I put it on the lift, I think your both mistaken.. Unless you have 85s because the plug for the sender is right next to that port..
Here is the oil filter area,
If you look you can see the plug hanging there up by the block. So my thoughts are that someone had a bad sender and couldn't find one so they plugged it.. That's the only explanation I can come up with.
I checked the drivetrain pretty good because I have a gnarly growl from the middle to rear of the truck and kinda sounded like a bad rear end, it has to be the tcase it has a get distinct grumbly bearing sound almost like a bad throw out bearing.
I think this truck had a very very hard life, there is a lot of bent things.. Bent Trans x member, bend floor pan?? I don't even know how that happened.
There's about a mile of backlash in the front axle and half a mile in the rear, both are open diffs. In 4x the case doesn't have any backlash between the outputs so the chain doesn't see stretched, the front output moves a little and the yoke is toast, the rear isn't bad, I think if I put new u joints in it will make it new again.

Bent oil pan I think I showed early on.
Anyone know if an np241 is a bolt in affair? From my reading I need a 32 spline which would be in 88-91 trucks with a th400 or 465, if I am going to swap id like that extra reduction.