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Discussion Starter #1
Two issues I have ran into on my 91 Diablo.

1 - All of a sudden both rear fans have stopped running. I have checked the fuses in the engine compartment box and not even getting power to the fuses. Relays back there appear fine but have not tested them yet. Strange for both fans to stop working at the same time.

2 - The reverse lights are not working. Never have since I got the car. Ran it down to the switch on the shifter. When in reverse, I am getting continuity thru the switch. But with the wires connected, nothing goes thru the switch. I took it out and connected it to 12 volts. When I push in the plunger,12 volts go out. But you put the slightest load on it and nothing comes thru. I connected the wires that go to the switch together and the reverse lights do light up. Total current draw is 3 amps. But cannot get a three amp load to go thru the switch. Very strange.... I guess I need a switch??

Thanks in advance...
 

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Waiting on this to go live, I have been searching the forums. From what I have read, the fans do not necessarily come on when the key is turned...Correct?? What mine were doing, and I thought this was normal, they would turn on to what sounded like full blast as soon as the key was turned, no matter if the car was cold or warmed up.
 

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Hi, Yes, fans do not come on with ignition;
Test this by fan switch terminals together, then you will know what part is wrong.

Have you check you got correct reverse ligth terminals? Rear fog light terminal is similar. Same thing with reverse light switch, I belive it grounds (not sure) , so wires together you know.

Both fan switch and reverse light go through rear fusebox, so check fuses for +12v feed, they might be same for both.
 

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In addition to what Mikael82 said, the fans are supposed to come on when the thermal switch hits a temperature rating high enough, I think it’s 80 Celsius, then go off when the coolant temperature hits 74 I believe. If they both went out simultaneously I’m wondering if your thermoswitch has gone bad. At least on my car it is on the left side of one of the U-shaped coolant pipes as you look forward into the engine from the rear grill.

As for the reverse lights,I suspect that you have a bad ground or a partially corroded connector on or near the light itself. That area is subject to some moisture and corrosion over time. However what Michael said regarding the fog light is interesting because in the US our fog lights on the rear do not work. The wiring harness however is still there and includes a European fog light connector. Could it be as simple as a prior owner had the reverse lights plugged in to the wrong connector?!
 

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Discussion Starter #5
I will do some more testing by driving the car when rain stops here to see if the fans come on after warm-up. I was afraid of driving it yesterday because the fans did not immediately come on when I turned the key and thought it might overheat. Like I said, since I have had the car, only a few months, the fans would turn on with ignition in either 1 or 2 position. Thought that was normal. So normal is for both fans to come on together when temp hits 80° C.... correct? and they are controlled by a thermoswitch on the coolant pipe on the left side of the car. And they are single speed fans, either on or off, correct? And any ideas why they would come on before with the key and now do not. Controlled by the same thermoswitch? @mikael82 are you talking about fan switch terminals on the thermoswitch @DiabloClyde is talking about?

As for reverse lights, there are two wires that connect to a switch on the shifter under the car. One is 12v all the time. When I go into reverse, it activates the switch and allows 12v thru it. But any load on it and the 12v disappears thru the switch. I can connect the two wires together and the reverse lights come on AND the auto seatbelt thingie moves rearward. Total amp draw is 3 amps. So my guess is the switch. Just never seen one act like that before, that is having continuity and losing it with load.

This car is a learning experience...... to say the least.
 

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I will do some more testing by driving the car when rain stops here to see if the fans come on after warm-up. I was afraid of driving it yesterday because the fans did not immediately come on when I turned the key and thought it might overheat. Like I said, since I have had the car, only a few months, the fans would turn on with ignition in either 1 or 2 position. Thought that was normal. So normal is for both fans to come on together when temp hits 80° C.... correct? and they are controlled by a thermoswitch on the coolant pipe on the left side of the car. And they are single speed fans, either on or off, correct? And any ideas why they would come on before with the key and now do not. Controlled by the same thermoswitch? @mikael82 are you talking about fan switch terminals on the thermoswitch @DiabloClyde is talking about?

As for reverse lights, there are two wires that connect to a switch on the shifter under the car. One is 12v all the time. When I go into reverse, it activates the switch and allows 12v thru it. But any load on it and the 12v disappears thru the switch. I can connect the two wires together and the reverse lights come on AND the auto seatbelt thingie moves rearward. Total amp draw is 3 amps. So my guess is the switch. Just never seen one act like that before, that is having continuity and losing it with load.

