 2 small studs)
to plug a grounding wire from the small stud / blade terminal to the chassis (Neg.[-] ground) of the tractor while other coils use the metal housing / metal mounting bracket of the solenoid itself that mounts to the tractors chassis as the grounding point for the coil (main reason u need to make sure the solenoid mounting point has bare shiney metal as a good ground, this metal can be protected by dielectric grease to keep it from rusting, needs more grease applied if power washed!!). As you mentioned, the main leads from the pos. [+] side of the battery through starter solenoid and then to the starter can not touch the tractor's chassis since that is the negative side of the battery and arcing/melting will occur (at times very expensive when that happens)!}

Let me tell you where I'm coming from: 8n I bought has a goofy wiring job, with a 4 post solenoid (2 main 12V+ large studs and 2 smaller coil studs (one 12V+ and the other a ground [-] wire to chassis). I'm going to rewire, but I want to buy a local NAPA solenoid. However, I know there are differences so I want to get the right one the first time, so I thought I'd check it. And before you say "They'll know down at NAPA what you need", farming is gone from here and they won't know anything about tractors.

ps-> keep you head down over there, I've got a good number of buddies over there too :fing32: {Thanks!! I try to keep ALL of my body parts out of harms way!!:fing32:}

KRS



Hope this make sense to you!! :thThumbsU


:trink39:
 
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