Ford 950 with 3 post Solenoid

[RD Green]

Hi all,
I bought this 1957 Ford 950, that had jumpers to make it run, because the 12 volt upgrade was never completed.
I replaced the key switch, and a new safety natural start button, but it will not start by pushing the button.
I believe the 3 post solenoid is for a positive ground tractor as the one for the 6 volt setup, but now it is 12 volt negative ground.
The new key switch up to the junction block, is on; the solenoid has only 4 wires on 3 posts, one to the starter on the left, the small 3rd post goes to the push start button, the right one has the positive from the battery and a wire from the amp meter.
I can jump between the right post (battery) to the small 3rd post and it will start
There is no power to the small 3rd post to go the ground when the push start is pressed, this is why there must be two different types on a solenoid.
The ones I see on the internet do not state if it is for a negative ground setup.
What am I missing?

 

[Harry in Ky]

It's amazing how many solenoid stories there are. It's also interesting how many different solenoids there are. Some three post, some four post. Some self grounding, some insulated (isolated, in some descriptions). To utilize a grounding start switch you need a four post solenoid with an isolated coil circuit. Not one with studs marked S and I. That style is usually self grounded and requires switched power to one post (marked S) to energize. The right one will allow you to put power to one small post, connect the other to your new start switch, and complete the circuit by pushing the start switch down supplying the ground when the transmission is in neutral. The three post solenoid won't work with that switch concept.

 

[RD Green]

Thanks Harry in KY,
I'm going by what The Ford manual had, it shows a 3 post, like the old 6 volt system. I've seen three other Ford with a 3 post that are 12 volt, but there are no numbers showing on those solenoids.

 

[Harry in Ky]

I'm still saying the solenoid you're using won't work. Not saying the original from back in '57 wasn't a three post and that's what the tractor came with, just that I wouldn't expect to find one today.

 

[Jim.ME]

First, external looks don't mean much, what's inside counts. A solenoid will work for either positive or negative ground so that is not the problem. 12-volts will work a 6-volt solenoid and sometimes 6 volts will work a 12-volt solenoid, so 12 on 6 is not the problem. You say you can jump from the battery post to the small terminal, and it will start. That means that solenoid has a grounded base which needs power applied to it to energize its pull in coil. Regardless of looks, it is the wrong solenoid as Harry has posted.

To use the original start button, located down next to the shift lever, you need an insulated base solenoid. A 3 or 4 post one will work. Echlin ST56 and Standard Motor Products SS-587 are a couple that should have 3 posts, are insulated base, and internal power to the pull-in coil, the starter button wire hooked to the small terminal provides the ground for the pull-in coil when the button is pushed. Echlin ST542 and SMP SS-580 are two 4 post solenoids that are supposed to have insulated bases. On a 4-post solenoid you hook a jumper wire from the battery cable post of the solenoid to one of the two small terminals and the wire from the starter button to the other small terminal. For extra security from starting some run a wire from the ignition switch to provide power instead of the jumper from the battery post. That way if the key is off the starter won't crank if the starter button is pushed.

Solenoids seem to get mixed up at times at the stores. For both the 3 and 4 post solenoids, I recommend having the part store guy check with an ohmmeter, or other continuity tester, to see that the base is insulated from all the terminals. On a 3-wire solenoid the battery post (when installed the battery cable must be installed on the correct post) and the small post needs to have continuity between them. On a 4-terminal insulated base solenoid the two small terminals must have continuity between them, no continuity to either large post. If they check it, you leave knowing what you have if you take it and try it, many places won't accept returns on installed electric parts; they still own it if they do the test before you buy it.

 

[Destroked 450]

A 3 post solenoid will work and it doesn’t matter if the system is positive or negative ground
However the battery cable needs to be connected to the left side and the starter to the right
Swap the cables and it should crank over from the button

 

[RD Green]

First, external looks don't mean much, what's inside counts. A solenoid will work for either positive or negative ground so that is not the problem. 12-volts will work a 6-volt solenoid and sometimes 6 volts will work a 12-volt solenoid, so 12 on 6 is not the problem. You say you can jump from the battery post to the small terminal, and it will start. That means that solenoid has a grounded base which needs power applied to it to energize its pull in coil. Regardless of looks, it is the wrong solenoid as Harry has posted.

