Well, My dad bought a 95 K3500 1 ton dump with 106K miles, bone stock. The guage in the dash wasn't moving after warming up, so the logical (to me) first step is to get a sending unit. After I drained the system and pulled the radiator to pressure wash it (thanks guys for the tip on cleaning it) - BTW it took several doses of greased lightning and 2 cycles at the car wash, but its WAAAAYYY cleaner now! Anyhow, the stock wire harness has only ONE wire going to the unit. Problem is the new sending unit is set up for TWO wires. Now the fun begins. I went to NAPA and they sold me a wiring adapter (PN# TSC200) to go to the new sensor. This adapter also has two wires, one yellow and one black. My plan is change thermostat while coolant is out, install new sensor, and then warm it up and twist together one wire at a time to see which one works. (no instructions in the box) but if I go with the same side, it will be the yellow wire. Sorry guys, I don't have a digital camera, so I'll have to write how things turn out. Eventually I'll get one so I'll save the pieces for pics later. Got to go get dirty.

Scott

Correct me if I'm mistaken but aren't there two sensors, one with two wires for the PCM and a single wire unit for the gauge.

Yep . For a 97 at least. I just went out & checked.

I posted this in the part point sticky last year.

1994 6.5 F code
ECT sensor for PCM GM#15326386, ACDelco#213-928 (goes in the t-stat crossover)
CTS sensor for Temp Gauge GM#25037332, ACDelco#213-77 (goes in the drivers side head)

Ok, I'll be honest, I dont know if there are two or one, but on this 95, I'm aware of only the one on the drivers-side of the head, in front of the injector. I grounded the black wire and connected the yellow to the factory green wire. It acted like any other temp gauge, except that it didn't stop at 195 or 210 or 230, so I shut it off. The odd thing is the resivior was only warm (could stick my finger in coolant and no burning). No leaks at least.

The sending unit or coolant temperature sensor is a Wells unit pn # : SU109
NAPA stat pn # : 212

Whats that other stuff?

Scott

The sensor in the head should only have one wire, usually green (I think) and it's for the gauge. The sensor in the t-stat should have 2, black and yellow and it's for the puter. It sets glow duration accordin' to coolant temps. Take another look, you should have both.

Side note, I pulled the vacuum line off at the turbo, and used one of those fancy 4" dia vacuum gauges and from idle to rev - no reading, no vacuum.

Yeah, there's two of em (CTS's). Me thinks its time to visit the dealer - tomorrow, before I mess up any more.

Scott

Follow the vacuum line back to drivers side to the wastegate solenoid check for vacuum on the other side (vacuum pump side should be ~26").

Corolla, I went back to the pinkish line (the other side of solenoid) and it measured 24" at idle. The truck in my sig line has the Heath TM and no vac pump, so I'm gonna try to pull it off (solenoid) and swap it out to see if I get anything at turbo

Thanks guys for all the help

Scott

Corolla, it worked!! I've got 24" at turbo now. However, still nothing good to say bout the CTS in head. Coolant still cool at resivior and warm to touch at upper radiator hose. When I disconnected the black wire (ground) the gauge bottoms out, when I re-hook it up, its almost in the red. Guess I need to get the correct part from dealer after all...

Thanks again Scott

Corolla, it worked!! I've got 24" at turbo now. However, still nothing good to say bout the CTS in head. Coolant still cool at resivior and warm to touch at upper radiator hose. When I disconnected the black wire (ground) the gauge bottoms out, when I re-hook it up, its almost in the red. Guess I need to get the correct part from dealer after all...

Thanks again Scott

With ~24 at the vac pump you should have ~15 at the Waste gate or the modulating solenoid - in not modulating!! Give the solenoid a short of air tool oil and see if that wakes it up from its nap - its stuck full open.

OK guys, I have since replaced the wastegate solenoid with a new one and I get +/- 14" at gate. However, now I'm getting an occasional SES or SEL lite. I pulled the code and its a 78. I'm thinking about just pulling off the TM from the 94 and being done with it. (also thinking bout the marine inj's and the SS air filter while I'm at it) What would giving a shot of air tool oil to the solenoid do? Nap?

Oh yeah, BTW I finally got the right sending unit from the dealer, now to find the time to put it in.