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Discussion Starter · #1 ·
I have a few annoying electrical problems, none that affect the running of the car. The latest one I'm trying to resolve is why my heater fan won't run. I have traced it down to the switch behind the dash.

The problem is that I have a wiring diagram but not a schematic. I don't know what voltages are supposed to be on what wire when the switch is in a particular position.

Do schematics exist? Or have any of you figured out how to diagnose this problem.

Thanks.
 

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Try getting a wiring diagram one from Year One or OPGI. They have really good ones that show what wires go where and on my '70, it tells what position the switch is in and the wires that hook up to it. It also tells the proper guage wire too.
 

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RD
The following should help. Power/voltage is applied to the switch via the brown wire. With the ignition switch on check for voltage if none check fuse. With the switch on low you should have voltage on the yellow wire. With the switch on med. You should have voltage on the lt. blue wire. The yellow and lt. blue wires attach to the resistors mounted on the heater box. There are two resistors one for each speed, low and med. They connect to the orange wire it returns to the switch where it connects is a second orange wire. With the switch on high speed the resistors are bypassed voltage is connected directly to the orange wire. The second orange wire is routed through the bulkhead connector to the blower motor. If you are getting voltage on the orange wire and the blower motor is not running, check the ground connection at the blower motor.(my cars have A/C the blowers are mounted on a fiberglass housing. Cars with heat only I think the blower is mounted on a metal housing so blower ground should not be a problem) If all checks good, you likely need a new blower motor.

When measuring voltages you will not read less than battery voltage at any point or any speed selected, unless the blower motor is running. Without current flowing through the resistors you will not have a voltage drop across them.

Hope this helps Elree
 

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Discussion Starter · #4 ·
Elree,
I am going to run right down to the garage and try all that you have suggested! Thanks a bunch.

Here is what I found the first time....

I know the motor is good as is the ground. I put 12v right to the motor terminal from the battery and it spun fine. I also measured 12v at the brown wire at the switch behind the dash but I was not able to get any reading on any other wire. I removed the little circuit board and cleaned the contacts. I placed the pcb near the slider to see how the part worked and was puzzled. The slider seems to be aligned to get right between the contacts. What I am afraid is that there is another piece that sits on the slider that touches the contacts.

I'll let you know what I find this time around.
 

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Discussion Starter · #5 ·
Erlee,

Your information was invaluable. I removed the connector from the assembly behind the dash. With the ignition on, I jumpered the brown wire to the the others and the fan ran as intended (slow, med, high).

Clearly the problem is in the slider mechanism. I'm afraid that my earlier hunch is true. There must be a piece missing that attaches to the slider and provides contact. I see no other way for it to work.
 
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