There are two temperature sensors, or more technically a temperature sensor and a temperature transmitter, near the front of the A Bank on the V12. One sends a signal to the temperature gauge, what does the other one do? And which is which?

On my car the transmitter is plugged in and the sensor isn't. I don't see a pair of wires anywhere for it. And the temperature gauge doesn't work.

Edit: It turns out that neither of these wires are connected. The transmitter wire runs forward, around the valve cover, under the AC pump, up into the V and terminates at an orange wirenut. It probably was connected to something at some point, but the exposed wire in the wirenut is quite corroded and no other exposed wires are visible in the area.

 

If I remeber rightly, the trail of both of those wires ends up in the loom on the B bank that also houses the wires from the ignition amps on the rad. I would bet that if you start opening the loom (it runs right up between and under the L shaped fuel tube and rubber off the fuel to the B bank FPR and the fuel rail and injectors - the coil wires and the dreaded shielded wire are all shared by and shoot out of this loom) you will find the terrminated leads to those sensor. Most likely by the PO or owners. The single is for the temp reading on the dash (I believe) and the other may signal the dummy light to turn on. Others will correct me if Im wrong...

 

The single wire sender is for the gauge, as mentioned

I think the other is the temp sensor for the Marelli ECU

Cheers
DD

 

Following up on this, the unconnected sensor is the Thermotime sensor, or at least that's the sensor that goes in that spot. They were only used on the early cars and some have them blanked off.

I did move the ac pump to trace the other wire. It turns out there are two running together in the bottom of the V. One goes to the temp sender and the other is goes to the wirenut. I did find a piece of wire with a connector at one end and twisted wires at the other, I think this had come out of the wirenut. I remember finding it when I moved the ac pump to change the sparkplugs, back in April. In the vaccinity there is another confusing wire. It comes from the back of the AC pump and has a connector crimped at the other end. There is a second wire crimped into the connector and this one grounds on a valve cover nut. Both of these loose connectors are the same gender, so maybe theres a missing plug somewhere or maybe someone used connectors in place of solder and heatshrink when joining wires? Any ideas?

 

Model year, Marelli or Lucas ignition, and wire colors would help narrow things down

The wire grounded to the came cover nut is some sort of previous owner thing

Cheers
DD

 

Its an ‘87 with Lucas ignition. I think the whole thing is a previous owner thing. I suspect that the wire in the V should connect to the back of the ac compressor, but I’m not sure.

 

Well, that broken connector in your pic looks like it could go to the compressor. You should see two terminals next to the compressor pulley. I'll assume (ha ha) the wires in question are A/C related.

An '87 could have wither of two possible wiring schemes.

The early design used a three prong "thermal limiter" fuse. You might see it near the compressor but it may have gone missing, thus the wiring quagmire to bypass it.
This system was wired as follows:

Green/brown wire from compressor relay to thermal fuse.
Green wire from thermal fuse to compressor clutch
Black wire from superheat switch (back of compressor) to thermal fuse
Black wire from connector at compressor clutch to ground


The late system was much easier:

Green brown wire from compressor relay to compressor clutch
Black (probably) wire from compressor clutch to pressure switch at back of compressor


Do you see a three prong thermal fuse or a solid green wire anywhere?



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Cheers
DD

 

How green is green? The wire in the picture that looks black is actually a black casing on a pale green wire. Is that the one or is it more of a darker green like the body paint (BRG)? I don't see a three prong terminal anywhere, although the car probably had one originally. It has a 8/86 build date. I do agree with you assessment that they are likely to be AC wires which is something that would be nice if it worked but isn't the top of my priority list at the moment. I may leave it as is for a while.

What is the top of my priority list is the coolant temperature gauge. It stays firmly on cold. I haven't gone on any long trips because of that, but 10 minutes of either idling or driving should have produced some movement I would have thought. I did change the transmitter today because that's easier that chasing wiring, but it didn't have any effect. So presumably I have a wiring fault. How strange to have that on an old British car. The wiring diagram shows two connectors between the transmitter and the gauge. One is presumably on the back of the gauge. Can anyone tell me where the other one is? Thanks!

Edit: the temperature gauge works just fine. I guess I hadn’t let it warm up enough after all. Went for a longer drive and came up to the bottom of the N and went higher. So back to the ac wiring...