Last weekend I swapped my engine because I couldn't afford to fix the one in the truck right now. The donor motor I put in had some parts that didn't match my '91 or '93 so I am assuming it is an older motor, I swapped some things over and everything seems fine.

The only issue I am having is that my oil pressure light is coming on. It as off at idle and comes on faint as I accelerate. The faster the engine revs the brighter the light gets.

At the end of my swap when I was hooking all the small wires back to the motor I noticed that the oil pressure sender was a different shape then on my other motor but it had the same plug so I hooked it up and thought nothing of it.

I was wondering If the light is doing this because this sender isn't getting along with my dash or should I be worried about the oil pressuse in my engine?

 

Could be all of the above!

It might be the sending unit it might be the oil pressure .

Do you have any history of this engine??

I say put a mechanical gauge on and see what happens and go from there.

 

The only thing I know about the engine is that it came out of a 4 Runner that was bought by a friend of mine from a scrap yard. He thinks it was an '89 but we are not sure. I don't know any details about the runner, but I wondered if it was an SR5 would it have a different sender for the oil pressure gauge as opposed to my base model which just has the light?

 

Was the original one very short (about 1" high)made for a socket to fit over it with a tab on the top?
If so that is an oil pressure switch closed with the key on engine not running and it opens once the engine starts and there is a set amount of oil pressure. These are made to work with an oil pressure light.
Is the one on the engine you put in bell shaped (about 2" high) with a tab on the top and on the bottom there is a square above the threads that takes a 14mm. wrench to install it?
If so that is an oil pressure sender. It is a variable resistor that allows current to flow to ground and the resistance changes with oil pressure. It is made to go with an oil pressure gauge (which you don't have). The reason your light is flickering after the engine starts is because this sender is allowing some current flow to ground.
Remove the sender and install the switch from your old engine and you will solve the problem.

 

That is exactly what I thought, thank you for confirming it.