# Idiot Friend Jumped my Truck Backwards... HELP!



## 86HARD (Aug 18, 2014)

I have an 86 hardbody with V6 5-speed (VG30i) I believe. I'm by no means a Nissan expert. A friend borrowed my truck, let the battery die and then jumped it with the terminals backward. Ever since, it will crank but not fire. I have checked and there is no spark. Any Ideas? Checked fuses, checked relays on passenger fender... any thing else obvious?


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## SPEEDO (Jun 9, 2003)

did you check the fusible links?? hopefully thats all that fried...


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## jp2code (Jun 2, 2011)

If the fusible links did not burn out, then your ECM under the passenger's seat likely got fried.


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## SPEEDO (Jun 9, 2003)

^ +1, thats what I am afraid of...


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## 86HARD (Aug 18, 2014)

Thank you guys for the replys! I'm new to the forum and new to wrenching on the old Nissan. Stupid question, what is a "fusible link"? Where do I locate and how would I test? Again, new to the Nissan but fairly mechanically capable.


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## jp2code (Jun 2, 2011)

86HARD said:


> Thank you guys for the replys! I'm new to the forum and new to wrenching on the old Nissan. Stupid question, what is a "fusible link"? Where do I locate and how would I test? Again, new to the Nissan but fairly mechanically capable.


Looking at the POSITIVE (+) terminal on the battery, there should be one big fat cable going to the starter and 3 or 4 smaller wires coming off with it.

Those 3 or 4 smaller wires are fusible links - meaning, they burn into when too many amps go through, instead of frying the electronics in your truck.










You can disconnect them from the battery and Ohm each wire out, but if there is a small burnt part, you could complete the circuit when you move the wires around. Also, disconnecting them is going to zero all of the radio stations on your stereo and make your clock blink 12:00.

Fusible links are not expensive, and they are sold at the Nissan Dealership.

Safe bet is to buy a couple from them - one to replace the old, corroded one on your truck now and one to keep on-hand.

Here they are on Courtesy Parts for under $10:

WIRE-FUSIBLE LINK - Truck (D21) 11/1985-08/1986 Z24 & VG30 BLACK :: Nissan Parts, NISMO and Nissan Accessories - Courtesyparts.com

Your local dealer has to factor in shipping costs, so figure around $15.


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## 86HARD (Aug 18, 2014)

jp2code - Thank you so much for the info! I really hope this works. I love this old truck and really want to get it back on the road. As you seem to be quite knowledgable, I have another electrical question for you. I had the truck in AZ with me while working and the little plastic grommit behind the brake pedal shattered. My battery died from my brake lights being on and ever since, I have to have my lights turned on for my radio to have power. Also, the truck burns out headlights much faster than normal. In some cases as little as one day. Any of this sound lile a familiar issue you've heard of or just a typical electrical gremlin? Loose ground, burned wire, corroded terminal etc...


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## jp2code (Jun 2, 2011)

Is this site loading up slow for anyone else today, or is it just me?

Do you have the 1989 version below?










This forum won't let me post the link to that site (it is blocked) so I have to use a picture.

Download that PDF and save it to your My Documents folder. It can tell you how to fix everything on your truck!

After you get it downloaded, go to the Electrical section, EL, which covers all of this.

 EL-6 - gives an overview of the wiring from the fuse box.
 EL-40 - Headlamps
 EL-43 - Exterior Lamps (Rear Brakes)
 EL-78 - Audio (Radio issues)
The first thing you want to realize is that each of these components (Headlamps, Exterior Lamps, and Audio) are all plugged into different areas on the fuse panel.

If turning one of these items on results in another item being turned on, then you may want to verify that they are all still connected to the correct fuse panel locations.

For example, try pulling the fuses out for Exterior Lamps and verify that the brake lights do not work.

The headlights are each on separate fuses. If one of those fuses are bad, then one of your headlights won't work but you will not be left in the dark on your ride home.

It could be that one of the previous owners of your truck took the least effort possible in fixing something, which resulted in wires being routed the wrong way.

If you can confirm that the fuse panel goes to the correct assemblies, then you have a grounding. Those can be very hard to find, because it could simply be a cable that is pinched somewhere on the truck, allowing current to flow through it.

On the Brake Lights, do you have an aftermarket trailer hitch wired up? Those kits often use "crimp connections" that work fine when they are first installed, but would corrode after 20 years of use. If you have one, peel the electrical tape off of the connections, snip the nasty wiring off, strip a clean section of wire, and re-crimp each one.


