Volvo: 93 Volvo 940 Electrical, fuel guage, volvo radio

Question
Hi Ray,
I recently bought a 93 940 GL.  Fantastic little car (even with a worn auto trany). One BIG problem: Fuel guage indicates good fuel level at cold start-up, then after some running time nose dives to below empty.  Happens quicker on a full tank and on HOT afternoons (115F+ here in central Texas).  On cool mornings, I can go ten to fifteen minutes before it plunges, same if I let the level go down around half a tank, but within five minutes in the afternoon/evening on a full tank.  Stays on empty on hot start-up after five or ten minute shutdown.  Any advice would be greatly appreciated. Have heard/read about pump/float in the tank hanging, but float reostat wouldn't be heat sensitive, would it and this doesn't sound like a hang to me?  Previous owner replaced Volvo radio with Audiovox, appearing to butcher the iwring in the process, but most everything else works. Also heard about grounding problems on bricks (sounds like an excelent candidate to me), but where are the ground points which might affect the fuel guage (only one with a problem)?  Sorry about being so verbose, but I thought more info might help.  Where do I start? I bought a Chilton's 72302 Volvo 90-98 Coupes/Sedans repair manual. What a joke, worst waste of money yet.  Where/what for an electrical manual with good (color codes) wiring diagrams.  Thanks for your time/trouble and help.
klg  

Answer
Kerry,
Take a ohm reading at the Brown and Gray/white. If the reading is missing then the sender is at fault. If you always get a reading but the gauge is not reading then you may have a gauge or the cluster circut card going bad.
Reading depends on level in tank.
Remove battery negative lead.
Unplug connector and measure between the white-gray and brown leads with an ohmmeter. Resistance should be between 0 and 280 ohm with a 60-liter tank (15.9 US gal.) .