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82 720 Diesel - No Running lights


SLO720

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Driving truck the other day and lost running lights. Headlight Hi/Lo works, and turn signals also.

 

Things I've swapped (known good parts out of another running truck)

 

- wiper switch

- headlight relay (both click when turned to running lights)

- all fuses are good

- dimmer switch

- ignition switch (electrical)

 

Also lost power to the injection pump controller.

 

From what I found the red wire that connects to the fusible links is a constant hot wire that feeds the headlight/running lights. 

 

What am I missing? 

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Don't trust a visual inspection of the fuses. Swap with a known good one or use a 12v test lamp on their exposed contacts.

 

 

Looking at the fuse box. Fuse #2 is the injection pump control, 15 amp. Swap with #3 or #4 both are 15 amp. 

 

You sure the fronts are out too??? Running lights, parking, clearance, license and dash are powered from fuse #13 or the 3rd one in from the far right. If not the fuse it's got to be the switch on the headlight/turn signal stalk.

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Just tried fresh fuses also, no change. The switch is working, it activates the headlights and kicks one part of the relay on for the running lights. 

 

So I another part of this is that my alternator decided to overcharge enough that it popped the fusible link at the battery. I used a link from an 83+ truck (all I have left for spares). Everything is getting power like it's supposed that I can tell.

 

I'll end up putting my vq35 alternator back on it for now I guess. 

 

I think my controller is fried as I tried to jump it and make it cycle and it won't. 

 

I may try jumping the relay or finding where I can add power to the running lights. I had running lights after the failure and new link. They just randomly died.

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Yeah, no exterior/interior lights lol

 

I have brake, reverse, turn signals, and headlight.

 

From what I've found, headlights and running lights are powered by the red wire that comes off the fusible links.

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   There’s a connector under the passenger seat, not the cab light delay relay look under the carpet there’s a connector. Separate and clean pins real good. Worked for me when my fuse kept blowing. 

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Headlight only, have their own fusible link, Green to a Red wire to the headlamp switch

 

Parking, clearance side marker, license light, interior light are on a Black fusible link going to a White wire to the fuse box for fuses 8 through 13. If your, brake lights, horn or heater fan work then the fusible link is ok. If the interior light works then the fuse is ok and that just leaves the headlight switch!

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It might sound funny since you’ve replaced and checked various other parts but my  82 720 diesel ‘s lights weren’t working yesterday and I went through replaced almost all of the exterior bulbs and put bulb grease on all connections and bulbs. I know it doesn’t match the problem you ran in to but just by me wiggling the rear connector going to the taillights completed the circuit for some of the peanut bulbs for the running lights. Process of elimination always helps. Hope you find a solution. Let us know. 

Edited by Diesel Dentures
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  • 2 weeks later...

Finally had a chance to go over the truck again and what solved the issue was unplugging the alternator harness from the main system. It's apparently causing a dead short in the system. I'll replace it next time I have the chance.

 

Might be sooner with it being diesel and the gas pumps around here dry from people panic buying lol. 

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That's pretty much impossible. The alternator has no connection to the running lights whatsoever. Save your old alternator there may be nothing wrong with it.

 

A short would blow a fusible link or start a fire.  

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It smoked two fusible links. I just didn't catch it the first time. Disconnected the wiring at the alternator the third time and hooked everything up with the alt unplugged. I'll put my vq35 alternator back on it and the 7.3 idi vacuum pump for now I guess

 

Was hoping to add back my a/c before summer came along this year 

Edited by SLO720
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My 720 has an issue with the wiring I think, the injection pump controller acts weird when the wire going to the oil pressure sensor is connected, after I removed it from the sensor the injection pump controller started working properly for a while.

With all the wires connected properly you have to have oil pressure to trigger the injection pump controller to move to the injection pump to the start position, if you remove that wire from the sensor the injection pump controller will move to the run position when you turn the key on as it thinks it has oil pressure with that wire removed.

Another thing it does is when you turn the key on the glow plug light in the dash comes on which is normal, if it briefly flashes and goes out that means there is something wrong with the alternator, it is unplugged, the fuse-able link is blown going to the alternator, or the plug connecting the fuse-able links to the positive battery post is not making a good connection, mine got hot and melted the plug housing a little, so every time the glow light flashed I had to pop the hood and get out and wiggle that plug till it made a connection, then the glow plug light would come on and stay on till the glow plugs were warmed up.

For some reason Nissan did some weird stuff wiring wise in the diesel 720s, I have had guys call me via an ad on craigslist that I was selling diesel parts, they would ask me why the engine would start but not shut down, I told them they had to cycle the plug going from the harness to the injection pump controller because it was stuck in the run position, but they did not understand, so they would drive all the way to my house so I could unplug the plug and plug it back in and the engine would then shut down, it just had a bad connection and one had to unplug it and plug it back in a few times till it worked.

