1982 Starlet electrical nightmare

I purchased this car used last year and have had constant problems such as battery draining after a very short time unused, snapping of the engine fuse disabling alternator, and car running after the key is removed. I suspect some type of short but I don't know where. I have replaced both battery and alternator to no avail. I fear these problems will cause alternator and battery to deteriorate.

Reply to
derek
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My first thought is the alternator has an internal problem like a bad diode that intermittently partially grounds out (high resistance ground) and drains the battery, or totally grounds and pops the fusible link/main fuse - Have you had a rebuild installed since you bought it? On an '82 it might be an external regulated alternator, or a first generation with the internal regulator.

One of the Dealer Techs that hangs out here may have heard of this one happening before - and on a 24 year old model, they're liable to have seen it a lot. The run-on problem could be related to an electrical back-feed from the alternator failure warning light circuit through to the ignition coil, but that's just a wild guess.

(But a lot of my 'wild guesses' tend to be close to the mark.)

Note that I am NOT saying "That's the problem, Change it" but the alternator is the first item to check with a voltmeter and ammeter to see what is going on - and check it with an oscilloscope if you have one.

The output waveform will be all funky on the scope if you have a bad diode - the alternator internally puts out three-phase AC power that is rectified by the diode stack into DC, and when you drop a phase the bad "AC Ripple" on the output line is very obvious - if you only have a voltmeter, you'll see several volts of measurable AC Voltage on the output line. The AM Radio will probably be un-listenable from alternator whine.

And get the battery load tested, and check the manufacturing date code - if the battery is old enough to be out of warranty, change it. They go bad just from old age, and the warranty date is just the median failure time they're saying you'll get past. Bad batteries can ruin good alternators, and bad alternators can kill good batteries.

WARNING: DO NOT try running the car with the battery disconnected or that main fuse blown! Depending on the design of the circuit, some alternators will go full-field wide open when there is no battery in the circuit, and they can send well over the normal 13-15 VDC out to the rest of the car (50 volts or more) which can and will fry lots of expensive things. This is bad.

If you go get the alternator rebuilt on general principles, get a proper rebuild done - new ball bearings, windings checked thoroughly, new brushes, new diode rectifier stack and new regulator. They buy the parts in bulk, so it isn't that expensive to do it right.

The chain 'Beauty Auto Parts Stores' send them out and the cheap rebuild shops they use only clean the outside, change what they think are the "bad" parts, toss 'em in a clean box and ship 'em back out... They figure the "Lifetime Warranty" will cover the come-backs.

I had one bad afternoon when the alternator died away from home and a Kr***n was the only parts store around, it took R&R-ing four [expletives deleted] alternators in their parking lot to find one that worked.

(But it was swap the alternator there or chance 50 miles home at night running only on the battery, which would be dicey. And if you stall an automatic with a dead battery, now you're in deep [stuff].)

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Reply to
Bruce L. Bergman

Thanks for the leads I will look into it. The alternators I use always come from ebay rebuilder overstocks so I don't know their background. This one has an internal regulator, as did the one I replaced. The harness plug was missing, so I actually spliced the wires ( yellow, blue, and white) color to color from alternator to harness. The battery is a new deep cycle, since I have a tendency to run its charge out. Are you saying that if I remove the warning light relay that will probably stop the ignition problem?

Reply to
derek

Only the people who did the work know whether it was done right, or done cheap... I go to the shop and can stand there and watch them work on mine, so I know. (But I usually go disappear for an hour or two - there's an Electronics Surplus Store about a mile away.)

Check your connections.

Hey, if the engine won't shut off, and you go pull the warning light relay and the engine stops right now, that's where I'd start looking for a backfeed or a stuck relay.

Or the wrong relay. There are a few odd automotive Bosch Cube style relays that are DPST 'double break' with a common hot and two switched legs, and they plug into the same socket as a SPDT - which could send power where it isn't wanted. They build some relays with a Counter-EMF diode across the coil or as an arc snubber across the power contacts. And either the diode shorts, or you aren't supposed to use one with a diode on that circuit, or you ARE supposed to have the special relay and someone put in a plain one.

Never underestimate the stupidity of... ;-)

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Reply to
Bruce L. Bergman

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