What determines a 1 or 3 pin oil pressure sensor?

[Schurkey]

If I recall correctly, I do have something down by the oil filter adapter... or would that be a knock sensor? I do have a knock sensor by the starter.

If your '99 is like my '97, you'll have a knock sensor on both sides of the block. Unlike the small-blocks, the knock sensors don't thread into the cooling system block drain holes. They're in blind-thread bosses.

Fairly sure my '97 K2500 does not have an oil pressure sending unit or switch by the oil filter.

 

[454cid]

If your '99 is like my '97, you'll have a knock sensor on both sides of the block. Unlike the small-blocks, the knock sensors don't thread into the cooling system block drain holes. They're in blind-thread bosses.

Fairly sure my '97 K2500 does not have an oil pressure sending unit or switch by the oil filter.

Thanks for adding that information, on the knock sensors, Shurkey. I will take a look near my oil filter to see what I can see in case my 99 is different, as I know there are a few differences over the life of the L29.