This was happening to an '86 wagon I bought out of a field near some guy's house where it had dat form almost a year due to the battery draining dead all the time.

Turned out the ground wire on the bottom rear of the alternator was rotted off.

I installed a new jumper between that small post at the bottom rear (8mm nut) to a mounting nut on the alternator bracket.

Engine now keeps running and alternator charges.

Without the alternator "alternating", the engine has to rely on battery power drectly, which the poor thing can't supply.

Once I forgot to hook this ground back on and drove the fully charged battery about 48 miles before the dash lights all came on, leaving me stranded. It was 50 miles to home, so I walked the other two. All it was was this ground wire off.

You may wish to check/replace the alternator brushes once you get things figured out. About $4 a set, Drill out the old, solder in the new. Check the FAQ for procedure.

bad battery. take the battery to a shop or to a retailer (like autozone) who will do a free battery test to see if it doesn't have a cracked cell, etc. if the battery is bad it won't hold a charge and will drain itself rapidly. the extent of the damage to the battery effects how long it can sit before it will die.

-rt

You must have 12V available to the fuel and ignition systems for the engine to keep running. If the battery is completely flat and the alternator is weak it may not be putting out enough juice at idle to provide that voltage.

Do you have a meter?
What is voltage at your battery with key on?
Does car keep running and respond to gas pedal normally if cables from donor car are left in place? If yes you most likely have a problem in the charging system which has allowed battery to discharge . Check all connection around battery, alternator and starter, charge battery. Check voltage at battery while running, it should be at least 13.5V to 14 V with no accessories.



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David Hunter