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Help diagnose my electrical problem?

My '04 Mustang died abruptly and I’m trying to figure out what happened. Any advice would be much appreciated!

I’ve owned the car for a little over a month and it’s been running just fine – starts right up, no issues that I have noticed. I’ve taken it into the shop twice for maintenance and it’s been given a glowing bill of health.

The morning the car died, I had driven to the supermarket and back with no problems at all. Parked, ran into the house, came back, started up the car – nothing. Totally dead. No dash lights, no crank. Power locks/windows inoperable. Could not unlock or lock the car with the key fob.

Tried jump starting. First attempt, used the kind of cables that hook up between the cigarette lighter ports of the two cars. With the cars connected, when I turned the key to the ACC position the dash/interior lights came on, and when I tried to start there was a rapid ack-ack-ack-ack sound which I am guessing is the starter. Waited a few minutes and tried again – this time when I turned the key on everything just went completely dead.

I tried again, this time with regular battery-to-battery jumper cables. The first time I started up, the dash/interior lights came on with the key in the ACC position, but when I tried to start, there was just a brief sound like a cough, then everything died.

Tried to start again – this time, no response at all.

Thinking the battery was dead, I went and bought a brand new battery and swapped it out. Started up - nothing.

Attached jumper cables again, and the same thing happened as the first jump attempt above.

Hours later, I tried starting the car again to see what would happen, and again, the dash/interior lights came on, but when I turn the key, the same coughing sound and then everything goes dead. Repeating the process – no response at all.

I’m unfamiliar with how automobile electrical systems work, so I’m not sure what part (or parts) is at fault here. I’ve been told that the alternator is not a likely culprit, since the car should have started up with the jump. The advice I’ve received to date has mostly pointed to a connection problem from the battery – probably corroded cable connectors.

I checked the positive/negative cables, and they do look corroded. It looks like some maintenance has been done previously on the cables, since the negative connector is different and newer than the positive. On the negative cable, the insulation stops about a half inch before the connector, and the bare wiring is covered with white residue.

My question is, are the symptoms I’m experiencing consistent with a corroded ground or positive battery cable? Is it a common thing for a corroded cable to just abruptly lose connection like that? It is true that I had handled the negative cable a couple of times in the past few weeks, disconnecting it in order to install first an aftermarket stereo receiver, and later on a fuel filter, so I can see how that could have exacerbated whatever’s happening with the cable.

If the problem is the cables, would it be expected that the car would go completely dead and then, later on, appear to have enough power to bring back the interior lights (but not enough to start the car)?

Alternatively, is there a more likely culprit here than the cables, like the starter/solenoid? If so, why?

Sorry for the long post…this is making me pretty anxious as I’m dreading an expensive repair. Any help would be much appreciated!

Since everything went fully dead immediately, I’d agree with the focus on the cables and connections. I’d get everything cleaned up or replaced there before doing anything else. I’ve heard that corrosion can get up under the insulation, so check there too.

The quick answer here is you do have a power connection problem with the battery cables, not a bad battery or alternator. Many a car owner has paid the price for not taking care of one of the most simple maintenance items on a car…the battery connections.

Corrosion can happen internally to the wiring at the battery clamps and so you can’t see it normally. You saw the ground cable though. Perhaps someone removed the insulation looking for corrosion. You should at least replace the ground cable and it might be wise to replace the positive wire also. Factory replacement wires are usually the best to get. There is another smaller wire on the positive side that ties power to the electrical panel under the hood which supplies power to the whole car except the starter motor. Make sure power is getting to those fuses while trying to start the car. At the least, invest in a test light probe so you can check for power.

You may have blown the fuse on the cigarette lighter due to the high current draw. Trying to jump start an engine using that socket is bad idea.

I’ll add step 2 and 3 to the cable checks suggested above. If you can get to the starter electrical connections (the big red wire going to the starter), use your jumper cable from the - (or black) battery terminal and clamp the other end on a bare metal point somewhere on the engine. From the + (or red) terminal on the battery clamp your other jumper and touch the other end to where the big red wire attaches to the starter. If the starter spins, one or other of your battery cables need to be replaced. You can determine which by unhooking the black jumper from the battery and see if the starter still spins. If the starter doesn’t spin, you may get a big spark but the starter is bad.

Many thanks for your advice! I guess I’ll start with testing the connections and will go ahead and replace the connectors for good measure. I’m really hoping not to have to replace the cables entirely, since for some reason in this Mustang the wiring looks dauntingly complex, and it doesn’t appear I can use the standard auto parts store cables but would have to order some fairly pricey cables compatible with this car. (I may be wrong about this, but the Mustang cables seem to have some extra wires linked to them, and I’m just not handy enough to modify the store-bought cables or build my own as many do.)

Try cleaning the connections using a small wire brush as a first step. If that doesn’t fix things then I suggest you use a test light to try to find the bad connection before replacing anything.

If the one battery terminal looks different than stock probably one that you would use for a replacement has white reside on it, that may be your problem. I have an 89 GT and one day went home for lunch and same thing happened…I think they are 7/16 or 1/2 inch bolts. Loosen the bolts and clean everything. The battery wires and the battery connector.

With a new battery and the starter chatter this does point to more than likely a bad cable connection. If not at the battery, then maybe the ground connections at the end of the positive cables. A faulty starter motor could also be a possibility but the odds of that are very slim and I don’t think the starter is the issue.
Battery cables used to be pretty simple items but they’ve become pretty convoluted on modern cars.

A total lack of electrics on the chassis (excluding the starter) could point to a failed or failing high current fuse in the underhood box. (Next to the battery and has 30.40, 50 amp fuses, etc)

If it’s any encouragement, keep in mind that most electrical issues are comparatively simple in nature. It’s easy for even an experienced mechanic to overthink things, assume the worst, and start at the end of the chapter instead of the beginning…
Heads up, it will work out. :slight_smile:

Quick update just to close out my topic. Yup, it was the corrosion on the connector(s) and cable wires. I believe it was the negative cable that was the culprit (although the positive connector was badly corroded, so I went ahead and replaced both). It had obviously been replaced in the past, and whoever did it failed to cover the bare wires in any way, so there was a shower of crap that fell out from it every time I so much as tapped it. When I took off the connector, it was clear that the wires were badly caked with gunk. I cut back the cable and put on the new connector, started up and hallelujah, she’s alive!

Thanks again guys for your help!

There are sealers you can apply to the connectors that will keep the corrosion from forming again on the new connectors. Thanks for the update.

A $1 jar of petroleum jelly from the Dollar Tree will protect the cables just fine.

I put the .99 felt rings on the battery posts. They neutralize the out gassing around the posts and keep the connections from corroding.