Where is the oil pressure guage sending unit on an 89 sub?

[Canadianbuilder]

i bought a f.i. 89 sub minus the engine and trans.I swapped in a small block from an 88 extended cab.When I was doing the swap I noticed the sending unit at the back of the engine below the distributor didn`t match the plug on the sub wiring harness.I took the sending unit from a small block from a 89 crewcab I had and put it on the engine I put in the sub because it matched the wiring harness plug.I thought the extra wire in the plug was for my oil pressure guage.Unfortunately my guage isn`t working.The needle is always pegged to the right.I noticed the 88 engine has a sending unit at the back of the engine on the drivers side.Is this the actual oil pressure sending unit?If so I can`t find a corresponding wire with a spade terminal in the sub harness to connect to the sending unit.Am I just not seeing the wire?or is that sending unit for the guage in the 88 style trucks only?Thanks.

 

[4xcrazy]

There were a couple of different style of plugs, i found this out tryint to troubleshoot a problem awhile back, either a two or a three wire plug, need the right one for that setup. Not exactly sure what you have goin on though, kinda tired, and can't think too well at the moment

some others will pop in here in a few to give alittle more detail as to what i am trying to get at.

 

[Canadianbuilder]

Thanks 4xcrazy.Yeah the sub has a 3 wire plug and the donor engine had a 2 wire sending unit.I took a three wire sending unit off another engine I had from an 89 f.i crewcab and put it on the donor engine but the guage doesn`t work.Thought maybe there was another wire to go to the other sending unit the donor engine has.I guess the other sending unit is just for the 88 style trucks.I guess maybe the pressure guage might ****ed but I think I changed it.I can`t remember though been a year since I worked on it.Any chance the guage has a bad ground?If so anyone know where the ground for it is?Thanks

 

[dyeager535]

Three wire combines the oil pressure switch and the gauge sender from the previous single wire oil pressure sender/dual wire oil pressure switch.

You too can run it this way, I like it better, cleaner, less parts, etc.

A wiring manual of the correct year truck should indicate how they are wired, or you can go to Napa and look in their Echlin catalog at the senders, those too show wiring of the senders.