8070 idiot lights

On my 8070, I'm having problems with my idiot lights randomly going on and off without reason. I just got this tractor going this spring, so this is the first years that I'm using it. My engine oil pressure light has stayed on all of the time, despite a new sending unit. It has oil pressure (50 lbs. warmed up at 2400 RPM's). The voltage light really has a mind of it's own. It started out as being on when I would first start up the tractor, then go out and stay out after about 30 seconds. Then, the first time I used the air conditioner, it would come on when I turned on the AC, and go off when I shut the ac off. Now, it is staying on most of the time, but will go off from time to time for no reason at all. I have an amp gauge, and it shows a charge of usually 15 amps, more with the lights or ac turned on. Then one day the hydraulic filter light came on (every filter on the tractor is new). I had just started making a pass seeding, so I figured I'd finish the pass, then look into it. By the time I finished the pass, that light went out, but the transmission filter light came on during the next pass. Before I finished that pass, it went back out, but then came back on again later and stayed on. I pulled the wire off the filter head and grounded it out, and the light went out, so I figured I'd better look into the filter, even though it was a new filter. The filter had nothing in it that would plug it as far as I could see, but I still changed it and the transmission oil (which also looked perfectly clean). After changing the oil and filter, the light was out when I started up again, but came back on again shortly afterwards. I've ran it probably for about 10 hours now with the transmission filter light randomly coming on and going out, but mostly staying on, with no ill-effects, so I think I have a electronics issue. One time, I turned the ac on, and the transmission filter light went out, go figure. Any ideas where to start to remedy this problem? Sorry about being so long winded, and thanks in advance for any help, Darrel 

I WOULD SAY A POOR GROUND

   That really sounds like a ground problem!  Check all of the main cables for corrosion, replace them if needed.  Be sure to check under the cable insulation at the battery terminals, too.  Be sure that the ground connection to the tractor is clean and tight, with no rust/corrosion.