Help Needed with Wiring/Finding Short

[medusa3000]

Hello folks, tried looking through the existing help threads and finding some resources/diagrams on here (and elsewhere) but any help would be much appreciated. Disclaimer: I know close to zero about engines/automotive repair, especially electronics and wiring so pardon the lack of knowledge.

The long and short of it is that I fried both the ground wire to the battery and the ground wire to the engine when I was attempting to replace my battery over the weekend, bad battery is what I'm sure was causing my no-start issue (cranking, no ignition). Tested the battery that was in there (3 years old I put that one in myself), multimeter read 12.3V. Checked for spark and fuel pressure for good measure and was getting both. New air filter as of September and intake seems fine. Fuses and relay are all good. Took the old battery to AutoZone for a load test and turned out the battery was in fact bad, bought a new battery. Took the terminals off, cleaned them with lemon oil, then applied some of that anti-corrosion goo.

After I tried to put the terminals back on the new battery is when the spark from the negative terminal fried the wires.

At this point I'm pretty lost on where to go with it considering I never had any indication of a wiring issue in the 4 years I've had this truck. Even with my limited understanding it just seems bizarre that both wires would fry. So, any resources/videos/advice would be greatly appreciated. :bounce:

Two wires that got fried:

Pos and neg terminals:

And here's one of the engine ground. Looks as if it is improperly ground (on paint):

Thanks in advance

 

[T.Tech]

If all you switched was the battery and this happened, is there any possibility that they gave you the wrong battery with the terminals reversed? I’ve never seen that happening by just the spark of hooking up the battery, it takes a lot of current for the insulation on those thicker gauge wired to melt.

 

[dogtail]

Yeah really sounds like positive and negative terminals/cables got reversed.

 

[jgue467]

Yup reversed wires are about the only thing to cause this or another bad battery with polarity reversed in one or more cells. I mean to get so burned the cables were kept on reversed a long time, usually it's a quick spark-pop to let you know and you pull away ending that mess.

Did you experience this as you put the 2nd cable onto the battery? When I've done this by accident, the sparking-popping doesn't give you any time to want to clamp down the cable. You immediately know it's wrong.

What happened in your case when the 2nd cable was installed onto the battery?
Nothing, sparking, what? :cowboy:

 

[TheDurk]

Yeah really sounds like positive and negative terminals/cables got reversed.

I've never done it, but I have seen victims of that particular mistake, and just reversing polarity doesn't do that either. It will fry relays, blow fuses, melt your alternator regulator, but I have not seen it do THAT. THAT happens by a direct unfused full-load short, which is not easy to do. Nothing in the story really tells me why this would have happened. I would think the ground cable was attached first, or removed last (rookie mistake) and then the mounting bracket or some other robust ground contacted the positive terminal. And that, boys and girls, is why you remove the ground first, and attach it last.

I think I would just assume all major cables are compromised, and do a full 'Big Three' upgrade, recognizing there might be more to do after I did that. My guess is the fault was momentary during removal or installation, and that is all that will be required.

http://www.toyota-4runner.org/3rd-gen-t4rs/139597-performing-big-3-wiring-ugrade-3rd-gen-toyota-4runner-how.html#post1351137

I have no experience, thankfully, with a sustained reverse polarity installation. So I guess that damage is possible from that, presumably through the alt. but I don't quite understand how. The 100A Alt fuse usually blows, protecting the cables. I really think this was an unfused short.

 

[Kanoe]

There is something not right about those battery terminals (beside the fact that they are really crazily done).

Take a look at the negative. That piddly little solo wire looks like the fender side tie and where is the heavy starter negative??

It's right there in the middle of the positive terminal. In stock configuration there should only be the left one (starter) and right one (main fuse box supply). What the hell is the black one in the middle?

I think the OP opened up those screw clamps and put the starter negative cable back in the wrong post. Dead short from starter to engine to frame and poof! That's my theory.

Op, you can go to a Nissan dealership and get the OEM positive clamp for $10 that is identical to the one your truck left the lot with. It's more expensive at the Toyota dealership. It's a lot better than what you have there. The negative is harder to fix as it is a pre built harness, but it looks like you need to replace it anyway.

Oh, and the engine ground on the firewall is the way they all are, unless of course yours burnt up also.

 

[TheDurk]

There is something not right about those battery terminals (beside the fact that they are really crazily done).

Take a look at the negative. That piddly little solo wire looks like the fender side tie and where is the heavy starter negative??

It's right there in the middle of the positive terminal. In stock configuration there should only be the left one (starter) and right one (main fuse box supply). What the hell is the black one in the middle?

I think the OP opened up those screw clamps and put the starter negative cable back in the wrong post. Dead short from starter to engine to frame and poof! That's my theory.

Op, you can go to a Nissan dealership and get the OEM positive clamp for $10 that is identical to the one your truck left the lot with. It's more expensive at the Toyota dealership. It's a lot better than what you have there. The negative is harder to fix as it is a pre built harness, but it looks like you need to replace it anyway.

Oh, and the engine ground on the firewall is the way they all are, unless of course yours burnt up also.

This would fit my analysis, too. Big-time unfused direct short. The crappy terminals is why I suggested a 'Big Three' upgrade to start over with it all renewed. TheDurk is not a fan of cheapo bolt-on terminals.

The good news is there is less to fix with a direct short than with a reversed polarity fault. Fix the short, repair the cables and you're done. The reverse messes up lots of things, some of which may be hard to find.

 

[gamefreakgc]

Yup, you discharged probably the entire battery's worth of power all at once. Should just be able to follow the fried wire until it's no longer fried, and just upstream of that should be your short.

 

[medusa3000]

Thanks for the all the responses friends. I think Kanoe hit it on the head, and now I need to hit myself on the head! :doh: I should've taken a closer look at how I rewired my terminals. Moving the starter negative cable into the positive terminal when I reinstalled the clamps... what a dumb mistake! I'll check the battery one more time and make sure its good to go but I doubt there's anything going on there, and double check all the fuses.

I think I'll go with the Big Three upgrade like TheDurk suggested and cross my fingers that nothing else got fried. Valuable lesson learned here and now I have to pay the price. Appreciate all the help, will keep this thread updated with the repair.

 

[dogtail]

Good that you found the issue, btw your new forum name is "Sparky"

 

[medusa3000]

Update: Success! Well, sort of.

The good news is that I yanked the burnt wires, got new wires, wired everything back up, reconnected the battery, and voila! No spark, lights are on, engine is cranking!

The bad news is that unfortunately that didn't solve all of my problems, and I'm right back to where I was. Cranking no-start.

I decided to skip the Big Three upgrade on this one, and went with a very standard replacement instead. I wasn't feeling confident enough with my skills underneath the hood, and as much as I love my 3rd gen I'm not planning on doing a whole lot of mods to to it. What I did decide to do was to get completely new negative cable (both negative to block and negative to body) and take out. This one has both of the cables crimped and wrapped to the clamp so there is absolutely no way I can make the same mistake again. Sorry for the disappointment Durk.

At this point I don't really know where to go. Now when I crank, it sounds like it sounds like the crank is dropping out after 5 turns for a weak 6th turn before going back. Isn't the crank supposed to be consistent? I haven't checked the big fuses/relays so I'll start there and make sure the short didn't fry those. I'm not getting any RPM when I crank but I don't know if that matters or not. Any ideas?

Good that you found the issue, btw your new forum name is "Sparky"

I'm perfectly okay with that. Not the first time I've fried circuits.