# Lighting Issue... YAY!!



## 86HARD (Aug 18, 2014)

I'm no mechanic but mechanically inclined enough for most maintenance and repair issues, however, my wife was driving my 86 D21 and decided to adjust the brightness of the dash lights. For some reason when she turned the rheostat, the drive lights and head lights stopped working. I checked the obvious stuff, noticed the "clearance illumination" 10A fuse was blown. Replaced it and as soon as you turn the headlight switch, it blows again. Replaced the rheostat (dimmer switch) replaced the column mounted light/blinker switch... no joy. Of course, my truck had a trailer wiring harness butchered into the rear harness which I have since removed. I also repaired (using solder) the rear harness at the affected areas.

Does anyone have any advice on what to do next? I'm at a loss as to why adjust the dash lighting dimmer switch could have affected everything this way. I understand that the lighting switches are all tied via one power source but other than that... I'm lost.

Brake lights and blinkers work fine.

Thank you!


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## SPEEDO (Jun 9, 2003)

have you checked the fusible links, h/lmp relays ? loose connections? etc


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## 86HARD (Aug 18, 2014)

SPEEDO - Always coming to help!

I replaced the fusible links that are connected to the battery when I discovered that they were blown about two years ago when a "friend" jumped it backwards. I did a visual inspection when I was searching for loose/frayed wires this weekend and didn't see any signs on the outside of the coverings. Are there other fusible links that are specific to the lights somewhere else? Should the clearance light issue be affecting the headlights? I think the headlight issue may be due to an overload that actually blew the headlights. After I pulled the trailer harness last night I was out of 10A fuses so I put in a 20A and the clearance lights worked for a couple seconds but the headlights did not. I'm guessing the actual bulbs blew in the headlights.

Can you help direct me to the head lamp relays and fusible link(s)? Also, in reading some other posts, it sounds like the rear tail light housings are prone to failure and that can cause similar issues...?? What I don't understand is why the rheostat that controls the dash lights would have caused this? 

As always, thank you very much for the help SPEEDO.


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## jp2code (Jun 2, 2011)

The wire going to the ILLUMINATION CONTROL RHEOSTAT has power on it anytime the vehicle is turned on.

That wire feeds to a lot of different places. If any of those spots has a short to ground, you would be tripping your fuse.

I would recommend against putting a 20 AMP fuse in your 10 AMP slot. All that can do is send too much current to electrical components that can't handle the load.

Here is a schematic from the 1994 service manual. I don't know how similar that would be to the 1986 wiring.


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## 86HARD (Aug 18, 2014)

jp2code - just like SPEEDO, you always reply and try to help which I greatly appreciate.

I only put the 20A fuse temporarily to see if my trailer harness removal fixed the issue. I would not leave it in permanently.

After reading the numerous threads regarding similar wiring issues, it seems that if it's not the switch (I've replaced mine) it's often one of the rear light housing sockets. I removed the tail lights last night and found that the passenger side lowest clearance light (reverse I believe) is severely corroded. I was able to remove the bulb and it was extremely rusty. Still intact filament but the socket was so corroded it was almost brittle. Also, it appeared that the plastic housing that surrounds the black (ground I assume) wire for this socket had been getting hot and was black. I tried some sand paper and filled it with di-electric grease hoping just to be able to confirm it was the issue but it didn't work. Still popped a 10A fuse. If replacing the socket proves not to help, can you give me any other recommendations??? I know SPEEDO said to check the fusible links, which I recently replaced, but I want to make sure there isn't a fusible link or relay somewhere else specific to the lights that I'm not aware of? Also, this issue caused my headlights bulbs to pop. I thought it had somehow affected the power to them but it actually sent a surge that blew them.

Thanks again for the help.


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## jp2code (Jun 2, 2011)

If you leave the bulb out of that one crusty socket, can you get everything working (except that one backup light)?

If so, hobble along like that until these cheap replacements come in:

Left Side: Rear Taillight Taillamp Brake Light Driver Side Left LH for 86 97 D21 Pickup | eBay
Right Side: Rear Taillight Taillamp Brake Light Passenger Side Right RH for 86 97 D21 Pickup | eBay

Of course, they also sell kits if you wanted to go something full of sparkle.


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## 86HARD (Aug 18, 2014)

Thanks for the links. I haven't tried it without the bulb in it. I will try tonight and see if that works. Either way, I'll update once I figure it out.

