Video Killed My Radio Star

May 5, 2005 3:13 PM

[AutoRepairFilter] - While jump-starting my car a while back, I placed the jumper cables backwards on the battery, and since then some of the electrical things in the interior of the car don't work.

I have a 98 Ford Contour, and now the Radio, Clock, Interior Lights, and Remote Entry have stopped working. There are two fuse boxes in the car, one under the hood, the other under the dash. The fuses for all of the non-working elements of the car are attached to the fusebox under the dash.

The fuses for the Radio and interior lights (the clock and remote entry aren't listed in my owner's manual) are good. I've replaced them just in case, but they were fine. These fuses are not in sequential order in the fuse box, so it doesn't appear to be a section that is physically near each other. Other interior things light the lighter, dash lights, power windows, power door locks, etc. all work fine.

I hooked a volt meter up to where the fuse plugs in for the radio, and set to auto-range, its shows .62 mA. So it seems like current is getting to the fuse box.

Any clues on where to go from here. I can't afford (time or money) to leave my car at the dealership. Failing insight on how to fix this myself, any recommendations on auto repair places in Austin who do electrical work?

posted by stovenator to travel & transportation (12 comments total)

This advice is not from a certified technician, it could be totally wrong. It's a reasonably educated, but highly speculative guess.

It sounds like what you did was had ground going to the power, and power going to the ground.

Since many grounds are shared, it's possible that you sent too much power through them, and in a fashion that neatly dodged the fuses.

Power locks and such would likely survive because they're solenoids, and quite hardy. The radio is probably fried, and the remote zapper is likely gone because the computer that controls it is probably fried. The lights are probably fine, but are likely wired into a computer or something which is fried.

If this highly speculative diagnosis is correct, you could probably just wire the lights to a different switch, replace the radio, and live without remote entry.
posted by mosch at 3:59 PM on May 5, 2005

Ack, that's not good. Isn't the fuse supposed to prevent that from happening?

Hmm...
posted by stovenator at 4:53 PM on May 5, 2005

Google Groups might help. You may have burned some fuse link wires.
posted by weapons-grade pandemonium at 5:13 PM on May 5, 2005

Ouch. The radio likely has an internal fuse. The RF receiver for the remote locks / alarm may have internal fuses as well.

Unless you are a technician, I doubt these are user serviceable items. I'd recommend replacing them with parts from an auto recycler. In the case of the radio.. you may want to go aftermarket with something that can play MP3's or that has an aux input for an ipod.

It is also possible the RF receiver for the remote control is located in the factory radio, as is the dome light if the vehicle was equipped with a factory alarm. This was the case with my old 1996 Honda Civic.

I'm not familiar with Fords, but it is possible your vehicle contains a fusible link which is a wire designed to act like a fuse by melting. I would try to rule this out before you continue.

Unfortunately, fuses cannot protect sensitive electronics from reversed polarity. Good luck.
posted by vaportrail at 5:16 PM on May 5, 2005

Fuses are mainly there to prevent fires. There are a handful of ways that reversed polarity could kill a piece of electronics, and some of them might not require so much current that they'd blow the fuse before blowing the electronics.

I'd pop each fuse out and test it with the resistance setting of your multimeter. A fuse should probably be less than an ohm. A blown fuse will show infinite resistance. (Do 'em one at a time to make it less likely to mix them up as you put them back in.) Is it possible that there's a master fuse of some kind that has blown? Or maybe a separate fuse built in to (say) the radio that could have blown?
posted by hattifattener at 5:17 PM on May 5, 2005

Your cars fuses are designed to protect against overvoltage through standard paths. If you shoved 14 volts down the ground, your fuses will be fully intact but the less robust bits of electronics will be smoked.
posted by mosch at 6:21 PM on May 5, 2005

Electronics (eg radio, computers as opposed to electrics like lights) don't handle reversed polarity, they die. And reversing the polarity generally won't bother fuses (because they blow if the current is too high, not if the voltage is reversed.

So, sorry, but your electronics most likely need replacing. Though as suggested by mosch you could conceivably rewire things so's to bypass the burned-out electronics, if you were really clever and really persistent, personally I wouldn't want to try.

I'm sorry not to be more helpful, but really think that (unless you know more than you seem to) this is not a do-it-yourself repair. (I'm an engineer.)
posted by anadem at 8:31 PM on May 5, 2005

The thing that interests me is that the dome light doesn't work - it's unlikely to have been effed from reversing polarity. I'd recommend looking for fusible links in or near the engine-comparment fuse box.

For the record, I've hooked 'em up the wrong way a bunch of times (I was cheap and used a red battery cable I had laying around to replace a corroded ground) and have never blown *anything* but a fusible link.
posted by notsnot at 9:13 PM on May 5, 2005

notsnot and hattifattener are on the right track with their suggestions on checking main fuses, all of the relevant ones anyway. They aren't going to be in the "regular" fuse panels inside the car. They're under the hood, most likely in a little black plastic box that you'll have to search for. BE CAREFUL. Sometimes you need a needle-nose pliers to get them out, so either disconnect the battery first, or proceed with extreme diligence if you want to avoid your own personal fireworks display. It'll be obvious if one's blown. *Most* modern vehicles have safeguards in place for reverse-polarity situations, just as this.

If this doesn't cut it, it's time to bring it in.

Good luck!

(many years as an Audi tech in my former life)
posted by peewee at 10:48 PM on May 5, 2005

Yeah, I did something like that once on my '89 Probe and blew some kind of "master fuse." Car worked fine once I replaced it.
posted by kindall at 10:57 PM on May 5, 2005

And IIRC, you'll need not merely needle-nose pliers, but probably a ratchet or a screwdriver. That's a beefy fuse and it's probably attached with a screw of some sort.
posted by kindall at 10:59 PM on May 5, 2005

I did the same thing and blew a fuse in the fuse box under the hood. I believe it was marked as the battery fuse in the owner's manual, but I'm not sure. It didn't look like your typical fuse, it was more of a small box shape. I don't remember how long it was, but it was about a half-inch square. It was very obvious that the fuse was blown once I got it out (scorch marks on the inside of the fuse). I thought I'd killed everything in my car, but it turned out that I just needed a $10 fuse.
posted by hootch at 7:35 AM on May 6, 2005