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## SPEEDO (Jun 9, 2003)

fusible links, you should have one with a grn/blk wires and one with pale redish/brownish 3 wire.. (as jp said + side cable) did you get the little plug fixed?? when mine went out I taped a penny over the hole until I could get one, might also check the h/lmp switch, clean contacts if needed


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## 86HARD (Aug 18, 2014)

SPEEDO & jp2code - Thank you both for all your help. I looked at the fusible links when I got home and it appears I have two. One is a single black wire and the other has two geen and two red wires. One of the green wires had a large "blow out" in the outer sheath and when I cut in open, the copper wire was broken and no longer touching. I am really hoping this is my issue but I can't get a replacement until tomorrow at the earliest. I'll let you guys know if this was the fix and if so THANK YOU BOTH!


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## SPEEDO (Jun 9, 2003)

fingers are crossed...


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## 86HARD (Aug 18, 2014)

SPEEDO & JP2CODE,

Finally got my hands on both of the fusible links from my local Nissan dealer and... no luck. Trucks just cranks. I pulled a plug and still no spark. I had my wife stick her head under the seat to see if she could see lights on the ECM but she didn't see any. I wasn't sure where they would be anyway.

Any ideas on next steps? I'm guessing I need to pull out the computer and see if there is life? How can I check it?

Thank you guys so much for your knowledge and help with this!


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## jp2code (Jun 2, 2011)

Does this video help?

https://www.youtube.com/watch?v=6l7SwU7ZuVk


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## 86HARD (Aug 18, 2014)

That will help. Looks like it's time to pull out the seat and get after it!


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## jp2code (Jun 2, 2011)

Mine is a 1994. Since yours is a 1986, you will have a toggle switch instead of a knob to turn like my truck has.

Otherwise, it should be the same.


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## 86HARD (Aug 18, 2014)

Awesome, thanks again. Just curious though, if it is the ECU, do you know how much they are to replace? I had to replace one in my wife's old Civic a few years back which wasn't too expensive but the one in my new Jeep failed right after I got it. Warranty item but it would have been like $2,200 to replace. I'm hoping an old Nissan isn't that much?!


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## jp2code (Jun 2, 2011)

The ECU generally runs $100-$200 on eBay.

Finding an exact match is harder, and I'm not sure exactly what years are interchangeable.

Here's an eBay search for ya:

1986 nissan d21 computer | eBay


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## 86HARD (Aug 18, 2014)

Sweet, I was hoping it would only be a couple hundred. Is there an easy way to check to make sure power is getting to the ECU? I want to make sure that the lack of lights is becuase the ECU is fried not just becuase there is an issue upstream with power. I assume I can just check for voltage with a multi-meter but I'm not sure which connection to check.


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## jp2code (Jun 2, 2011)

There is ECU testing information in the EF & EC section of the Service Manual. (link up in Post #8)


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## 86HARD (Aug 18, 2014)

I couldn't the PDF's to open. I tried opening on the web, saving to my desktop as a PDF, tried opening with Adobe and Bluebeam but it just came up blank.


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## jp2code (Jun 2, 2011)

Are you on a smartphone?

On a Windows PC, you could Right-Click a link, select "Save As...", and put it in your My Documents folder.


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## 86HARD (Aug 18, 2014)

SPEEDO & jp2code. I know it's been a long time but it's finally been resolved! She lives. Unfortunately, you were correct, while it did pop the fusible link it also fried my ECU. I waited and waited till I found the correct one from a junk yard (didn't want to pay Nissan $900 for a new one). Finally got one that will work in an 86', V6, MT, 2WD, SRW. Now I'm chasing some kind of ground, lose wire issue with the electrical system but that's ok as long as she runs! One more question though is what is the truck worth? It's got 220K miles, standard cab, long bed and in pretty good shape overall. I've just got no clue what it's worth.

Thanks again for all your help.


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## jp2code (Jun 2, 2011)

I've seen these sell for as little as $1500-$2000, but I would never sell one for that little.

The Cash-For-Clunkers campaign saw a lot of these old trucks get scrapped, so people who are interested in them are stuck paying more money for them.

I'd say $4000 is the lowest I'd sell one for because most new car dealers will give that as a trade in on a new vehicle.


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## 86HARD (Aug 18, 2014)

Wow, I'm suprised by those numbers. I was also suprised by the fact that I couldn't find ANY for sale in my area. Even on Ebay or Autotrader, they just aren't out there for sale. I know it's just a little pick up but with that long bed, it's super useful. And has plenty of tourqe.

One other general question since you know so much about these trucks, should the gearing be super low? I'm wondering if somewhere in the last 30 years, someone replaced the rear end or rear end gears becuase you can literally start in 3rd or 4th gear on flat ground easily. I'm in 5th gear by 30 mph. Is it normal with the V6 5spd to have such low gearing?


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## jp2code (Jun 2, 2011)

Yeah, sounds like you have one like mine.

The tag on your door probably lists the axle as an HG46. HG is limited slip (HF is not). 46 is 4.6:1 rear gears.

That's what I have, anyway. 5th gear at 30 MPH is normal. 55 MPH at 3000 RPM, too.


