Can you check a fuse wire on an 86 for me?

[M5guy]

In the front fuse box, do you have two wires attached to the bottom of fuse 8?

I have one black/violet wire, which I think powers my outside mirrors (working). This fuse is supposed to also power the center console heater bits, which isn’t working, possibly because there is only the one wire on the fuse. Suspiciously, there is a large red wire just below the fuse that is not attached to anything.

I know the footwell fans work cause I test jumpered them at the big resistor on the firewall.

So if you have a moment to check the wires exiting fuse 8 I would be grateful to you.

[wazzz]

930 or 911?

[M5guy]

930, but that part most likely same as 911.

[wazzz]

The diagram for 930 shows two black/violet wires coming out of fuse 5 of box I (the one you call fuse number 8) and a thick red wire with yellow stripe coming in. That red/yellow wire is powering this fuse and the two adjacent fuses from the ignition switch. Is this the one you are referring to or is your dangling wire really plain red? It needs to be connected.

Regarding the two black/violet wires, one is powering the mirrors as you correctly guessed and the other one is powering the heater unit between seats. It is required, otherwise no heater.

[M5guy]

Hi Gilles

I saw on the schematic that there were two black/violet wires. As I can only find one, and given that schematics are wholly symbolic, I wonder if those two wires actually represent a split later on going to the two mirrors.

Also, my understanding is that the center heat box does not go live until a thermal switch closes in the engine compartment. Is this correct?

Merci,

Steve

[M5guy]

In this photo from FCP, there appears to be a bl/vi wire AND a large red wire on fuse 8.

[wazzz]

Steve, the factory diagram clearly show two black/violet wires coming out from this fuse. One is going to the mirror switch (joystick) which then distributes power to both mirrors according to the changeover switch. The other black/violet wire is going to the heater control unit, ie the console between seats with a rotary switch. That's this wire that you seem to be missing.

Do you have a manual heater or is it automatic? If automatic the control unit reads the inside temp in the cabin and the outside temp in the heat exchanger, then it does its thing to control the heater flaps. But the heating center heat box should go live and be reactive as soon as you switch the ignition on.
How long have you have this car for and was the heater ever responsive since you bought it?

[wazzz]

Originally Posted by M5guy

In this photo from FCP, there appears to be a bl/vi wire AND a large red wire on fuse 8.

Fuse 8 starting from the left on this picture shows the large red with yellow stripe I told you about in a previous post. Is this the one you have dangling? If so you should reconnect it.

[wazzz]

I just checked on my own car which is an 88 911 and the wiring is the same. Two tiny black/violet wires are running down from fuse 8, which is also powered by a bigger red/yellow wire. See the pic I took.



Make sure the second black/violet wire is not hiding like you can see on my car. It loops back behind the fuse block and can easily be missed.

[M5guy]

Gilles

Yes that helps. Will hunt for missing wire.

Mine is automatic heat. Would prefer manual for sure, far less complicated and no printed circuit board. I’ve had the car about 12 years and the auto heat hasn’t worked. I use the dashboard heat, which is much less but adequate.

Steve

[proporsche]

Originally Posted by M5guy

Gilles

Yes that helps. Will hunt for missing wire.

Mine is automatic heat. Would prefer manual for sure, far less complicated and no printed circuit board. I’ve had the car about 12 years and the auto heat hasn’t worked. I use the dashboard heat, which is much less but adequate.

Steve

what is wrong with your auto heat?it does not work at all .have you tried to disconnect the sensor between the sun visors..?
Ivan

[M5guy]

Gilles: I found the second bl/vi wire coming from the bundle and then it disappears behind the fuse panel, as you pointed out. Haven’t found its terminus yet but I will check it today to see if it draws current when the center heater knob is turned on.

Ivan: I will disconnect that sensor today and see what happens.

[wazzz]

Good for the wire.
As for the sensor, disconnecting it won't make any difference as it cannot prevent the heater from running. When turning the center knob you should hear the servo system work. If not then something is definitely wrong inside the center console. The inside sensor is not involved in power on or off the heater. It is only involved in regulating the heating, ie closing / opening of flaps. If you don't hear the actuating mechanism for these flaps at all, something else is wrong and the sensor itself has nothing to do with it.

[proporsche]

Originally Posted by M5guy

Gilles: I found the second bl/vi wire coming from the bundle and then it disappears behind the fuse panel, as you pointed out. Haven’t found its terminus yet but I will check it today to see if it draws current when the center heater knob is turned on.

Ivan: I will disconnect that sensor today and see what happens.

the heater shiould all the way open with the sensor off...Make sure your moving rod is in place too.By removing the side cover on right even the rubber booth.

Ivan

[M5guy]

Gilles: the servo for the flaps is confirmed working today, so I don’t have a power issue. I know the foot well fans work when I jumper them, but I will check to see if their relay is getting activated.

Ivan: my car has the dash temp sensor next to the steering wheel with the sensor fan behind the dash. I’ll remove and bench test. As pictured below.

Thanks!

Ps: fan working on item below.

[wazzz]

So, if I understand it correctly, you now hear the servo running when turning the central knob to pos. 1-10, but the footwell blowers never turn on, is that it?

If so, checking the relay may be a good thing, but be aware that a bad relay cannot explain why the footwell blowers don't run on low and medium speeds, since the relay is only used for the high speed, when the knob is turned to position 10 (DEF). Low and medium speeds only use a pair of resistors and bypass the relay.

[proporsche]

M5guy ..i did overlooked the year;-) there is link here by Glen about the modify the heater relay at the engine compartment..just do not remember if 930 has it there too as carrera models..
Ivan

[LucaScali]

I can confirm that on an '87 930, the bottom of fuse #8 takes 2 black/violet wires. One of mine was hiding under the recently installed updated fuse panel. All is good now--AutoHeat is back online.

[M5guy]

Ok, thanks all.

So here is where I am:

The center console unit gets power and the flapper servo runs.
The footwell fans work when jumpered at the resistor. The high speed relay bench tests ok.
The fan on the behind dash temp sensor is running.

Any suggestions on what to check next? Maybe micro switches on the servo?

BTW, I appreciate all the help.

I suppose I could easily run a wire from a keyed fuse point to the resistor and have the footwell fans on one speed all the time. A bandage, not a fix.

[wazzz]

Originally Posted by proporsche

M5guy ..i did overlooked the year;-) there is link here by Glen about the modify the heater relay at the engine compartment..just do not remember if 930 has it there too as carrera models..
Ivan

Ivan, no. This relay belongs to 3.2 Carrera only. No such relay in the 930, as they have no heater blower in the engine compartment. Space constraint, I suppose.
So a 86 930 relies on footwell blowers for heating.