Hi: I hope I can help you. If its like my 88 740 GLE wagon, this is what to do. Gently pry up the cover at the end of the wiper arm,it should swing up out of the way. Next , there should be a nut under that cover, remove it turning it counter clockwise. Next, pry up on the underside of the end of the arm and wiggle it pulling it towards you to get it off the splined shaft that its mounted on. This may take a little time ,but you can do it.Once you have the arm and blade off as one piece, turn on your rear wiper and watch the splined spindle turning back and forth, then have someone shut it off. When it comes to the stop mark it with a piece of masking tape or something so you will have a refferance point in the stop position. Next , have someone turn it back on and let it run a few turns ( watching the spindel ) then have them turn it back off. This will be the start position. Now put the wiper arm back on the splined shaft and remember to put it pointing on the left or right side so that when its turned on WHEN YOUR FINISHED it will swing up the rear glass. Push the arm down the splined shaft as far as it will go,when its all the way down you will know because the threaded part of the splined shaft will be sticking up enough to install the hold down nut. Now tighten it down nice and very snug,swing the wiper arm cover down over the nut. Now test it, spray some water and turn it on let it run about 7 or 8 stroks spraying washer solvent on it so you do'nt rub the wiper blade on dry glass. Now shut it off and it should come to the stop either on the left or right. If it dos'nt someone installed the wrong motor or installed it without putting the motor in its start position. Good luck,I hope I have helped you more than confuse you. Please let me know how it worked out for you in the end, Dan Metz.
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Dan's 88 Volvo 740 GLE WAGON non-turbo