1970 rear Defogger switch Bad or Ok ?

[Bill Balkie 24172]

Hello ,
    My rear Defogger does not work on my 1970 Cadillac .  I am not an expert in automotive wiring . So I want to start with the Switch in the dash . I removed the switch after gluing  two strips of rubber to a pair of vice grips. The switch was easily pulled out of the dash board without damage to the switch . Working with a test light I first checked to see if the switch was getting power and it is .  I have attached a rough sketch with the results of my test .  With the switch off I have power to the switch  with no power coming out of the yellow and yellow and black wires . When switched to low I thought  only one wire would be delivering power . I have bright test light  on the yellow and black . Very low light coming off the yellow wire .  When switched to Hi I have a very bright light from the yellow and black and a bright light on the yellow wire  . My question is does the switch look OK  ? If it does my problem might be at the motor
End . Any advice will be appreciated.
  Thank you very much,
             Bill

[76eldo]

Bill,

Your testing process seems to show that you have power in and out of the switch.
I’d go to the rear blower and disconnect the connector see if your test light works at the connector. If it lights up and you have voltage at the connector  try putting  12 volts to the motor to see if it works. It may be the actual blower motor which can be replaced. Could also be a bad ground at the motor.

The next step involves laying in the trunk on your back to test the motor or remove the assembly and test it on a workbench.

[Jeff Rosansky CLC #28373]

Before you pull the motor do a couple of quick things. Turn it on and place your hand on it. Does it vibrate like it's trying to run or getting hot? Then run a temporary ground to it and try. You can use a piece if wire or if you don't have that available just clamp a jumper cable wire to it and a good ground. It is just s quick and dirty test.
Jeff

[Roger Zimmermann]

Indeed, on my '72 CdV I have the same situation. The switch is working as it should, I have current coming at the motor, but it does not turn. I will do the checks suggested by Jeff.
If the motor is bad, it requires the removal of the rear seat to get at it...

[Bill Balkie 24172]

Hello,
     I decided to remove the defroster unit.  from the car . You can get to the unit from the trunk . Disconnect the yellow hot wire and remove 4 screws and the unit is removed from the trunk area .  The squirrel cage fan
Was a bit tight but I could move it with my hand very easily . I looks like it is a sealed unit however l Added some lubrications oil CR36 onto the shaft and the fan moved freely . I hook up 12 volts with an extra battery I had the motor turned freely . I reinstalled it in position and hooked up the hot wire and ground . Turned on the ignition and the fan works perfectly on both high and low speeds . The bottom line was the fan was not used for several years and just needed some lubrication . It looks like the climate control work great . All windows and power locks work fine . Seat functions as it should . Radio works fine After replacing speakers  I purchased from S/M electronics .  My only other problem in getting the rear courtesy lights to come on when I open the doors .  I have power to the lights the ground seems to be the problem .  Still trying to figure that  one out . And one other thing . The emergency brake does not release on it’s own .  I have to use the auxiliary release handle .  I hope i will soon figure this all out . But to tell you the truth it’s fun trying to fix these little problems and so satisfying when we figure them out . It’s how you bond with your car .
      Bill

[Roger Zimmermann]

Probably mine has the same issue. Unfortunately, there were changes between 1970 and 1972: the motor from my car is removed from the passenger compartment. Something for next year as it's now too cold in my garage.

[76eldo]

When I first got my 70 Eldorado the rear defog did not work.
I didn’t do anything about it at the time but when I tried it again months later it did work so I think the motors get stuck from lack of use.

I’d love to see your 70 at some point.

Brian