Jump Cables connected backward

[flightporsche]

While connecting jump cables to start a 1982 automatic 928, the positive
and negative were connected backward. After the sparks flew no further attempt
was made to start the car. Before connecting a new batt, should I expect
electrical damages ?

[tmpusfugit]

I bought a '84 that had the battery in it wired backwards. When the owner attempted to start the car it broke the timing belt immediately, but he didn't know that when he sold it to me. He didn't even know the battery was in reverse connected. After I corrected the timing belt problem with all the usual parts and installed a new battery the car started right up. The alternator was not working (toast) with several blown diodes/or burnt out windings...as the car had been sitting for a long time I had to clean all the grounds, clean all the fuse contacts, replace several light bulbs etc, but when finished pretty much everything worked other than the clock and cruise control. So, that was my results, and I considered myself very lucky....YMMV

And that car was a perfect example of never take a sellers word for anything...it was sold to me as "OK engine, was running but needs a battery"....and I was stupid enough to take their word for it as the seller had a huge collection of vintage cars he had restored completely, why would he lie? We live and maybe learn, I guess I rode the short bus for a reason?

[MPDano]

I remember my buddy doing that when he was totally drunk, I think he fried the other persons battery. Not sure if any other damage happened since they never said anything afterwards.

This was not a 928 by the way.

[flightporsche]

Connected recharged batt, check for damage and started engine. everything seen fine.
thanks for the sugestions.

[Mrmerlin]

the WSM says not to jump start the car use a fresh charged battery only.
you should check the alternator output at 1500 RPM it should be over 13.5 its under that then you have atleast one blown diode in the alternator and the battery will not be able to be fully charged by the alternator.

Always charge the battery first before testing,
the alternator is not made to recharge the battery

[JK McDonald]

Mrmerlin, I was surprised when I had found the WSM factory recommendations about trying to jump start a 928. This may well be because of the length of the positive cable that delivers power toward the front of the car. A newly installed charged battery may also make an owner remove the cables and check for any contact corrosion. We have all seen the assortment of problems that can result from a poor electrical connection on our cars.

Hey MPDano, One of the weirdest things I have ever seen happen was years ago when me and a buddy were trying to jump-start an old pick-up truck that had been given to him. It had originally belonged to a great uncle and unknown to us was appropriately wired up (for the year) with a positive ground battery system and a humongous 6 volt generator. Since we were just kids, his dad had come out to supervise the project with a pair of jumper cables and his new Pontiac. With the 6 volt battery completely dead, except for a drop in the Pontiac’s engine rpm once the battery cables were connected, there was no indication of what was about to occur. I found out many years later that the armature and field are series wound in a 6 volt starter. So no matter the polarity of the applied current flow, the starter will always rotate in the correct direction.

Surprisingly, the truck motor sputtered to life and ran pretty good but before we could congratulate ourselves, the pos grd 6 volt generator came online and all hell broke loose. This whole calamity of errors seems funny now cause it looked exactly like one of those cartoons where a fizzling spark runs down a long fuse heading for a stick of dynamite. At this point heavy smoke was just rolling out from every fuse panel, wire bundle and electrical cable. Then the 6 volt battery case split open with a loud Ka-pow.

Needless to say the Pontiac had a slight smell of burnt rubber after repaired and never did seem to run quite the same again.

Michael

[Landseer]

Now that would have won the $10K prize on Americas Funniest.



You used to be able to jump start a car with just 1 cable.

[Mrmerlin]

after you crashed them together

[Landseer]

Right. Rest the bumpers against each other for the ground.

But, if they are dirty, or not firmly in contact, you can weld the two cars together in the process

[Maleficio]

Crazy story. Reminds me of the dude in here talking about the engine of an old car only having the throttle cable as the block ground, and watching the cable catch fire.