I've had this thing out and bench tested it several times, always the same, works fine on the bench but not in the car. I have now discovered that there is only like a volt and a half on the red wire going to the wiper door switch, and when I put the meter on it, it quickly drains that off to 0v. All fuses are fine, I checked them all with the meter.
I was working on putting the dash back together a couple weeks ago, and was checking operation of systems as I went along. There came a point where I only had like five volts to some of the systems, then nothing. I found that the right side of the fuse box didn't have any power at all to it. Out of curiosity I cycled the power window on the drivers side and it worked, I then noticed that the fan motor was running, I checked for power at the fuse box and viola, all systems go. I just went out and checked the fuse box, no power on the right side again, I cycled the passenger window and viola, power came back. Where does the #12 wire in diagram below get it's power from? And why would cycling the windows cause it remake connection?

 

If #12 is supposed to be always hot, there are only 2 places it can get its power from; the battery, or from something directly connected to the battery (unswitched) like the alternator or the starter.
Here's the PW diagram

 

Thank you for responding, and trying to help, but I don't understand how the diagram explains any of my questions, or the insane electrical conditions I'm dealing with

 

You've got a lot of moving parts going at once and the symptoms you note may be manifesting themselves far from their origin, such is the nature of common grounds.

I've had this thing out and bench tested it several times, always the same, works fine on the bench but not in the car.
I'm not sure what this means you have tested.

Finding out why there's not power to the hot side of you fuse block is pretty straight forward if tedious. You'll need the factory wiring diagram, if you don't have it shoot me an email.
The PW switch may be a clue or a red herring. Possibly there is a crossed wire energizing/backfeeding (why you have very low voltage at the wiper switch/relay?) other circuits when you hit the switch.
Probably not good for the longevity of the switch or relay.

 

I don't think the photo above will help you much, it is from a Late 1977 dash harness.
The wire labeled #12 is part of the forward lamp harness and lands at the alternator.
#12 wire does NOT power the wiper fuse on the Late 1977.
Feeder Buss and wire labeled #15 does.
#15 is a Brown #12 gauge wire and is HOT when ignition switch is in the ACCY or ON position...
Try moving your ignition switch between the ACCY & ON positions, you may have a ignition switch problem?
Hope this helps...

 

On a 71-

Have you checked the switch under the dash? see below
Constant power (red) for the wiper motor/firewall switch comes from the horn relay junction -
Inside the car- wiper override/service switch is powered from a junction of ignition and headlights.

The wiper motor needs two sources of power to operate- the yellow (from the fusebox acc & ign switched) to operate the solenoid
And the constant power through the firewall switch which comes from the service switch under the dash -that actually powers the motor.
The wiper switch itself in the dash needs a ground for the switch to operate.

The Blower motor shares the ground with the wiper.
So no ground there and power will backflow through the blower motor. Traveling through a "long wire" inside the motor will create resistance - and show the 5V you are seeing.

My guess- no ground for the dash- wiper switch and/or blower motor
And the service switch under the dash is turned off.

 

I'll try to keep this short.
That diagram I was referencing confused hell out of me and I was looking at/testing the wrong side of the fuse box...please note that my ego is killing me right now
So I started over, first I made sure the service switch was in the correct position to feed power to the motor. Next, I put a spring clamp on the wiper door switch and checked for 12v on both sides of it, all good.
Next, I checked for 12v on the center post of the terminal, good to go. Next I checked for proper ground to the case of the unit, good ground there. I turned the key to on position, moved the wiper switch to low, and no go.
Next, I pulled the three wire terminal off at the motor and checked for proper grounds in relation to switch movement, all good there. My next thought was, "there has to be something going on with the motor", so I pulled it out of the car AGAIN

I removed the cover/pump, pulled out the park mechanism and the three terminal connector to find the hot wire to the solenoid hanging loose. As I was soldering it back in place I noticed it's neighbor was hanging by a single strand of wire, so I re-soldered it too.
I hooked it to one of boat batteries under the bench and ran it through high, low and park, it worked perfectly. I reinstalled it in the car and viola, it works like a charm
I have another question, does anyone know whether the that hard wire coming off the resister is supposed to connect to something? See pic below.
Thank you all very much for helping me out of another one of my rabbit hole adventures. Oh...and happy new year!