4450 electrical gremlins.

Im working on this tractor for my boss. Everything worked fine this fall while it was on the grain cart and since that time it has pretty much just sat in the shed. The problem started when I was checking lights while doing the spring service. Had a flasher bulb out on the cab. Got pulled off on a different project so didnt get around to changing the bulb until the following day. At which point I lost all 4 flashers. So I started back tracking. Feed battery power directly to the left and right flasher harnesses lights work fine. Feed power directly to the flasher, flasher works fine except no turn signals. Go back the the main light switch and all sorts of weird things start happening. No flashers in the W position. Go to the H position. With dimmer in high I get inside set of front cab lights, no hood lights and no rear lights. With dimmer set in low I get outside front cab lights, hood lights and no rear lights. Go to F on switch. And its the same with no rear lights in any position. There are 3 wires going to the front cab lights, green, blue and yellow. Green goes to one light on each fender. Yellow and blue are tied together and go to the other light on each fender and it appears the blue wire also goes to the rear floor light on each fender. Dont know if this is correct but its for your reference so you know what Im looking at. Been banging my head against the wall on this thing for 8 hours and I need an outside viewpoint. So is this a light switch problem, or is it one of the lighting relays under the dash? Or suggestions?

Also for reference I believe this tractor has what is referred to as the investigator 2 dash.

I have seen several weird trailer light problems caused by faulty ground connections

It would be hilarious if you boss posted on this same topic under a handle of jockofbush, but that is exactly what happened. Or at least I will say someone posted on Tractor Talk wanting a 4450 wiring diagram but did not give a description of the problem they were wanting to fix. It just so happens that one of the examples of manuals I found for that post actually has a wiring diagram page folded out as an example and it covers the cab and lights. Go to my reply in the linked post and open the eBay manuals link. Then click on ..See full description.. then you can see the page. It shows a ground for the system about the middle of the page is on a stud of the engine oil filter mounting base. I would check that out and another one a bit to the left shown above the dome light switch. That one just may be a ground local to the switch as is shown on the diagram. Their are also individual local grounds by some of the lights. Hope this helps, some of the numbers along the wires and in the plugs are hard to read or at least expanding it on my phone they are.
JD 4450 wiring diagram post

I don't think the Investigator II monitor system is your problem. We are talking here about the operation of the control system for the lighting.
I believe your problem may be with grounds. Poor grounds may compromise the operation of the relays and may cause a back-feeding to ground through various electrical systems.
This can be a common problem with antique cars, tractors and up through fairly modern aircraft, and even our favorite, - the TESLA!
Things get messed up when there's corrosion and loose connections.
Get your multi-meter out and test for resistance or run a jumper wire to a known good ground on the battery or the frame of the tractor to the cab and observe the result.

Could have been him. He said he was going to try to get a diagram over the weekend. Dont know what his ag talk handle is though. Im confident the local grounds at the lights are good since this tractor has been converted to LEDs and usually if the ground at the light is even slightly flakey they just flat wont work. I guess Ill go to the main grounds and start from there.