Warning lights - what does it all mean?

Toby Price · 11-28-2002, 11:33 AM

Hi
I've got a 1982 UK spec 930 Turbo which over the last couple of days seems to have become inhabited by some strange electrical gremlins. Basically two things have happened without warning:
1 - the battery was flat one warning. A jump start and all has been well since. I've checked for excessive battery leakage & all seems well now
2 - the low charge generator AND brake warning light occasionaly come on at EXACTLY the same time. So far I've noticed this happening in stationary/slow traffic & never whilst on the move. I've disconnected the low level brake fluid sensor without effect. I've noticed that if I rev the engine above 1500rpm that both lights go out, suggesting a charging problem. If I let the revs drop then the lights stay out for some time then come on again. I've checked whether the generator is charging and it seems to be delivering 13.5 volts under load, though of course I haven't managed to check this reading whilst the generator light is on. I'll take my tester with me so I can measure this gremlin when he re-appears. That's about it. I'm sure there's a sensible explanation, though with electrics, you never can tell. Ladies & gentlemen, the ball is firmly in your court....

bell · bell's Garage

it sounds like your battery may need replaced, and possibly the alternator.
if your battery needed a jump chances are it either had/has weak cells (or wasn't getting a proper charge) and could be overloading the alternator which can eventually burn it out (which may also be why it's not keeping the voltage up at idle, causing your warning lights to come on).
i would have the battery load tested and also make sure that none of the cells in the battery are dry (if it doesn't have the "caps" on top you can't check this).
also check to ensure your v-belt it tight, if it's slipping it will keep the alternator from charging properly.
this should give you somewhere to start.

Toby Price · 11-28-2002, 02:12 PM

Hi Bell
thanks for the rapid input - but why does the brake warning light come on as well???? I'll get the battery load tested tomorrow - that should at least test that possibility out.

Face · 11-28-2002, 02:50 PM

Toby,
It could also be a bad voltage regulator. I'd monitor the system voltage while driving at different speeds with a volt meter - I had similar problems a few months back. Bought a cheap cig lighter plug insert with alligator clips from radio shack and hooked a digital volt meter up to that. Turns out the VR was going - half the time it didn't charge at all (killing my battery too), and the other half it surged 15.5V through the system (illuminating my seat belt light at odd times).
I went ahead an bought a rebuilt alternator and new VR, installed them myself and have had no problems since.
Hope this helps.

bell · bell's Garage

i beleive the car tests the brake cirquit everytime you start the car, if the voltage is dropping low enough it may be resetting the module causing it to "test" itself, i'm not an expert on the brake light cirquit though, i may be wrong, someone will have an answer for you, the guru's on this board are probably all eating turkey