Hi.
I have just purchased a 1991 740GL 2.0L On the way home it stopped. The battery was flat. Oh, bother said I! Fitted a reconditioned alternator still a flat battery. I then noticed that no warning lights were working, apart from the seat belt warning lamp. Next day I had to move the car, now all the warning lights work and the battery charges. 4 hours later I had to move the car back, no warning lights again. This is the trend, obviously the car is useless in its present state. What the hell is happening? I thought these cars were supposed to be reliable! Comes to something when I have to fall back on, dare I say it my ultra reliable Renault.
I would very much appreciate any suggestions.
Thanks, Pete.

Does the Battery (not charging) Warning light come on when you turn the key on to position II?

It should because the Bulb (and 3 others) are grounded (earthed?) via the Alternator and it's ground wire. (On 240 Bosch alternators its a small red wire to the D+ terminal.)

This "pre-exitation" current from panel light thru alternator to ground is essential. The alternator can't develop voltage without it.

Check for that wire, and the alternator grounding wire.

If those wire are OK, the Voltage Regulator and Brush unit may be wearing out.
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

Bruce.
I have just found the problem. Under the dashboard should be a plastic panel, this is in the boot! The reason is that if you stuff your hand up amongst the wiring and wobble it about the warning lights flicker on and off. So if I locate the loose wire the problem will be solved, hopefully. Whilst I held the wiring in a suitable position to get the lights on my wife ran a volt meter from the thin red wire on the alternator to earth and there is a voltage. I will fix the wiring and leave it running a while with all the lights on to see if the battery runs flat or not. the cowboy who sold me the car obviously new about this problem.
Pete.
P.S. I've now had the engine running for an hour with all headlights, heater, fog light etc... on and its still running with the alternator showing 14.5 volts and the battery showing 13.5 volts.