To use the original start button, located down next to the shift lever, you need an insulated base solenoid. A 3 or 4 post one will work. Echlin ST56 and Standard Motor Products SS-587 are a couple that should have 3 posts, are insulated base, and internal power to the pull-in coil, the starter button wire hooked to the small terminal provides the ground for the pull-in coil when the button is pushed. Echlin ST542 and SMP SS-580 are two 4 post solenoids that are supposed to have insulated bases. On a 4-post solenoid you hook a jumper wire from the battery cable post of the solenoid to one of the two small terminals and the wire from the starter button to the other small terminal. For extra security from starting some run a wire from the ignition switch to provide power instead of the jumper from the battery post. That way if the key is off the starter won't crank if the starter button is pushed.

Solenoids seem to get mixed up at times at the stores. For both the 3 and 4 post solenoids, I recommend having the part store guy check with an ohmmeter, or other continuity tester, to see that the base is insulated from all the terminals. On a 3-wire solenoid the battery post (when installed the battery cable must be installed on the correct post) and the small post needs to have continuity between them. On a 4-terminal insulated base solenoid the two small terminals must have continuity between them, no continuity to either large post. If they check it, you leave knowing what you have if you take it and try it, many places won't accept returns on installed electric parts; they still own it if they do the test before you buy it.

Jim.ME,
Thanks, I'll it out

 

[RD Green]

A 3 post solenoid will work and it doesn’t matter if the system is positive or negative ground
However the battery cable needs to be connected to the left side and the starter to the right
Swap the cables and it should crank over from the button

Destroked 450,
Thanks, I will try this first, at $40 a pop on wrong solenoids, since I have this one

 

[Sean in PA]

Your 950 originally had a 6 volt positive ground system with a 3 post solenoid. Switching it to 12 volt negative ground should not require any changes to the starter circuit, only the ignition and charging circuits.

 

[john in la]

The original solenoid has 3 post.
2 large and 1 small.
The small post is hooked internally to the large post on the right side.
So the battery MUST be hooked to the large post on the right side.
The original part number is NCA11450A
If you want to buy the part from this site just search that part number. It is $14.30
If you want to buy the part local Napa has it under part number ST53 for $29.99
If you go to any other parts store ask for part number S53. This is the BWD part number. Any parts store can then cross it in what ever brand they sell.

This is the original 6v positive ground part.
The part will not care that the tractor is now 12v negative ground.

 

[RD Green]

The original solenoid has 3 post.
2 large and 1 small.
The small post is hooked internally to the large post on the right side.
So the battery MUST be hooked to the large post on the right side.
The original part number is NCA11450A
If you want to buy the part from this site just search that part number. It is $14.30
If you want to buy the part local Napa has it under part number ST53 for $29.99
If you go to any other parts store ask for part number S53. This is the BWD part number. Any parts store can then cross it in what ever brand they sell.

This is the original 6v positive ground part.
The part will not care that the tractor is now 12v negative ground.

John In LA,
Thanks, then why doesn't mine work, if it doesn't matter if it is positive or negative grounded

 

[Btzj02]

John In LA,
Thanks, then why doesn't mine work, if it doesn't matter if it is positive or negative grounded

The problem with the 3 wire solenoids is that you never know how the small third post is internally connected to the larger posts. The small post must be internally connected to the large post that is connected to the battery. Unfortunately you cannot tell by looking at the solenoid or ordering the "correct" part number. Use an Ohm meter to check for continuity between the small post and the larger posts to determine the internal connection. In my limited experience swapping the large cables isn't always possible due to the length of cables and tight spaces. Except for my 8N I now use the Insulated four post solenoids exclusively because I don't have to worry about the internal connection and it is easier to picture in my mind the electrical flow.

 

[Jim.ME]

John In LA,
Thanks, then why doesn't mine work, if it doesn't matter if it is positive or negative grounded

It is possible it doesn't work for the reasons I gave you in post #5 and Destroked 450 gave you in post#6. John mentioned the need for the battery cable to be on the correct post to supply power internally to the pull-in coil, as Destroked posted. Left and right can be confusing, just try swapping the battery and starter cables on the large posts and see if it works. Or use an ohmmeter/continuity tester to test as I described.

You need a solenoid with the circuit as shown in this picture.

 

[john in la]

John In LA,
Thanks, then why doesn't mine work, if it doesn't matter if it is positive or negative grounded

I believe your solenoid does not work because you have the wrong solenoid.
Let me try to explain to you and to others that do not agree with me how I got to that conclusion.

The solenoid on these tractors have a solenoid that has the small post connected to the large battery post internally.
When you ground this small post (with the starter button on the trans) it makes the plunger move in the solenoid connecting the battery and starter cables.

