Rear Wiper (Lack of) Performance

[Rebmania]

My rear wiper stops at 10 o'clock as you look at it on the return cycle and will not run beyond that. I believe it may be time for a renewal so I replace the motor and arm (and blade) in one shot (its torn apart, might as well do it up). I fire it up, same thing with the new one. The replacement also seems to run much slower, almost like it isn't getting the power it needs. (Motor and arm are new not reman. from GM dealer) I've checked to make sure it is all mounted correctly, it does not bind anywhere when I 'help' it, and when the wiper arm is pulled back and parked off the window, it runs through the cycle and returns to park correctly. I checked voltage and have +/- 11.3 volts input on the white wire. PLEASE HELP ME!!!!!!!!

[LMP]

...model year ?
AS a starter, here is the '93 diagram, surely valid 90-96.
http://www.avigex.ca/xport/wiperrear.jpg
You should measure volage between white and black, as close as possible to motor. Ground rreturn can also be faulty.
...also this
http://www.avigex.ca/xport/wiperrear97.pdf for more recent models

[Rebmania]

It is a 1997 SE with a 3.4L in it. The voltage readings were taken off the backside of the connector between the ground (black) and line input (white). I have the diagram for the '97 wiring found on a different post. I tried to maually create a 'second' ground by running a jumper from the black to the neg. on the 12 volt outlet at the rear of the van, no difference in performance. Can I create a new ground to the roof or is there a better place back there?

[LMP]

Veryfy voltage difference between black lead at wiper unit and a known solid body/engine/battery ground. The difference should not be more than a few tenths of a volt. A voltage difference greater than that is needed to suspect a poor ground return.
I suspect 11.3 volt was mesured with engine not running....and this value is quite normal then as battery voltage is just slightly above 12V. . With eNgine running, alternator pushes voltage up to 14+ volts...possibly 14.3 or 14.5, and that should leave probably 13V at the wiper unit when in operation. 16gauge wiring is to blame for that.