Speedometer problem '89 740 GL

Picked up a 1989 740 GL FREE off a parent friend, couple big problems, lots of little ones (cosmetic) slowly in the process of Customizing what i can, but ran into a small problem.
When i first recieved the car two of the problems were bad break (cracked rear piston) and the Speedometer didn't work. I have the Chilton/Haynes Repair Manual but its for multiple models from '89 to 9* and the wireing diagrams seem to be incomplete it goes into most of the system electrical but the only block for the instrument panel doesn't have the schems to figure it out. Also the rpm-o-meter works fine so i'm wondering if its electricle, any ideas or help is greatly appreciated, even for other models, at lest then i can get an idea (and could save me the time/money of having a pro fix it).
Other instruments not working or havn't moved are, Clock, Fuel level, tripometer.

Thanks in advanced

Book mark this link. Tons of Volvo info.

Brickboard (http://www.brickboard.com/FAQ/700-900/)

Yes the brickboard has a load of information that may help.

The 700 series speed is electric and runs off an impulse from a sensor in the differential, the clearence between the sensor can become covered with sludge and metal filings from the diff, and the impulse ring / sensor gap is critical.

Awsome Thanks, so far the brickboard site is the most informative site i've seen on the740 thanks.

How do you clean the sensor? what does it take to remove it and clean it? i have a '90 740 gl that i am trying to get the speedometer to work. i have replaced the old one with a speedometer that was working.