They make a solenoid that looks the same externally and is more common on cars so this is the one a parts store will give you and are more likely to have in stock.
I do not have a picture of the 3 post solenoid I think you have so I will use a 4 post picture.
It is the same as yours it just does not have the 4th post that gets connected to the coil.
In this solenoid the small post is connected to ground and connecting power to this small post will make the engine crank.

So let me explain why I believe you have the wrong solenoid and why I believe others are sending you down the wrong path.
In your original post you said and I quote......
I can jump between the right post (battery) to the small 3rd post and it will start
This leads me to believe you have the wrong solenoid because that is how the wrong solenoid works.
Touching power to the small post to the wrong solenoid will make the engine crank because the small post is connected to ground internally.

So do you have a test light or volt meter.
If so lets do a test to prove me right or wrong before you buy another solenoid.
Hook the battery to a large post.
Try both sides to satisfy others here.
Now with a test light see if you have power to the small post.
I suspect you will not have power at this small post no matter where you hook the battery cable.

 

[Jim.ME]

I believe your solenoid does not work because you have the wrong solenoid.
Let me try to explain to you and to others that do not agree with me how I got to that conclusion.

The solenoid on these tractors have a solenoid that has the small post connected to the large battery post internally.
When you ground this small post (with the starter button on the trans) it makes the plunger move in the solenoid connecting the battery and starter cables.

View attachment 112975

They make a solenoid that looks the same externally and is more common on cars so this is the one a parts store will give you and are more likely to have in stock.
I do not have a picture of the 3 post solenoid I think you have so I will use a 4 post picture.
It is the same as yours it just does not have the 4th post that gets connected to the coil.
In this solenoid the small post is connected to ground and connecting power to this small post will make the engine crank.


View attachment 112976



So let me explain why I believe you have the wrong solenoid and why I believe others are sending you down the wrong path.
In your original post you said and I quote......
I can jump between the right post (battery) to the small 3rd post and it will start
This leads me to believe you have the wrong solenoid because that is how the wrong solenoid works.
Touching power to the small post to the wrong solenoid will make the engine crank because the small post is connected to ground internally.

So do you have a test light or volt meter.
If so lets do a test to prove me right or wrong before you buy another solenoid.
Hook the battery to a large post.
Try both sides to satisfy others here.
Now with a test light see if you have power to the small post.
I suspect you will not have power at this small post no matter where you hook the battery cable.

I may be misreading these posts, but I don't see that anyone has been sending him down the wrong path or disagreeing with you. You are telling him the same basic info I gave him back in post 5 and the circuit of the three-post solenoid insulated (aka isolated) base one he needs to use (with the original type of starter button is in post 13). What I see is that others have been telling him similar to this. Whether the solenoid has 3-or-4-posts, he needs an insulated (isolated) base solenoid to use the original type of starter button.

Is it possible a jumper from the battery cable hooked to the wrong post could energize the pull in coil if the other end of the pull-in coil is hooked internally to the post now going to the starter, where the starter would act as a ground? Admittedly I would expect it to drop out once the major contacts closed and passed battery current between the two large posts.

RD Green needs to do the testing that has been suggested and report back. Either swapping the battery and starter leads around or checking it with an ohmmeter or continuity tester, as has been suggested will solve the question of whether the solenoid he has is hooked up backwards or if he needs a different solenoid.

Here is a circuit picture of what I think he has for a solenoid currently and I think you are describing for a 3-post solenoid. If this is what he has it is wrong for use with the original type of starter button.



I believe we are all trying to head him to the same place.

 

[john in la]

I may be misreading these posts, but I don't see that anyone has been sending him down the wrong path or disagreeing with you. You are telling him the same basic info I gave him back in post 5 and the circuit of the three-post solenoid insulated (aka isolated) base one he needs to use (with the original type of starter button is in post 13). What I see is that others have been telling him similar to this. Whether the solenoid has 3-or-4-posts, he needs an insulated (isolated) base solenoid to use the original type of starter button.

Is it possible a jumper from the battery cable hooked to the wrong post could energize the pull in coil if the other end of the pull-in coil is hooked internally to the post now going to the starter, where the starter would act as a ground? Admittedly I would expect it to drop out once the major contacts closed and passed battery current between the two large posts.

RD Green needs to do the testing that has been suggested and report back. Either swapping the battery and starter leads around or checking it with an ohmmeter or continuity tester, as has been suggested will solve the question of whether the solenoid he has is hooked up backwards or if he needs a different solenoid.

Here is a circuit picture of what I think he has for a solenoid currently and I think you are describing for a 3-post solenoid. If this is what he has it is wrong for use with the original type of starter button.

