New Holland TC45D saga

Please bear with me ...I have checked all the safety switches and replaced many; & battery is fully charged. Slow progress with more and more things beginning to at least light up properly. It started with simply no power at all...,I have read many threads on web concerning all loose cable underneath , pto safety switch , seat switch etc. I switch out ignition switch with 5 prong switch come to find out ...4 wires....finally bit the bullet and bought 4 prong switch. Now I get everything working on dash as it should plus a loud clicking sound? Is this the starter?why I ask..I replaced it about 2 months ago. My life would be easier if it was a bad starter.... I know how to do it!!
But I also read bad alternator click. Any and all guidance is welcome. I am retired and was unfortunately in an office environment so I learn by trial & error and have very little mechanical experience...but I'm persistent to solve this saga and use my tractor again.thanks in advance!!

That it is clicking is actually a plus. Since it is a loud click, it should be relatively easy to track the sound.

You say you have been checking switches, battery, etc. I assume you have a volt meter or test light.

Go to the starter, have an assistant hold the switch to start. If there is voltage between the cable lug or solenoid lug that goes directly into the starter case, and the bare metal of the starter case, and the starter is not turning, there is a starter problem.

If no power there, start tracking back toward the battery, see where the power stops. Do all the testing under load, as in while holding the switch to start, seated on the tractor, all safetys made.

Be aware though, it could decide to crank any time during the test!

I will add one thing to Steve's advice. If you have lights working, turn them on, watch them, and hit the start position. If they dim down, stop the test, things will burn up. If they stay bright and the click is coming from the starter solenoid, it is either the solenoid not making contact to the starter, or the starter is not functioning (electrically "Open" nit shorted). This assumes a good charged battery. Jim

Welcome to YT
Clicking sound could be a relay not the starter solenoid. Did you clean/tighten all FOUR battery cable connections? I suggest for you to acquire and study the NH tech manual for TC45D

This may have no bearing on what you're doing. It's my experience. I have a NH TT60A I bought slightly used, to (for shame!) replace one of my antique tractors! Unfortunately they have taken an old, simple, reliable Fiat design and added a bunch of modern electronics. I did buy the expensive repair manual. I was annoyed that it beeped at me if I didn't lock the brakes. I found the beeper up at the right rear top area of the engine, barely accessible under the hood, (as the hood hinges at the rear/lifts up from the front.) I was able to remove the beeper without compromising anything else. As I recall, there were three units there. The major benefit of this project was finding a loose wire in one of the units, as I was playing with things, trying to figure it out. You see, I had a starting problem. Occasionally, it would crank forever, but not fire. I had done everything I could to check out the injector pump/fuel system. The problem was, getting 12V to the pump. Turns out there was a loose wire end- one of those that's supposed to be locked in an insulator end, and plugged into this module. You couldn't see it. Apparently it was just kind of hanging there such that it would usually make contact, but then sometimes not.