Battery not charging

Okay, you hit the #1 suspect with the grounding wire to the block. My second suspect would be that the carbon brushes on the voltage regulator are at their limit. They're attached to the voltage regulator that's very easy to remove (two screws on the back of the alternator). Unfortunately the way Volvo wired up the battery light on the 240s the brushes are part of the circuit, so the idiot light will not come on when they're worn out (ask me how I know....)

Bill

You're right on the way the "idiot light" works, Bill. That wiring arrangement is common in cars of that era. It seemed like a good idea at the time I'm sure. The light is between the 12V bus and the excitation terminal on the alternator. When the alternator isn't working, the current flows from the bus, through the lamp, through the regulator, through the brushes and rotor to light the lamp in the process. When the alternator works, it generates its own voltage to power the voltage regulator et al and the lamp has no voltage across it. The problem was in that part about the current flowing through the brushes.... I learned the same way you did, Bill :-(

My experience is that the brushes make better contact when the engine is cold. The OP can look at his "battery" light when the ignition switch is in the "run" position and the engine is not running. He can expect to see the light sometimes on and sometimes off, which strongly suggests the brushes are worn out (as we would expect in a '93). Or he can replace the brush block - it's at end-of-life anyway - and very probably solve the problem.

Mike

My first thought would be the basics: Check the cable connections for builtup corrosion and clean as needed. Next check the ground connection to be sure road salt, etc., hasn't given you a poor ground.

Also note well that if the lamp is burned out, the alternator will not charge. You might get it started with the test lamp, and endlessly chase your problem somewhere else.

Does the lamp light up when you first turn the key on?

I almost forgot about that. Fortunately, it is a relatively rare occurance, but it can be a puzzler when it happens. Frustrating, too.

Mike