Thanks again!


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## 86HARD (Aug 18, 2014)

Well, after two full days of exploration and part replacement, still couldn't find the issue. I tried Chilton, Haynes and other wiring diagram I could find on the web but none match my truck. All the wire designation colors are different. It's like my truck is a combination of an 85' 720 and an 87' D21. I'm pretty sure it's a short or loose ground. I replaced the light switch, again. Replaced all of the corroded bulb sockets and double checked to make sure the bulbs are correct. I used a circuit tester to check every wire from the light switch to each corner's corresponding light and couldn't find any that had incomplete circuits. I re-soldered the wires that I had re-connected after removing the trailer harness. I checked every ground and relay I could find. Still no joy. So, I just ran a 12 gauge wire with an in line 10A fuse from the battery to the front and rear clearance lights. It may not be a fix but at least it's a solution and the truck is now legal. 

Thanks again everyone for the help!


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## jp2code (Jun 2, 2011)

I don't know if you plan to keep fooling with it or not.

Did you try taking one side out? The whole taillight assembly bolts in place from inside the bed, and then you can disconnect it.

If you disconnect one side and the fuse does not blow, there is a wiring issue with the side you just removed. If the fuse does still blow, reconnect it and disconnect the other side.

At least that way you know what side of the wiring is causing you troubles. The wiring harness from the back of the truck to each taillight is pretty small, so there wouldn't be as much to troubleshoot.

If the fuse blows no matter which taillight is out, then you know the short is not in the taillight wiring harness but rather between that junction and your fuse box.


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## SPEEDO (Jun 9, 2003)

feel the fusible links for sold wire, just to make sure its in one piece, the later hb's had a issue with the tlmp harness/sockets, (I have a 86.5 also and mine have been fine) have you checked the h/lmp switch? any burned spots? when people splice in trailer lights they usually make life difficult..


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## 86HARD (Aug 18, 2014)

I replaced the head light switch with one from pick'n'pull and then again with a new aftermarket replacement. I checked all the fusible links with a multi-meter and all have 13+ volts at the wire harness side of each connector. I replaced the tail lamp light bulb sockets and harness connectors. All the wires that I cut were then soldered back together, tested for continuity, covered with heat shrink and wrapped with a plastic wire loom and tested again for continuity. The trailer harness was installed over 15 years ago using "chock block" connecters so they didn't actually cut any of the wires. I cut out the sections that had the sheaths penetrated and soldered them back together.

I tried every combination of tail lamps disconnected, one side connected, all drive lights disconnected, front right & rear left connected etc... and each time the 10A clearance light fuse would pop the second the light switch was turned on.

I tested each wire for the rear light harness that runs down the passenger side of the truck and each had continuity to the original connectors. The Brake lights and turn signals never stopped working so my focus was the pink wire with the blue stripe and red dot that on my truck, runs to each corner for the drive lights. This wire enters the light switch, runs to the rheostat dimmer switch, then to the instrument cluster, then heater & radio and then out to the tail lights. I assumed this has to be the wire with the issue even though I could not find fault in it anywhere I tested.

I'm really thinking it may be a frayed wire somewhere deep in the harness and short of pulling it all out, I have no idea how to find it. 

Another piece of information I just got last night from my dad who gave me the truck is that it's a crate VG30E that was installed about 10 years ago and not the factory motor. I'm sure there was some electrical "work" to make that happen and maybe I'm now paying for it?

As always, thank you both very much.


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## jp2code (Jun 2, 2011)

If the fuse is blowing when no lights are connected, then the wiring in the harness is not the problem.

The wire from the fuse box has 10 Amps on it. That wire goes to your headlight switch on the steering column and then out to the actual lights (there may be a relay involved somewhere).

Anywhere that power is shorted to ground would cause your fuse to blow.

Have you checked the resistance between the terminals of your 10 Amp fuse? It sounds like it goes to zero (0) Ohms as soon as you flip the light switch on.

Old Hardbody trucks sometimes have that light switch go out, too. Replacements are abundant on eBay, and cheap.

$35, shipped to your door:

Turn Signal Switch Beck Arnley 201 1869 Fits 86 93 Nissan D21 | eBay

*EDIT:* How about $28.50?

http://www.ebay.com/itm/271702993009


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## 86HARD (Aug 18, 2014)

I have replaced the switch. That was the very first thing I did. First with a used one from pick'n'pull and then with a new one. Even with the new switch, and every combination of no lights, one light, two lights etc... connected, the fuse still blew. 

