Name this wire!

[911 Rod]

Trying to figure out how this was supposed to be wired.
It appears the wire broke at the fuse box in the engine and someone ran a loose wire.
Where does this wire go under the dash? (Black one) and what does it do?
Main power for the blowers?
I know I'm reaching here, but also know there is a vast amount of knowledge on this board.
86 911

[Uwon]

Do all lights, engine bay and footwell blowers, rear window heat, electric Windows, accessories, etc work (1) with ignition on but engine off and (2) engine running?
Then the brain trust can go from there.
Johan

[scarceller]

Rod,

What are those connectors for? Gives us a hint about what else is in the harness bundle?

They seem to have run a black power wire from the front trunk to the rear fuse, correct? That's kind of silly because the rear fuse is usually always hot (12v at all times) can you verify that the fuse at the rear has 12v with key out of the ignition. And also verify that wire up front is always hot.

EDIT: I just figured out those wires are at the rear of the cabin tunnel. The small connector is heat related for the heat levers between the seats. Do you have auto climate heat in this car?

[scarceller]

I think that larger connector is supposed to go to the heater blower speed rotary knob between the seats. Few questions here:
- Does your heat work?
- Do you still have the rear engine heat blower in the engine bay?

If you remove the engine bay heat blower the front blowers won't work, they may have hacked the wiring so they could get the front blowers to run? I suspect this may be what's going on here. Tell us more about your heat system and if they removed the rear blower?

[scarceller]

Let me take a guess here: Your front blowers only run if you put the rotary switch in pos #3, they only runs at full hi-speed? Am I correct? If so I know what's going on.

And if you put the switch in pos 3 do they still run even if the key is removed from the ignition?

[911 Rod]

Thanks for the help guys.

Yes I tested what I could and this is what I found.
With wire connected or not, everything works. Not sure about air conditioning (removed), but the blower works.
The auto heat is connected, but has never worked in the 16 years I've had the car. Unless it does and I just haven't figured it out.

Of course things always are 1 step forward and 2 steps backwards.
With my testing, I've found the engine blower is not working. (It did last year) There is 12 volts there when I lift the heat levers so I know it's getting power.
Neither foot blowers are working. Last year only the passenger one worked, so maybe it's pooched now too.

I need to pull all 3 blowers and get them working, but I'm starting to think I will never know what this mystery power wire goes to. (I will leave it disconnected)

Let's remember that wire has been there since I bought the car and the heat worked fine with it connected.

I enjoyed rebuilding my engine more than this crap.

[scarceller]

What does that 6 pin connector connect to? I think it goes to the rotary heat switch, correct?
If so that black wire in the connector is actually supposed to have 2 wires in that location. The schematic shows 2 black wires in the white 6 pin connector and both wires crimped to the same pin. You're picture shows only 1 black wire in the connector, that seems wrong.

[ClickClickBoom]

I will vote for Phil!

[911 Rod]

Yes Sal!
Connector is for the rotary heat switch and the wire is the right length to go in with the other black wire. Trying to see if there is power at the black wire at the connector (no power operating blower levers or rotary heat switch) the wire fell out I assume because it was crimped for 2 wires. So it appears the exposed wire in my original picture came out of there. Now the question is why did someone feel a need to run power to this wire. I'm thinking there should be power there already?

[911 Rod]

Going through my service records I have found from 1990.
"check and repair wiring for heating system" as well as "replace heater relay control box".

[scarceller]

So I'd put that wire back into that connector and remove that power feed. Then debug everything in stock config.

I bet someone hot wired the power to get the front blowers to work. If the rear blower does not work the front ones won't either. Fix the rear blower issue first! And put the wiring back to stock.

[scarceller]

PM me I have a good schematic for the wiring. Give me your email addr.

[911 Rod]

Joining the 2 black wires together with the power wire I can hear a relay going off.

[scarceller]

Get rid of that power back feed they did. You should not need to feed power from the rear fuse! You need to figure out why the system does not work in the stock config.

[911 Rod]

Sunday update.
Engine blower working as it should. Mystery wire or not.
Both footwell motors are toast. Squirrel cages for both melted to the housing. Passenger side wire harness turned to goo.
Power to the footwell blowers only with mystery wire connected.
"Name this wire!" Has turned into a huge project.

[911Cabrio]

The blower motor relay in the engine compartment is likely bad. Thus the reason for the "mystery wire" there is a post on bypass the reed switch internally in the relay. Or may find a replacement but they are expensive. I may have a set of footwell blower motors and possibly the relay. Bob

[911 Rod]

I wonder if bypassing is disconnecting the auto rotary heat switch would help things? What were they thinking?

[scarceller]

If the rear blower is running then that connector with the 2 black wires on the same pin should have power (without the mystery wire). If those black wires do not have power then you need to check at the heater control relay pin #4 for power.

Or better yet try this simple test.
- Remove the heat controller relay in the rear fuse tin area.
- With the relay removed bridge/jumper pin #3 to #4
- Now test if you have power at the black wires in that connector without the mystery wire hooked up.
- If you have power try turning on the foot well blowers with the heat rotary knob.
- Do you now have power at the foot well blower motors?

If jumpering 3&4 gives power to the front blowers you have a bad faulty heat controller.
You can replace the entire heat controller with 2 simple 30/40amp relays, I came up with the design for this a few years back. See this thread:
Carrera - Removing Engine Compartment Heater Blower
Post #36
That wiring schematic I designed, been using this for years in my 84, works great.

I cut my harness and put in 2 standard relay plugs onto the harness but others have gutted a bad heat controller, removed all the electronics from the controller and then wired the 2 relays to the controller's pins. Then they simply put the cover back on the controller with the new relays inside the cover. Very clever and not very difficult to do take a look at post 56 in that thread someone posted a picture.

That thread has just about everything you ever wanted to know about the heat and the 3 blowers! I have no idea why the factory made such a complicated controller? I guess they never wanted the front blowers on without the rear? That kind of makes a little sense since running just the front blowers will form a vacuum in the heat exchangers and COULD suck exhaust fumes into the cabin?

The other approach is to completely remove the front blowers, gut them out, remove the blower cage and the motors... then put them back totally hollow and just use the rear blower to push the air forward. That's basically the SC car design, plenty of heat without all the foot well blower noise. I kept the front footwell blowers but removed the rear blower, it's up to you but you really don't need the rear and the footwells, one or the other will toast you out of the car.

[911 Rod]

As most of my projects, this one grew a second head.
Engine blower is intermittent when installed, but bench tests fine and I am getting a constant 12 volts at the plug. Tapping on it makes it come alive. Connection all cleaned up. Strange.
New footwell blower in the driver's side and passenger side gutted.
Repaired connector at heater control unit at the front tunnel. It actually works, but only on #3, the highest setting.
Did Sal's test jumping pins 3&4 of the heat control module and footwell blower works.
Opened up module to find this. Looks like it has melted?

[911 Rod]

After further inspection, I have found the connection from pin 4 broken/burnt.

Can this be repaired? Why did it break/burn?