This car is a learning experience...... to say the least.
In addition to DiabloClyde and Mikael82, if the Climate Control unit window defrost button is depressed, the fan will turn On immediately.
IMG_2276.png
 

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Ray, we are talking about the coolant fans at the rear dual radiators on each side of the car.

Old South, yes, they only turn on above a certain degree and turn off when they hit a certain degree, again I believe it’s 80 Celsius on and 74 Celsius off. They are not supposed to turn on when you turn the key on. That confuses me: that maybe a prior owner wired the fans around the thermsensor switch. Maybe his wiring job has now failed? Another thing to check on your car on the left side or driver side in the US just forward of the rear tire and to the outbound side of the battery some people wire a fan on the oil cooler radiator. Could it be that an aftermarket oil cooler fan is the fan that you no longer hear? If you took off the tire then wheel well liner in that location you would immediately see if your car has one.

Also, you can start the car in the driveway and the temp would get high enough for the fans to turn on, so you don’t necessarily need to drive the car to test the fans. When you do, watch your water temp gauge to ensure it’s working. I would shut it down if you go past 100 C and the fans don’t kick on.
 

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Discussion Starter #8
DiabloClyde, removed the wing for access to the thermsensor. Connected the wires and both fans came on. Cranked the car and fans turned on between 80-100 then turned back off around 80 or so. So I guess everything is working properly. What confuses me is that they were on constant before. And it was definitely the rear fans... Maybe the thermsensor was stuck or something. I will keep an eye on it and replace the thermsensor if it acts erratically again. Thanks for all the info. You can learn a lot from folks that have been there before.
 

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Ray, we are talking about the coolant fans at the rear dual radiators on each side of the car.

Old South, yes, they only turn on above a certain degree and turn off when they hit a certain degree, again I believe it’s 80 Celsius on and 74 Celsius off. They are not supposed to turn on when you turn the key on. That confuses me: that maybe a prior owner wired the fans around the thermsensor switch. Maybe his wiring job has now failed? Another thing to check on your car on the left side or driver side in the US just forward of the rear tire and to the outbound side of the battery some people wire a fan on the oil cooler radiator. Could it be that an aftermarket oil cooler fan is the fan that you no longer hear? If you took off the tire then wheel well liner in that location you would immediately see if your car has one.

Also, you can start the car in the driveway and the temp would get high enough for the fans to turn on, so you don’t necessarily need to drive the car to test the fans. When you do, watch your water temp gauge to ensure it’s working. I would shut it down if you go past 100 C and the fans don’t kick on.
I stand corrected. The car needs to be running vs turning the key to on position. My bad
 

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Discussion Starter #11
They were connected to the sensor you told me about. I changed nothing. That leads me to believe the sensor was malfunctioning, but is now operating properly. Indeedly strange!
 

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Discussion Starter #12
When I said I connected the wires, I meant I shorted across them and the fans came on.... as a test.
 

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Awesome. Sounds like your sensor is the problem and should be replaced. At the end of the day these are fairly straightforward cars to operate and diagnose. Kind of fun to do so! good luck.
 

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FWIW, On my early US spec 91, One rear light (Left if i recall correctly) is for reverse and one rear light (Right hand side) comes on with the fog light switch.
 

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Discussion Starter #16
Arancio, that may be how mine is also. Just tried the rear fog and nothing comes on. Just like the backup light.

LOL.... now both fans come on when engine is cold and key turned to any position. I definately need the tempsensor!
 

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Keep in mind, iirc the headlights need to be on for the foglight to work.
 

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Old South, the sensor you need is here:
It's $189 on Bullstuff but you can check a variety of others including AMH and Eurospares.

Arancio, I can't wait to check mine as soon as I finish putting my belts back on and reassembling the coolant system on my car. I'm not sure if I've ever experienced my fog lights on at all. I thought in the US the rear fog light was not legal and therefore not hooked up from the factory, so I never bothered testing to find out.
 

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Keep in mind, iirc the headlights need to be on for the foglight to work.
Not if you do an easy bypass - much cooler to have the front fogs during the day without the headlights popped up ;)
 

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Discussion Starter #20
My fog lights work without the headlights on. Just have to have the running lights on.

Waxed it for the first time today. Man, that car has some lines. I guess that's why they are called exotics. Marcello Gandini knew what he was doing!
 
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