72 911 heating and electrical problems

[techguy]

Hi Guys,

I have recently purchased a very nice 1972 Targa model 911T with great mechanicals however, electrically a mess! I have spent several weeks now reading about the car and learning about the electrical system. After many hours I have a great number of systems now fully operational and I am down to the last major project the heating system.

The heating system seems to be intact even with the engine change out that took place many years ago (now has a 2.7 from a 75 911S in it). The fuses are intact however, no action from the system when the fan control is moved to I, II, or III. I figure from the other posts on the board I will try contact cleaner here 1st.

Here are my questions:

1) The lights on the heater control panel are missing, what do they do and should I have lights on the left and right sides of the panel? I have several wires hanging from below the panel and have eliminated the fogs, rear defrost, lighter and speakers from the mess. I figure someone hacked the original wires to wire the radio. The mechanical controls are intact and work perfectly.

2) Where is the blower motor/motors? I have located one motor in the front trunk on the air intake housing and assume it is for the fresh air supply. Should this car have a second motor in the engine compartment? The heater lever works and the flapper boxes look intact.

Where do I go next??

[911pcars]

The instrument panel bulbs for the gauges are accessed from the trunk. The heater control bulbs are accessed under the IP. They indicate blower motor speed; 3 speeds. I think those are the only lights accessible from below.

Unless you have A/C, there is only the one blower motor in the vent system. If you have A/C, the additional blower motor is in the evaporator housing in the "smugglers" compartment. I think some 2.7s might have a heater blower motor in the engine compartment. You'll know it if you have one; it's large and ugly and doesn't look like too much engineering thought went into sticking it there.

If you need the factory wiring diagram to identify wire color codes, there might be an appropriate downloadable file on my website. Early 911 wiring didn't change too much.

Hope this helps,
Sherwood Lee
http://members.rennlist.org/911pcars

[304065]

Get yourself two beers, an aspirin and a flashlight.

Put the driver's seat all the way back.

Then, lay down on the seat with your back to the floor. Inch your way forward so that your head is even with the gas pedal. You have now assumed the "Inverted Yoga Position." This is CRUCIAL for all early 911 electrical system repairs.

With the flashlight, look upward: on the starboard side of the heater controls there should be a bulb holder where the light for the controls goes. Verify that it's not melted. There should be a wire to the bulb, yellow with a red stripe, and a brown ground off the other side. Very important that the ground runs, along with about five other brown wires, to a metal tab on the body sheetmetal. Into the switch there should be some pretty fat white, white with yellow, and white with green, although these may be inside of some tape. Anything else is superfluous, although you should NOT remove any wires from the system without first verifying that they aren't used in any other circuits, e.g., if you removed the fogs and cigarette lighter wires, you won't have power to the heater blower. Power comes out of the fog switch and goes to the hot terminal of the blower, then each speed of the blower has a separate wire that goes through the switch which "makes" with the ground.

Once you get it all fixed up, then it's time for the beers and the aspirin: lying under the dash, while good for your Karma, is murder on the back.

Good luck! We need some pictures of the underdash area if you are so inclined.

[304065]

Here's a clip from the big one on the main board in case you don't have it.

[47silver]

if your front blower motor does not work you can take it apart and clean or install new brushes. i cleaned mine and it works but i will need new brushes soon. it is not a hard project just be careful when removing the c clips on the plastic blower duct as you do not want to lose them. i used a lot of silicon spray and i would also recommend electronic cleaner

gary