View attachment 113009

I believe we are all trying to head him to the same place.

Sending him down the wrong path may be a bad choice of words but lets play this out.

He said if he hooks battery power to the small post the tractor will start.
This tells anyone that knows these solenoids that he most likely has the wrong solenoid because that is how the most common 3 post solenoid works. You apply power to the small post that is connected to ground internally and the motor starts.

Now lets look at what you and 450 are telling him.
Swap the battery wire for the starter wire.
So lets assume the battery and starter are on the wrong post.
Touching power to the small post of the wrong solenoid would do the same thing.
The tractor will start.
This is because the small post is grounded and touching power to it will connect the two large post sending power to the starter.
In this case he still has the wrong solenoid.

Now lets assume he has the correct solenoid.
If the starter and battery wire are hooked backwards.
Touching power to the small post will send power to the battery post because the small post and battery post are connected internally and on to the starter because he has the starter hooked on the battery post.
This will not activate the plunger in the solenoid but will fry the solenoid and let the smoke out because the windings in the solenoid are not big enough to support starter draw.
It will also make one heck of a spark as the starter tries to draw full starter draw through the small wire you are using as a jumper.

So I will stand by my statement.
If the original poster statement is true and the tractor started when he hooked power to the small post he has the wrong solenoid.
He can swap wires around all he wants and do whatever test you all want him to do but at the end of the day he still has the wrong solenoid because applying power to the small post with a jumper will not work if he had the correct solenoid no matter where he has the battery and starter wires hooked.

 

[Jim.ME]

Sending him down the wrong path may be a bad choice of words but lets play this out.

He said if he hooks battery power to the small post the tractor will start.
This tells anyone that knows these solenoids that he most likely has the wrong solenoid because that is how the most common 3 post solenoid works. You apply power to the small post that is connected to ground internally and the motor starts.

Now lets look at what you and 450 are telling him.
Swap the battery wire for the starter wire.
So lets assume the battery and starter are on the wrong post.
Touching power to the small post of the wrong solenoid would do the same thing.
The tractor will start.
This is because the small post is grounded and touching power to it will connect the two large post sending power to the starter.
In this case he still has the wrong solenoid.

Now lets assume he has the correct solenoid.
If the starter and battery wire are hooked backwards.
Touching power to the small post will send power to the battery post because the small post and battery post are connected internally and on to the starter because he has the starter hooked on the battery post.
This will not activate the plunger in the solenoid but will fry the solenoid and let the smoke out because the windings in the solenoid are not big enough to support starter draw.
It will also make one heck of a spark as the starter tries to draw full starter draw through the small wire you are using as a jumper.

So I will stand by my statement.
If the original poster statement is true and the tractor started when he hooked power to the small post he has the wrong solenoid.
He can swap wires around all he wants and do whatever test you all want him to do but at the end of the day he still has the wrong solenoid because applying power to the small post with a jumper will not work if he had the correct solenoid no matter where he has the battery and starter wires hooked.

We agree on the problem. In posts 2 and 4 Harry was trying to explain he had the wrong solenoid. In post 5 I posted " You say you can jump from the battery post to the small terminal, and it will start. That means that solenoid has a grounded base which needs power applied to it to energize its pull in coil. Regardless of looks, it is the wrong solenoid as Harry has posted." Isn't that the same as you are saying now?

Swapping the wires is a no cost thing he can try, if he wants. Do I think it will fix his problem, no I don't, I think he has the wrong solenoid as I said in post 5. But he can try that if he wants to prove or disprove the solenoid. He has the solenoid there, if it fries, he is not out anything, it doesn't work now. The testing with an ohmmeter I recommended (in post 5) he have the parts store do before accepting a solenoid, he can do on the solenoid he has, if he wants to prove which one he has.

So, I stand by my statement that no one is telling him wrong. In typical YT discussions, different methods are being suggested to get him to understand what is going on with the solenoid and that the solenoid he has is wrong. Some clear, some not so clear, and some unneeded (to those that understand to begin with).

Wording may be different, but we agree, he has the wrong solenoid. Now we just need to get him to test it somehow. Or get a known insulated base one installed. From a cross reference, I believe the Echlin ST56 is a 12-volt version of the 6-volt ST53 but given the lack of an internal schematic from Echlin or Standard on either one I would ask to have them checked in the store before leaving. And I think we all agree it would be helpful if the buyer's guides included schematics of each of these solenoid/relays, not just a few.

 

[JMOR]

Where there is a will, there is a way............. to even make the "wrong" one work

https://imgur.com/99b4uK0