BMW Repair: speedometer, 1985 bmw 535i, bmw 535i

Question
After a long period of rain my speedometer failed.  now after a few day of no rain it has started to work. but it takes it a period of time for it to work and it bounces around for a few minutes then it begans to read accurate.  i have also noticed for a long period of time when i start my car the abs light goes on immediatly and after having the sensor checked ..still dont no why.  first the problem with the speedometor is that possibly because of a bad abs wheel speed sensor and if so those my bmw have a front or back abs wheel sensors(1985 bmw 535i) can this also be the reason my abs light goes on, and if this is not the problem. i heard someone mention a weak signal generator, but not sure if my car has one of those, have checked my manual no mention of a signal generator..please help.  thank you

Answer
Check the reference sensor that should be attached to the bell housing, if that is within spec, check the connection that plugs the sensor to the ecu harness, it's common that it gets wet in the rain and spontainously gets a bad connection, you can dry it out sometimes.  The abs system on this car works seperate from the speedo,  i'm not sure what a signal generator is but it could be the abs wheel sensor.  check the gap (with a copper feeler gauge).  You can also put a scanner on the abs circuit to see what fault it is coming up with.
-cheers