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Air Con Confusion

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Good Afternoon All,

I've run into some confusion on the Air Con wiring on my Federal 1979 S2.  Specifically, I can't seem to figure out how to connect the Thermistor wiring to the wiring depicted on the Wiring Diagram.  The Thermistor has 5 wires that are supposed to terminate with the various wires indicated on the Wiring Diagram.  The (2) White/Black wires attached to the Thermistor and are designated to terminate with the White/Black wires on the wiring diagram (temp sensor) - no problem there.  Similarly, the single Black wire can assumed to be a Ground wire so I can easily connect that to the Ground junction - again, no problem.  The problem arises with the remaining (1) Red and (1) Green wires.  One of these wires needs to connect to the Yellow/Green wire that lands at the Fuse Box and the other has to connect with the (2) Pink wires that connect to the Fan Relay and the Air Con Compressor.  I've looked at the Thermistor wiring carefully and cannot determine how these wires interconnect with the wires as depicted on the Wiring Diagram.  If there were wires attached to the Pot I could logically assume they would attach to the Pink wires (that run to the Fan Relay and Compressor) as shown on the Wiring Diagram - no such luck !   I believe the wires attached to the Thermistor are original.  Can anyone provide some insight on this ?

Thank you,

Lou R


Thermistor 2.jpg

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Hi Lou,

The thermistor is in fact that probe which is located within the HVAC casing and adjacent to the evaporator cold side so as to translate cabin air temperature into an electrical resistance value. It has 2 wires colour matched to the 2 white/black terminating in that plastic plug shown in your pic. The LED feed speaks for itself, while the remaining 3 are uncertain as non-conforming to the wiring diagram from which I've been working. We know that a further 3 connections are needed: 1) A/C clutch activation (pink); 2) Ground or Earth (black); 3) +12v power (green/yellow), colours as published in the diagram. Will shortly examine my control unit to compare wires with yours.


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The 2 green wires are common therefore safe to conclude that the brass ended item should connect to the pink feed out to the A/C compressor clutch. The black (or is it B/W?) must be the earth connection so that leaves the red as connecting to the green/yellow +12v power feed from fuse block.

I'd not run the system without a relay for clutch activation, thus sparing the controller circuit from that load. Use the pink as control, wire a fused feed through the relay for A/C operation.


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Hi Steve,

Thanks for clearing that up.  Good advice on incorporating a relay into the wiring for the compressor.  The only problem I have is finding a location to place the relay and tapping into the fuse box for the relay power.  Sounds simple enough but I much prefer to avoid drilling any extra holes that weren't put there at the factory.  I've already added extra relays for the fans (which had an impact on the A/C wiring requiring an additional pink wire to the extra relays and an extra diode) and plan to add an additional 4 relays for the windows and 3 more (I think) for the headlights.  So far I've had to drill a number of non-factory holes to accommodate cooling fan relays and circuit breakers (in the boot for accessibility) and I'm certain that will increase as I look to complete the various other installations.  I'll look tomorrow and see if I can find a convenient location for the new compressor relay.   

Thanks again for your help.

Lou R

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