I need to know the size/thread of the access holes in the engine where the factory oil-pressure and water-temperature sending units screw in.

Engine is 1989 !st. Gen.

 

Water is 1/2" at the d-side rear of engine.. Oil I don't know, probly 1/2" or 1/8". You can get oil pressure from the top of the oil filter mount, there's a 1/8" plug. Water temp can be had from any of the 1/2" plugs in the cylinder head. I have mine plumbed right by the thermostat housing. P-side front of engine 1/2" plug.

 

Thanks for the information.

Does anyone know for sure what size the OEM oil-pressure sending unit thread is??

 

i beieve that it is 1/8th