Reversed connections on battery,, car won't crank

Hi everyone,

Thanks in advance for your help. Here’s my situation:

I have a 1993 toyota sportscar that’s in practically new condition. I’ve had it in winter storage under cover. The battery was dead when I went to start it, so I proceeded to hook up my portable battery jump starter to the battery. In my haste I made a bad mistake and I reversed the connections of the portable jump starter to the battery. I only had it connected incorrectly for about 20 seconds when I noticed by mistake and unhooked the jump starter.

There is a four inch long, 14 gague, fusible link wire that comes off the positive battery terminal and connects to cluster of larger wires about 6 gagues in diameter. Luckily, that fusible link wire burned in half protecting the circuit, and rest of the electrical system.

I have since replaced the fusible link wire, checked all the other fuses that I can either pull out or see from the top and they’re all fine. My battery is brand new , just purchased, and I put it on a trickle charger until it indicated that it was fully charged.

I connected all of wires back up to the battery and tured the key… All of the electrical works such as the radio the headlights the gauge cluster and such.

However, when I try to start it I hear the starter solenoid click and buzz but the car will not crank at all.

Any ideas?

There are a couple fuses and fusible links for the starter on the MR2 if that is the 93 sports car you are talking about.

Thanks. Can you tell me where the starter fuses and fusible links are? the illustration you posted is too small for me to see. Thank you.

You should be able to click on the link and open it full size. As far as where the are, the links should be in the wire frm the battery to the starter. The fuses should be in the fuse box.

You might as well check all the fuses while you are in the box. If you can’t start after a visual check, use a volt-ohm meter (VOM). Be sure to wear rubber gloves when you do this. No, not to protect you. Electricity will be conducted through you though and an open circuit in a blown fuse will appear good. With gloves on you can hold the probes tight to the fuse blades.

You might have gotten lucky and the problem is just the battery is bad or the battery connections need a cleaning. Have you tried using a battery post cleaning tool on the connections? If so, then have you removed the battery and charged it for 24 hours with a battery charger? If you’ve done both of those already, so the connections are clean and the battery is fully charged, then the next step is to take the battery to a shop for a load test.

One more thing. Other posters have done this same thing and a common problem that seems to show up is that an alternator diode gets fried. If you finally are able to start the car ok, but it isn’t recharging the battery correctly when running, suspect the alternator was damaged in the reverse-connection incident.

If you are sure the starter solenoid is functioning then you are down to a few possibilities. A weak battery or faulty connections, the main cable going to the starter is bad (internal wire corrosion), the solenoid contacts are bad, or the engine is locked up. You should see at least 10 volts getting to the starter solenoid contacts while cranking the engine.

Measuring battery voltage while cranking is a good diagnostic. If the volts drop to 10 or so, but the engine doesn’t turn, a bad starter is indicated. If volts stay at 12, juice isn’t getting to the starter motor. Your main starter contacts should be in the starter housing. They are known to fail (been there). Otherwise, back up through the wires to find out where the electrons are being stopped.

In the fuse box under the hood in the frunk (passenger side) you will find a square white fuse with a clear plastic window in it. Look through the window. Is the copper bar intact? I’m guessing not. Time to replace that fuse. That’s the one that usually blows when you reverse your battery.

BTW that fusible link is probably for a stereo and didn’t protect anything but your audio system.

In the fuse box under the hood in the Trunk (passenger side) you will find a square white fuse with a clear plastic window in it. Look through the window. Is the copper bar intact?

Just looking won’t always tell you I had one like that in a Honda looked good but it would only pass current if you pressed on it real hard. Use a meter or test light if you can get at the contacts.

Wooo Hooooo! It started! Wow does it run well. I was so relieved and exited I took it our for a long dive on the freeway! It feels great to be driving it again after a long winters nap. 0 to 60 in bink of an eye. Turbo kicks in It throws me back into th seat. 80, 90, 100 no problem…thats where it loves to reside.

okay, I noticed I had blown two fuses in my stereo amplifier. that got me thinking that perhaps the current made its way to another fusible link somewhere. I located the wiring schematic offline and there is another fusible link from the starter to the starter relay.

I spent all afternoon tracking down wires from the starter to the starter relay. All looked fine. the starter checked out fine as well. I used a fuse tester to test all fuses and they checked out fine. I took the battery over to the parts store and had it tested. It tested out completely fine.

So I got to thinking that maybe the splice I had made with the new fusible link wire off the main battery terminal to the larger cluster of wires wasn’t producing a good connection. So I took that splice apart and redid it tightly with a copper butt connector and electrical shrink tubing insulation. All nice and professionally done. Put new fuses back in my amplifier. Turned the key and it started up to a wonderful roar! The beast is alive and wanted out of its cage!

Hey thanks everyone for your encouragement and help. It made me feel like I wasn’t going through this ordeal alone and that’s the most important point. your advice helped me to learn more about automobile repair, and my car that I didn’t know before.


@PvtPublic Quite true, although usually when you reverse the leads like that, the fuse blows and you can see the broken link and the scorch marks.

BTW, on the MR2 the front trunk is called a frunk, to distinguish it from the conventional trunk behind the engine - wasn’t a typo, the MR2 is just an oddball :wink:

@TCC Glad you got it fixed. You should post a pic or two of your ride - MR2’s are cool cars that we don’t see much anymore (and I own one so I’m biased :wink: )

Glad you got it going again. One of the best investments you can make in your vehicle is getting a factory service manual, at least for the wiring portion. It will show you all the wiring details and where to locate them in the car. Ebay is a good source to find them at a good price. Another thing to have in your tool box is a test light probe to check for power. Even better is a digital multimeter. Without those things a lot of time is usually wasted in finding troubles like this.