There are a few different temps sensors it seems for the 12Vs.
I had a threaded one prong sensor on my '90 12V that I just put in my crew.
It was the only gauge that didn't work.
I grounded the end of the wire clip on the wire harness, and my gauge works, so the gauge is good.
I couldn't find the same style "threaded rod" ended, one wire plug in sensor so, I used a later style with the grey almost rectangular plastic wire clip on style and changed my wire end on the harness to use it.
My temp gauge still does not work.
My question is is do they work differentially, or Did I install another bad sensor.
The parts store lists three different temp sensors.
Thanks!

 

I found another threaded post design temp. sensor on a spare early '89 12V I have.
All my other '92-97 Cummins motors in my shop have the grey plastic clip on style.
I might try the other '89 temp sensor and swap back the wire pigtail, and see if gets my gauge to work..

 

what wiring harness are you useing ?all the first gen's I believe are the same thing ?

 

 

I am using my original '85 crew wiring on the '90 12V.
It was so easy to do it that way.
I just changed the oil pressure sensor on the block, and wired the hot key on, old coil wire to the FSS.
The speedo runs of the T-case, and the fuel gauge works as it should.
I never wired up my grid heaters as I only drive it in the spring and summer
I have noticed the early '89 and '90 12Vs use a different style temp sensor that has a different style wire plug in.
Otherwise the sensors looks the same and thread in the same spot in the block.
I am just not sure if the different temp sensors operate differently...or I just have installed the "newer" style sensor and it is bad.