Temperature sender/sensor & harness
 

Hi all.

I had a non function temp gauge from day one. I assumed the cluster had issues as most of the other gauges had issues also. However, going through the coolant system to start gathering parts for a one shot refresh of it, I found the temperature sender/sensor was in rough shape, had been e-taped and had some old rubber hose section around it for "insulation". So, this begs the question anyone know where to get a harness? Also, without pulling it how do I know which sender I actually have?

Re: Temperature sender/sensor & harness
 

Not really a harness. One Green SXL jacket wire from the sensor in the LH cylinder head to the bulkhead plug at the firewall.

If you decide you need some thermal protection you can buy thermal protective wire sleeve.

The sensor has a female Packard 56 terminal. Prior to 1981 the temp sensor could be one of the GM nailhead sensors or a 1/4" disconnect tang so the black plastic Packard 56 plug housing had a slot machined in it to slide over the nailhead or tang sensor connection or the 1/4" tang.
Here's a picture of an AC Delco 5665C repair pigtail with this connector. It's natural vinyl rather than the original black. You can look up the original Delphi Packard plug part number on the GM wiring diagrams.
Attachment 2180349

Nailhead sensor so you can see what I'm talking about...
Attachment 2180350

Re: Temperature sender/sensor & harness
 

Depending on year, the sensors have different temp/resistance curves. They are not one part number fits all.

Plus an idiot light sender looks much the same as a temp gauge sender and is often handed out by inattentive parts store clerks. The person then installs the wrong sender, notes that nothing changed(i.e. the gauge still doesn't work) and decides digging into the gauge cluster is more of a project then they wanted.

If you have an ohm meter you can test for a temp sender vs idiot light sender without pulling the sender. A gauge sender will have a resistance of from a few hundred ohms to a couple thousand while cold. An idiot light sender will show open. Of course a blown gauge sender might also show open so it isn't a definitive test. But if your sender shows an open and you have a gauge, you will need a replacement.

Re: Temperature sender/sensor & harness
 

The temp sender curves are inverted. Resistance is high with low temps.
Replacement aftermarket nailhead senders aren't the same resistance to temp curve as the originals.
Between 78 & 87 there are four or five different senders.
All of them will drive the gauge but the wrong sensor will drive the gauge needle to different locations than the original sensor.

Re: Temperature sender/sensor & harness
 

Attachment 2180380

Attachment 2180381

This is what I have going on. For some reason getting pictures to upload is being a real PITA.

Re: Temperature sender/sensor & harness
 

I saw a previous post you had answered on the same topic in 2018, but couldn't glean enough to self answer my question. As you can see my unit is like a Schrader valve inside.... Oh and it's an '84 Scottsdale 5.0

Re: Temperature sender/sensor & harness
 

Re: Temperature sender/sensor & harness
 

I dunno. It is wired straight out of the factory harness. Also, they do list a similar style with the plastic round body at the parts houses, again very Schrader looking so it could be factory. I should mention I have California emissions package electric carb, stock clutch fan.

Re: Temperature sender/sensor & harness
 

So what happens if I am getting a repop gauge from LMC? should I base the sender on it?

Re: Temperature sender/sensor & harness
 

The gauges in these rigs weren't high precision devices.
The replacement senders and likely the replacement gauges will differ from the original. Meaning the needle will not sit exactly where the OEM setup placed it at a given temperature. Whether or not it bothers you is personal preference.

I had three of these trucks and none of them had the temp needle at the same place when the engine was at full operating temp of roughly 185°F. They were kinda sorta in the same place but not exactly.
They tend to be a guide for what's happening. It's cold or warming up or normal or :ack:

Re: Temperature sender/sensor & harness
 

X2. I’ve always treated the factory gauges as a guide as a well. Non of them are super accurate.

Re: Temperature sender/sensor & harness
 

Okay, that info (and you pic) helps a lot. That appears to be the coolant temp sensor for the electronic control module that is used with the California emissions closed loop carburetor control system.

The factory wiring diagram for that system shows the connector for that coolant temps sensor as #12015008. Unfortunately, none of my web searches turned up anything based on that number so it's probably a part that has been discontinued / obsolete for a long time.

The sensor itself does appear to be available as # TX1 from Standard Motor Products. It is listed as fitting various GM (and a few American Motors) vehicles from the early 1980's. So you might get lucky and find a good used connector at a salvage yard.

By the way, this sensor has nothing to do with the gauge. That sensor should be located on the driver side cylinder head in the area between the #1 and #3 spark plugs.

Re: Temperature sender/sensor & harness
 

If you go this route, ask LMC which sender they sell that matches their gauge and go with that one. This way, if it reads way off, LMC can't blame "the other vendor's sender".