I Have a 1987 GMC 1500, TBI, 305 cu in. My Oil pressure gauge is pinned all the way to the right, I tried changing the gauge and the oil pressure sending unit but it is still pinned to the right even with engine not running and key on. Any suggestions on what to try next?

Check the wires. There'* no signal getting to the gauge.

Is it a direct wire to the gauge? just in case i have to rewire

I believe it is, but I can't say for sure. But if you have to rewire it, I suggest buying a new mechanical gauge. Much more accurate.