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## 86HARD (Aug 18, 2014)

4.6:1, that is crazy. Doesn't seem necessary for that truck. Thanks!


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## 86HARD (Aug 18, 2014)

jp2code said:


> There is ECU testing information in the EF & EC section of the Service Manual. (link up in Post #8)


jp2code - I thought I had all of the bugs worked out but still have an issue. When I replaced the ECU, I knew the battery in the truck was bad so I just pulled the neg. connector off the battery when the truck was sitting. This isn't a daily driven truck and can sit for weeks at a time. I finally went and bought a new battery but was very annoyed when it sat for a week and was completely dead. Less than 2 volts left. 

After pulling out my multi meter and routing around through everything, I isolated that the new ECU I put in is the source of my power draw. The ECU is from an 86 and like you said, it has the Toggle on the back that reads either "On" or "Off". It doesn't have a "Diagnostic" designation like some threads I have seen. In the "Off" position, both the red and green lights remain on at all times except when the truck is running. If the ignition is on, they stay on but as soon as I start the truck and the ignition returns to the on position, they turn off. If I put the toggle in the "On" position, I get a 13 code that just reapeats over and over no matter if the key is or not, ignition is on or off or truck is running.

I'm a total loss as to what to do next? Any ideas? I'm about to just install a toggle switch in the power wire leading to the ECU so that I can shut it down each time I park the truck. Thanks again for all your help. You seem to have actual knowledge about what you speak not just the normal "forum B.S." that you sometimes get on these.


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## jp2code (Jun 2, 2011)

You've got to get yourself one of these and keep it on the dash of the truck:

Amazon.com: Schumacher SP-200 2.4W Solar Battery Maintainer: Automotive

2V typically means that new battery is dead beyond recharging, but you could get lucky.

I believe that toggle switch on your ECU is, in fact, what you would use to read the codes. That year ECU does not have different modes like the newer ones with the dial switches, though. Instead, you just turn it on and read the codes. The newer ones have a mode to read the Air/Fuel mixture (nothing on how to set it, though) and another mode to test functions of various switches (like throttle position switch and such). Still, reading the codes is all most owners use it for, which is in Mode 3.

> In the "Off" position, both the red and green lights remain on at all times except when the truck is running.

OK, that is not good. It sounds like something else is wired into the electrical harness. I'm not sure where exactly the ECU gets its power from, but it should be OFF when the Ignition is OFF.

Most likely, someone added an accessory to the truck at some point in its life (common culprits are a radio, amplifier, fog lights, trailer lights, or an alarm system). When this was wired up, someone routed a wire the wrong way and sent power to the ECU.

Do you have any added accessories that remain ON when the ignition is turned OFF? If so, look real close at how it is connected to POWER and to GROUND.

If not, then I would guess your ECU may have a cut in the wiring harness that either allows power to get in or the wires to come into contact with GROUND.

Most of the electrical on the Nissan vehicles have power applied to them all the time (lights, horn, cigarette lighter, etc.). Turning them "ON" actually only switches the return line from those devices to GROUND so the circuit can be completed.

So, if you had a pinched ECU wiring harness that caused the ECU's power to come into contact with the Bench Seat bracket (as an example), then you would have a short that is hard to diagnose.

I appreciate the compliment, but I wished I could be more help with things like this.


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## 86HARD (Aug 18, 2014)

I know it's almost impossible to diagnose this stuff on line just based on someones description. Especially electrical. My truck has trailer lighting harnes that is tied into the left rear break light. This has been there for the 15+ years I've owned the truck and never had problems. I checked the wire and connections for any breaks for worn wires and it looks good. The radio is also aftermarket but has been there as long as the trailer harness. The radio does not stay on when the key is off and the power is coming from the black power with the wierd plug. It's not tied into some butchered harness. Now that I have the truck back up and running, i've been doing some other things and think I may have a lighting issue. 

Before I replaced the ECU, I had a problem with a dead battery and when I got it replaced, I had to turn the light switch on to (running lights OR headlights) in order for the power to go to the radio. After replacing the ECU, I also pulled all of the switches off the steering column and cleaned the contacts and WD-40'd it all to clean it. This seemed to help the radio problem but now... I get the quick blink when I use the left blinker but the bulb is not out. The lights in the bumper both work in running light mode but only the right side blinks as a blinker or when using the hazards. Both rear's are working perfectly. In addition, my orange running/blinkers that are next to my headlights are both not working. I put in new bulbs but nothing. Should I replace the light switch? I've heard these things can cause all kinds of problems.

The radio and trailer harness are the only non-factory things on the truck but neither is drawing power when the ignition is off. When I disconnect the Block that plugs into the ECU which provides power, the draw on the battery instantly stops. 

So, because the red & green lights remain on when the truck is off this sounds like my problem source. I'll try to trace out the harness issues.


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