Electrical Issues...???

[skybandit]

Ok,I thought the problem with my 91 n/a was the alternator(car wasn't keeping a charge),so i changed the alternator(got a new 80 amp from Toyota).Well,lo and behold,the dang thing still won't keep a charge.What the f...can be the problem?The battery has less than a year on it and the car hasn't been driven more than 400 miles the whole year so I don't think its the battery.Does anyone have any ideas as to why this car won't keep a charge?When its running the car drives great,but the voltmeter will flucuate when you turn on the lights,the heater,roll down the window,etc.After the meter drops a little when you do any of the above it then returns to almost the top.If its a short somewhere I have no idea how to check to find the source of any potential short,any help on that would be cool.The only thing other than a short that i can think of is one time my wife had to jump the car and after hooking the cables to the jump car she accidently switched the cables on the MR2's battery(red on black,black on red..yikes!) Of course the spark that occurred when she did this led her to believe that she had made a tactical error so she corrected this and got the car jumped.My question is,could the battery be damaged internally from such an act and should I just get a new battery or switch one from my Corrolla just to see what happens?Thanks everyone for any help,Pete.

[Ironmike4x4]

I have seen incidents in my shop where people have swapped battery posts and have some negative effects such as blown fuses or batteries just die. You said you checked with the voltimeter... are you getting a charge of more than 14.0 volts? If so then sounds to me like the voltage regulator is bad. If normal I would just swap batteries just to find out, but also check to see if you have a parasitic drain somewhere.

[MitchB]

Batteries can and do go bad sometimes in short order. Try swapping your battery with somebody else for a few days.

Or, go to a parts store and have them test it. (Usually a useless waste of time.)

Or, go buy a new one!

Nice to know that your alternator should be good for many more years, right?

[skybandit]

Ok,this was pretty dang simple.I swapped my battery from my Corolla into the MR2,turned the key and the sucker fired right up!I then put the battery from the 2 into the Corolla and of course the car wouldn't start,so I guess it was the battery all the time.Oh well,I learned from this fiasco that maybe you should go for the obvious,lol.

[Gairloch]

Good rule for diagnosing stuff. Always start with the simpliest most easily repaired possibilities and go from there.