1995 Peterbilt 379,coolant sensors

Does it possibly have a third sensor in front of the housing hid behind the alternator bracket? Could some wires be plugged up to the wrong sensor?

 

Should be a 3 wire sensor in thermostat housing down low pointing towards fan behind alt bracket. Did you change that. ?

Also might be 2 more . 1 high temp light in head . 1 for OEM gauge in top of thermostat housing.

 

One in the front of the thermostat housing is for the cat ecm. It sounds like the scangauge is correct so that sensor should be fine.
One on top is for the guage, the other one is for the warning light.
Make sure the wires are tight on the back of the guage, give them a wiggle to see if the gauge jumps.
Wiring is most likely bad between sensor and firewall. You could get a helper to look at the gauge and shake the wiring to see if it jumps.
Schematics should be pinned to the top of the pete forum.

 

I have a 94 with a e-model and it’s like swann posted. The 3 wire feeds ecm, one on top for gauge, one left rear corner of head.
Good chance the one for the gauge was hanging on by a thread.

 

We have a 1989 379 here that has a Cat crate engine in it. It has a single terminal threaded stud sensor and a two wire plug in sensor on top. The temp gauge works. When the left over wire is grounded the temperature light comes on.
The fitting in the lower front of the housing is a #8 male boss- o ring. When we order a sensor from Pete it is 1/2" male pipe, 215 N/O.
Cat points at Pete and Pete points at cat.
Does anyone know what sensor would work in this application?

 

What model of cat is it? Usually the cat factory 2 wire deutsch connector water temp sensor goes in the front. It is orb.
Then the unused hole in the top is 1/2 pipe and will take the warning light sensor.
I think the 2 wire sensor is wrong, is it being used?

 

1989 cat would be a 4mg 425 mechanical. The single wire is your high temp light. The 2 wire is just a normal kysor temp switch that turns the fan on. Should be OEM Pete.

 

3406E 550 HP The numbers are hand scribed on a Cat data plate. We have no history on the truck.
It has a plug in connector ( rectangular ) that I should recount the number of terminals on.
Next to it on top is another single stud push on connector. The free wire is a single push on connector When grounded it lights the high temp light.