The Snakes Alive CMP Wiring Project

[Jacques Reed]

Hi Mariano,

The direction of the magnetic field in a solenoid is determined by the current flow in it. if you swap the positive and negative terminals in a solenoid the direction of the magnetic field changes direction 180 degrees.

So, if a positive earthed solenoid (early Ford) was replaced with a negative earthed (later) one the magnetic field, and thus the force, on the armature, the centre part that closes the contacts between the battery and the starter, would be reversed.
This would cause the force on the armature to be away from the contacts and thus no closing of them to supply current to the starter would occur.

Search "Right hand Rule for Solenoids" for more info.

Also, as current flow by convention is positive to negative, perhaps "voltage activated" refers to a positive voltage applied to the solenoid in a negatively earthed one.

Hope this helps.

Cheers,

[m606paz]

Hi Jacques, thanks for your reply.
I say voltage activated according this diagram for Tractors

[Jacques Reed]

Hi Mariano,

I just put my multimeter on two old Ford starter solenoids. There was no continuity between the cases and the starter button terminals which indicates to me they are ground activated.

I also checked the continuity between the battery terminal (negative) on the solenoid and the starter button terminal and there was continuity there. This is the same at shown in the ground activated diagram.

There is no voltage at the start button. Only when it is pushed (earthed) does current flow from it, (positive) to the battery side of the solenoid, (negative)

Cheers,

[m606paz]

Hi Jaques
Thanks for the explanation, it has been very useful and a learning class for me.

So....
It's getting hard to get the right solenoid to work with the positive ground. All the ones I get here are postwar with negative ground.
Now, on the late electrical circuit data plate, it indicates that vehicles destined for India were negative grounded. What changes do I have to make to make it work with Negative Ground? Is it only to change the polarity of the battery and the instruments and electrical elements do not need changes? Only the solenoid is changed according to...?

Regards

[Mike K]

Originally Posted by m606paz

Hi Jaques
Thanks for the explanation, it has been very useful and a learning class for me.

So....
It's getting hard to get the right solenoid to work with the positive ground. All the ones I get here are postwar with negative ground.
Now, on the late electrical circuit data plate, it indicates that vehicles destined for India were negative grounded. What changes do I have to make to make it work with Negative Ground? Is it only to change the polarity of the battery and the instruments and electrical elements do not need changes? Only the solenoid is changed according to...?

Regards

Hi Mariano

The generator polarity needs to be changed if you are changing the battery terminals over.

The field coils in the generator are wound around iron cores, the cores have a small amount of residual magnetism in them that controls the polarity of the coils. It is easy to change the residual magnetism by quickly connecting a battery through the coils, it only takes a fraction of a second , the iron cores re-establish themselves with the opposite polarity .

[m606paz]

Thank you Mike for your valuable comment. I'll keep that in mind if I don't find the right solenoid.

[m606paz]

Before disassembling the harness, I leave photos and details of the part numbers of each switch