OK, So I pulled the wiper motor on a 1999, There's a harness from the car going to a black box that mounted to the Wiper Bracket, the wiper motor harness also connects to this Box.

I took the wiper motor ( gear box really) apart, cleaned it and greased it up. It was definitely frozen.

I can put voltage to the red wire and Blue wire on the Wiper motor and it functions fine.

Problem is, it doesn't work in the car. That black box has two relays in it and some circuitry, It all looks clean.
The 15 amp fuse for the RR WIPER is good.
With the rear wiper turned OFF I am getting 12V to the orange wire, No voltage to any other wires in the cars connector, Nothing changes at all with the rear wiper turned to LOW or HI.
Can someone tell me what's supposed to be happening and where else do I look for why I'm not getting this wiper to work with the switch?

 

Have you tried checking voltage on dark green wire when operating the switch, you should have 12v when switch is on. If you do Id check your ground and the rear window cut out switch and make sure those are ok.

 

OK, I'm crazy.
Using both a Meter and a 12 V light, I went through the car's connector and I posted those results.
Attaching the motor and Box to the harness and running a ground wire to the Cars chassis I got nothing. No voltage on the green wire.
I put the motor back in the rear door and put everything back together except the Door panel, Just for giggles I turn on the switch again and it's working. While it was working I went to the back and wiggled wires and connectors.. all is good. Intermittent works as well as the regular 'HI'. I guess Something wasn't grounded right during my testing. Any way, a good day.
Even though I'm working on amanual pull cable for the 4WD front engagemnet, I changed out the 4WD actuator ( i got it for free), painted the Battery tray while it was out, threw a new vacuum line on that canister in the fender, replaced a front head light bulb. ( those lenses don't pull out as easy as they should things are a bit tight). not to mention A bit of a game getting the lower 'pin' back in the sheetmetal cutouts too. wouldn't want to do it in the dark.
Gee , I love when my daughter comes home from college for the weekend with her Blazer.

 

Where are the ground connections ? What wire color should be grounded ?
I have a 1999 Blazer and the rear wiper has not worked in 7 years...

THANKS

 

Here a schematic of a 97 S10