I've been having a intermittent problem on my wife's 91 940. The alternator charges at random along with erratic dash lights (charge, oil, etc.). It had gotten so that none of the dash lights would illuminate, and the alternator was very un-reliable as checked with a volt meter. Sometimes charge, Sometimes no charge, with only the headlights to indicate (she goes to work before daylight), which is not a good situation. Yesterday I took the instrument cluster out to investigate. Upon inspection under a magnifying glass, I couldn't see any defects in the circuit board. On a hunch, I re-flowed the solder on all of the connectors and reinstalled the cluster. After I plugged it in, I turned on the switch and all of the indicator lights now work and the alternator is charging properly. A word to the wise. This car has a high dollar 100 amp alternator. I almost ordered a new one before I decided to look further. If you have charging problems, don't always assume that the problem is in the alternator.
Hope this helps
steve