Re: How do you test a starter solenoid?
The true Case solenoid has four terminals on it. The two large diameter terminals are for the heavy lead coming from the battery and the heavy lead going to the starter motor no matter which engine is under the hood.
The two smaller terminals are connected as follows. One terminal receives a lead coming from the "Start" terminal on the ignition switch. The other terminal receives a black lead coming from the safety switches put on this tractor to save you from harm or to keep others who might try to run this tractor (like your kids or wife for instance) from being harmed.
IF...you have the correct four terminal solenoid, then test it by taking a length of wire with bare ends and grounding one side of the wire to the negative terminal on the battery and touching the other end to the small terminal on the solenoid that does not have the wire from the ignition switch going to it. If you turn the key to "Start", the engine should crank. If it does, then that is telling you that you have a safety switch issue that needs to be repaired, NOT BYPASSED. The usual culprit is the neutral safety switch that is found directly under the dashboard where the travel lever resides. There is also a safety switch on the lever that engages the mechanical PTO. Later tractors (Ingersoll's) also have a seat presence switch. The neutral safety switch itself might be OK but it gets grounded by the rod on the travel lever and if rust or corrosion is present, then grounding does not take place. I mean..... whadda ya expect after twenty plus years? LOL It could also be a broken wire on the safety switch circuit. It's not hard to trace these wires and find the true problem.
While you are at it, go test the one you took out but running a positive and negative lead from any 12 volt battery to the small terminals on that solenoid. If it clicks in, then coil in the solenoid is good but perhaps the copper washer and studs inside the solenoid are pitted so badly that they don't allow heavy current to flow from the battery to the starter every time you tried to start the tractor.