Electrical system issues after battery cables on the wrong terminals and then for the jump start from jumper cables and put them on the.

MASP75

MEMBER
2008 SUZUKI FORENZA
2.0L
4 CYL
2WD
AUTOMATIC
92,000 MILES

The battery was weak so I went to change the battery and I put the cables on the wrong terminals and then for the jump start from jumper cables and put them on the wrong terminals. Now all the lights are lit up on the dashboard and the alternator is no good. There's also a hundred watt amp on the positive battery cable that I fried. I don't see any other fuses fried. The car starts when I charge the battery now but the radio is not working. So I did the very least I know I need an alternator if I change the alternator and the hundred watt amp will all those lights on the dash go off and is it going to solve the problem? Or could I have made a big mess of the electrical system in the car?

1 Reply

CARADIODOC

MECHANIC
33,871 POSTS

Suspect a big mess, but there is hope. Before you assume the generator has been damaged, there will be a very large bolted-in fuse that will be blown. All AC generators use multiple diodes which are one-way valves for electrical current flow. Those block current from discharging the battery when the engine is not running, but when the battery cables are reversed, those diodes become "forward biased", meaning they act like a piece of wire and in effect are a dead short. The extremely high current flow will blow that large fuse usually before it can damage and short the diodes. It is still possible one or more diodes are shorted, but don't assume that yet.

The dash warning lights tell you the computers for those systems are shut down. All computers have diodes built in that don't do anything under normal operation, but when the battery cables are reversed, they too become dead shorts and force the fuses to blow, thereby protecting the computers from very expensive damage. There are certainly going to be multiple blown fuses, so be sure to check the under-hood fuse box and the one inside. Also, a lot of import radios have a red ten-amp fuse on the back of the radio.

Here's a link to an article about testing fuses that might be of interest:

https://www.2carpros.com/articles/how-to-check-a-car-fuse