Solenoid questions

I have a 57 Ford 600 that I converted to 12 volt years ago and it has worked great for years. I ordered a solenoid from a tractor supply but it is a four terminal rather than the old three terminal. The old one worked with the push button start which is a ground button but that no longer activates this solenoid. I know that some solenoids have a grounded base and others don't. Using an ohm meter, I have full continuity between the base and S terminal and the needle only goes half way between the base and I terminal. Also the needle goes half way between the S and I terminals. I've been told I need to run a positive lead to the S terminal and not use the I terminal at all. Is this accurate? That would mean replacing the push button which has a single terminal with one with two terminals. Rather than experiment and short things out, I would like to know if this is correct. If I don't use the I terminal, how do I run power to the coil? It may be easier to just find a coil with only three terminals, but I have four old tractors all wired differently and would like to understand how both a grounded base and non-grounded base solenoid should be wired. Thanks for your help. Russ

Sounds like wrong type of solenoid. Some activate with ground applied to single small terminal (like yours should be) and others with power applied to small terminal (probably what your new one requires). Answer is not re-wiring or bypassing neutral safety start button, but rather to get the correct solenoid.

The 4 terminal solenoids I have used, one on a tractor and one on jeep, are activated by switch or push button hooked to one terminal and other terminal goes to coil to bypass resister for starting. Your new one seems to be set up differently. I don't believe on mine that either terminal has continuity to ground or there would be a short when starter button was hit.

Ford built millions of cars and trucks and tractors "back in the day" with the "ground the little solenoid terminal to make it start" setup.

NO need to re-invent the wheel and re-wire the tractor and lose the neutral start safety function when the correct solenoid is readily available from many sources.

On the other hand, if you have the correct 4-wire solenoid and wire it as shown, you can make it so that in addition to it having to be in neutral, ignition switch needs to be "ON" as well to enable cranking.

<img src = "http://www.gondtc.com/~blweltin/Bob/8N4-wire%20solenoid.jpg">

Save yourself some time. Get the correct solenoid. I see this all the time in the generator world.