To add another layer of complexity, that may help someone with more knowledge than me, when the original issue happened, it blew the headlights. I replaced them this weekend and they were working fine. I did not put another 10A fuse in the Clearance light fuse because I didn't want the problem to blow my new headlights. Well, that worked for a couple days. Then this morning, the low beams went out, just happened while driving. Drove for about 5 more miles with the high beams on and they went out. How does this happen??? There must be a power surge that is routing through the light switch and out to the headlights? I'm now totally lost!!

Do any of the light wires route to the ECM? I replaced it about a year & a half ago but didn't experience any issues until now.


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## jp2code (Jun 2, 2011)

Make sure those fusible links are ....fusible links, and not solid wires. If your alternator's voltage regulator were going out, it could send spikes through your electrical. If you have a fusible link, the link burns up. If you don't, that spike goes out to the rest of your vehicle. It'd be good for your lights to catch the hit rather than some expensive electronic component.

Power to the headlights should go from the fuse block, to the light switch, to the headlights, and to ground. If something is burning those headlights out, you have more than 12V going to them.










Your taillights are on a different fuse circuit - unless someone modified your truck since 1986.










Notice: Everything shows the fuse block coming straight from the battery. The battery will get about as high as 13.8 Volts if the alternator is cranking out some juice.

If the voltage regulator is out on the alternator, the voltage could be anywhere.

You could swing the truck into an auto parts store to have the voltage regulator and alternator checked. If one of those are bad, you can be pretty sure someone has replaced the fusible links with hard wires.


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## jp2code (Jun 2, 2011)

Pics above have been resized by the forum.

For larger versions, right-click them and select "Open in New Tab".


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## 86HARD (Aug 18, 2014)

jp2code - Thank you for the diagrams. They actually look to be very similar if not exactly like my truck. For some reason, I was having trouble finding them on my own internet searches and the Chilton and Haynes that I got ahold of were no help.

I replaced the fusible links with new from Nissan about a year ago so I know they are not just solid wire that was rigged up along the way. Having the diagrams you provided above will help me. I'll absolutely check the voltage regulator on the alternator because if I have the clearance lights issue isolated without the fuse, it only makes sense that the problem with my headlights is coming from the power supply end, correct? Is it possible that there is power from somewhere else entering the headlight switch and then traveling through to the headlights? I'm borderline useless with automotive wiring so current flow can confuse me. I understand the basic principles but...

Thanks as always.


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## jp2code (Jun 2, 2011)

Power to headlights comes from the power supply end - as long as no one has spliced in some extra accessories to your truck.

I've heard of people wiring up fog lights to their headlight circuits. That draws extra power that could blow a fuse. I suppose it is just as likely that someone rigged up an extra relay with power from the battery that goes to the headlights. I don't know why someone would do that, but it would certainly cause issues that would be hard to track down.

The best way to think of electricity is to think of the Hoover Dam. That big dam holds all that energy, like a big battery. As long as it sits there, nothing happens. Opening a valve on that dam is like turning on a switch. Current (water or electricity) is allowed to flow. If too much flows, either a water pipe will burst at the weakest spot or your electrical component will burn out at the weakest component (the tiny light filaments). Water stops moving when it gets to the ground. Then, all of its energy is gone. The same thing goes for electrical current; it flows to ground and stops.


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## Shut-Trip (Oct 18, 2012)

86HARD: Did you resolve that issue? 

I had a similar issue with my tail lights completely going out with just the hazard lights and turn signal lights.

after several days of trouble shooting, and several post ( See my post in this forum). 

I discovered the problem. I had a short in my passinger side tail light bulb.

the odd thing was that the problem went away when I removed the Driver side taillight assymbly.

I still cannot explain that one, and dont care to try to explain that mystry.

But again, did you resolve issue? ...Plesae see my post in this forum)

shunt trip.


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## 86HARD (Aug 18, 2014)

I resolved the issue by wiring a dedicated loom for the rear lights. I was so tired of troubleshooting I just gave up on the harness. 

Also, the headlight issue is certainly not related. I was getting over 19volts to the headlights while at idle. This would explain why they kept blowing after a couple days. Replacing the alternator tonight and it should be good to go.


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## jp2code (Jun 2, 2011)

19 Volts.

I guess that'd cause problems.

Looking forward to the resolution.


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