I will bet a nickel that the car’s electrical system was fine, and that the only problem was that the connections on the battery were loose.
The terminals do not even need to be very loose for a car to not start and for the electrical system to seem dead.
Hell, I’ll bet a dollar.
dangit, I hit POST too fast…
Reversing polarity, in 99.99% of cases, will not fry a car’s electrical system. The worst it will do is blow your fuses, which can be replaced for less that $10.00.
Hey bo read post #11.
I can assure you that I know a loose battery cable when I see it. Also where there is a large hole where the alternator diode used to be is also a clue.
Actually, it’s very simple: just add a series diode. It would only cost about $1.
The reason most components don’t include a series diode is because it would increase weight, volume, and (most importantly) it would decrease efficiency. (A diode dissipates heat when current flows through it.)
I have also seen a vehicle which was fried due to reversing polarity. About a $1000 later it was fixed.
As for the cig lighter and radio, have you checked the fuses? On some cars, at least, those two accessories are on the same circuit. My car is one of them.
Of course all cars are different, but I know that if my lighter and radio were both not working at the same time, I’d be pretty confident that fuse #22 was blown.
Sounds like your guilty party right there. I wonder what the liability would be in a case like this?
Also…wouldn’t the faulty hookup blow out the good car too? It seems like in all the examples given here, only one car was affected.
He might have been color blind. I have a buddy who is completely color blind (he sees nothing but greys). Of course, he knows this and would never attempt car repairs because of it. 
Rick and I have 70 years professional auto repair experience between, and (daring to speak for both of us) we say that claim is absolutely wrong. Let us know if you have evidence to support it.
No. That’s simply a matter of where in the ground side of the circuit the negative jumper cable was connected, the dead’s car’s negative battery terminal or some grounded part of the engine on the dead car. As mentioned in posts # 6 & 7, it’s an issue of safety protocol and WILL NOT do electrical damage.
It could, but in cases where the donor car has full voltage and the non-starting car has little or none, only the latter is realistically vulnerable.
Gary You may dare to speak for me anytime. 
We are in complete agreement here, a loose batt cable could cause these problems, but I refuse to believe a 99.9% without one hell of a cite.
OK, thanks all. I’m sure that reversing the polarity is indeed the cause here.
As I said we’re gonna take a look at the insurance policy this coming week and call them to see if this is covered at all. But I don’t suppose there are any insurance experts in here with any comments?
I bow to Gary and Rick’s expertise and promise to stop posting after I work a 16 hour day. Sorry for my poor reasoning skills. I throw myself under the bus, to save anyone else any trouble. :smack:
What I meant was, it’s likely the Good Samaritan guy who switched polarity and blew out the car’s electrical system, as opposed to the professional tow truck driver. I didn’t mean to suggest that directly hooking up the batteries had anything to do with it, sorry for the confusion. (I was just thinking of how PISSED I’d be if some do-gooder who can’t tell black from red blew up my car like that, especially since I don’t have comprehensive insurance…)
I’m still having trouble understanding why the good car is less vulnerable than the bad car…does the voltage in the battery serve as a “buffer” somehow? (Granted, my knowledge of electricity is limited to knowing how to turn on a light switch…as if that wasn’t already obvious. :))
See if this analogy helps:
Two people are standing one behind the other, left hand to left hand and right hand to right hand. The stronger one is helping the weaker one push something. (These are batteries trying to run the starter.)
Now one of them turns around. They are oriented left hand to right hand and right hand to left hand. They both push. The stronger one pushes the weaker one down. The weaker one is hurt. The stronger one was pushed on, but probably was not in any real danger of being pushed down. (When connected with reversed polarity, the batteries are working against each other and their respective electrical systems.)
To clarify, I meant to say in that second part that one of them turns around so that they are facing each other.
Is there such a thing as a car where the electrics are postive earthed? I used to do security patrol in my university and we had a system for starting dead batteries. This one time, there was a guy with a little two-seater sports car, and he wouldn’t let me go near the battery of his car (which was under or behind the driver’s seat IIRC) because he said it was the opposite of the normal polarity and I would wreck it if I connected it up the wrong way.
To answer this question you should model the situation using a 1st-order approximation using source voltages and internal resistances.
Let’s assume the following:
Good Car
Open circuit battery voltage of good car: 13.2 V (I am assuming the good car is running)
Internal resistance of battery in good car: 0 Ω [sup]a[/sup]
Maximum current rating of alternator: 80 A
Dead Car
Open circuit battery voltage of dead car: 1 V
Internal resistance of battery in dead car: 0.2 Ω
Current: 71 A
Voltage across battery terminals in good car: 13.2 V
Voltage across battery terminals in dead car: -13.2 V
[sup]a[/sup][sub]The alternator in the good car has a voltage regulator. As long as the current is less than 80 A, the regulator will maintain the voltage at 13.2 V. This means the effective internal resistance is 0 Ω for the good car.[/sub]
As you can see, the voltage across the battery in the good car is a happy 13.2 V, but the voltage across the battery in the dead car is -13.2 V.
Now let’s change the internal resistance of the dead car’s battery:
Good Car
Open circuit battery voltage of good car: 12.6 V
Internal resistance of battery in good car: 0.005 Ω
Maximum current rating of alternator: 80 A
Dead Car
Open circuit battery voltage of dead car: 1 V
Internal resistance of battery in dead car: 0.15 Ω
Current: 90.3 A
Voltage across battery terminals in good car: 12.55 V
Voltage across battery terminals in dead car: -12.55 V
In the above example, the good car’s alternator is sourcing maximum current (80 A). Current is also being sourced by the good car’s battery.
At any rate, the voltage across the good car will never be negative. While this is a good thing, reversing the battery cables can still be taxing on the good car for two reasons:
Yes, old British cars used a positive ground (or earth in Britspeak) systems. The car you are describing is a pre 1968 MGB.
At least some American cars from the 50’s and earlier also had positive ground systems. The British, in keeping with their typical pace in breaking traditions 
, held on to the design into the 60’s, as Rick mentioned.