Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Dumb move...HELP! (electrical)

I foolishly reverse wired the battery last night and fried the alternator, possibly the starter and caused who knows how many electrical issues. Just wondering if anyone has made the same dumb move and could assist in diagnosing the problems I caused. my only consolation is none of the fuses blew and the car turned over for me once with working headlights and so on. I’m fairly certain I only killed the charging system but am convinced it created a short somewhere in the wiring because the headlights failed to work about 15 minutes after turning over the engine (whereas they burned bright after turning the car off). The battery still has 12 volts (checked with a multimeter) but I have no power throughout the car. Any advice would be hugely appreciated.

I’ve never done this myself, but I’ve read many posts similar to yours. You’re not the only one who’s ever hooked up a battery backwards.

Without knowing the year, make, and model of your car it’s hard to say what might be wrong, but my understanding is that on modern, computer-controlled vehicles the potential for electrical/electronic damage from reversing the polarity is HUGE.

I wish you the best of luck, and I hope someone will have a more helpful answer for you soon.

If the is no power throughout the car check the fusible links.

I Agree With Checking The Fusible Links.

Hey, Is It Possible That Any Expensive Damage Would Be Covered By Your Comprehensive Insurance? You “vandalized” your own car by accident when it was parked. Check with your policy/agent and see what your “deductible” is. I vandalized one of my parked cars. I took the rear window out by flinging a stone from the weed trimmer, apparently. I didn’t notice it until later on and figured that’s what happened when I saw the exploded glass. I have zero deductible and got a new window for free. Also, I don’t believe this will result in higher premiums like an at fault accident will.

Please let us know what happens in case any one of us does something stupid (again).

It’s unlikely you damaged the alternator. Not impossible, but I doubt it. You probably burned out one or more fusible links. You need a manual with a schematic, or just take it to someone and hope for the best.

This is a common mistake.

I suppose adding the fact that it’s a 1968 pontiac lemans might help. basic series circuitry. I know doing this is a likely cause for fried alternator diodes. also, immediately after connecting the battery with reversed polarity, there was a loud pop, smoke and toasty warm cables. Also the “GEN” warning light was lit in the dash. I can almost guarantee the alternator blew but my concern is other damage to the starting/charging system. As I said in my first post, the car started and ran, then didn’t start, then lost all electrical power on separate attempts with no change to the system. the battery has been tested and is still good and again, all the fuses are intact.

As you noted, there is almost nothing, besides the alternator diodes, that give a hoot about the voltage polarity. A capacitor here and there is about the only thing that would be adversely affected by reversed polarity. Where would they be? In the distributor primary circuit? The noise filter for radio power? Some small wire may have been melted, such as to the ignition coil and starter solenoid.

A dealer did it to me (1965 Sumbeam Imp positive ground) When the generator light came on and got brighter the faster I went, I drove right back. I ended up with a new generator, starter battery and regulator.

::: UPDATE :::

I replaced the alternator tonight which has raised a new issue. After connecting the battery (correctly!) I tried my lights which worked along with the dash oil pressure and alternator warning lights. Everything was fine until I turned the key at which point the car lost all power once again. I disconnected and re-connected the battery and immediately had lights back. My only thought is there is a short in the starter solenoid. anyone have any other suggestions?

You may have reverse-polarized the starter. The starter solenoid may be stuck closed. The starter drive may be jammed in the flywheel ring-gear.
Don’t you have the repair manual (Chilton’s, etc.) as an aid?

It sounds to me that there is a damaged wire or connection somewhere in the main power buss area. I assume that when you connected the battery leads reversely you disconnected them immediately or did you try starting the engine while the leads were reversed?

If you have an external regulator check that. If something isn’t turning on like the lights then start checking for a break in power connection to that area. Work back towards the battery source. Also check the grounding wires to the chassis for signs of heat damage.

I’m guessing there’s a short in the solenoid, it’s the only thing that makes sense. I have power before turning the key, and immediately lose it when I do. It remains that way until the battery is disconnected (freeing the solenoid) and only afterward do I regain power throughout the car. I don’t have a chilton’s but am seriously considering one. Trouble is the car started and ran perfectly before I pulled this rookie mistake, now I’m chasing gremlins.