So you think you smoked the black box(DPC Module)?, I do not have a lot of extras anymore but I just bought a bunch of diesel stuff a couple weeks ago which had one in the parts although I have not tested it yet in my 521 kingcab diesel truck which everything works properly unlike the 720 which I don't drive anymore so I don't care if it works properly right now, I just care that it starts when I want to start it and warm it up, anyway I am not selling them really cheap anymore but if your interested in one PM me, but I would first figure out if it is something else that is the issue, them DPC Modules do not go bad very often, it is usually something else like a bad connection in one of the plugs and when they put the other DPC Module in by unplugging it and plugging in the new to them one it works, but if they just cycled the plug the old one may start working again.

 

Another issue I have with my 720 diesel has to do with the headlights and running lights, since I don't drive it anymore when I start it and turn the lights on it can take several minutes for the running lights to come on, then when the headlights come on they are in the brights mode, but after a while they will click and be in the regular mode but if I even touch the headlight brights lever they will be back in the brights mode for another minute or longer, I found if I wack the steering wheel a few times making it vibrate it speeds up the process of getting back to the regular lights mode or even to get the lights to turn on, I do not know if this is a relay issue or a headlight switch issue or some other issue as the 720 wiring harnesses are weird, me and DatzenMike can go on about this issue but nothing get solved, also have your wired in anything to the headlight circuit to make a stereo or gauge light work that is not stock, that is a bad thing to do, it messes up everything in the headlight circuit, but the running light circuit is different, you can grab power from that circuit to make the aftermarket gauge or stereo lights work.;

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Hello sir, my headlights are on a separate circuit except for a signal to turn on the relays/switch to high beams. I'm running LED's on a cheap Amazon conversion harness.

 

I've noticed some of the circuits are odd and of finicky. I put a "T" at the il pressure dummy light switch so that I can run a manual gauge and a dummy light.

 

I have had to clean out a couple of headlight switches that did the delayed lighting thing. They build up grime between the contacts and that seems to be what causes that problem.

 

I also have several of the DPC modules and gave away 3-4 of them. One a couple weeks ago. Pretty sure I smoked the motor itself unfortunately. Once I switch the alternator I'll see if it'll go back to working. From what I remember the ip electric motors are different between sd22 and sd25 (clocked differently). I also have a few sd22 ip motors. 

 

I've given away parts to a couple guys in the facebook 720 group. I have parts for the most part and have been trying to keep as many of these things on the road as I can.

 

Do you know of anyone that rebuilds the DPC modules? Or other hard to get electrical parts?

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I have never had a bad DPC Module, I have never had an issue with the glow plug timer either, a local guy fixed his DPC Module once but it went bad again and he came back and bought one from me, other wise I don't know anyone that has ever worked on one except maybe Al on the Nissan Diesel Forums, I have had issues with the Injection pump controller, one just quit working, and the other nuts holding the motor on came loose and it fell apart, I just used an SD22  injection pump controller and it works just fine on my SD25 engines.

I also tried putting a adapter where the oil light sensor switch is to run a electric oil gauge and it broke off and oil puked out all over the road, lucky for me it broke just before I entered a parking lot and parked, as I was walking into the store I seen a trail of oil and thought someone had a bad leak that turned out to be me, I had to go home to get tools to get the broken threads out of the oil port so I could put the oil light sensor back in, since my engines are turbocharged I put one of them sandwich things between the oil filter mount and the oil filter and that is how it has been since as it was too big a hassle to put it at the oil feed for the vacuum pump port, my electric oil gauge was acting weird so I put a mechanical one in also, then the electric one started working correctly, so I have 2 oil gauges and no light because the engine would not start with it connected.

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9 hours ago, SLO720 said:

Hello sir, my headlights are on a separate circuit except for a signal to turn on the relays/switch to high beams. I'm running LED's on a cheap Amazon conversion harness.

 

I've noticed some of the circuits are odd and of finicky. I put a "T" at the il pressure dummy light switch so that I can run a manual gauge and a dummy light.

 

I have had to clean out a couple of headlight switches that did the delayed lighting thing. They build up grime between the contacts and that seems to be what causes that problem.

 

I also have several of the DPC modules and gave away 3-4 of them. One a couple weeks ago. Pretty sure I smoked the motor itself unfortunately. Once I switch the alternator I'll see if it'll go back to working. From what I remember the ip electric motors are different between sd22 and sd25 (clocked differently). I also have a few sd22 ip motors. 

 

I've given away parts to a couple guys in the facebook 720 group. I have parts for the most part and have been trying to keep as many of these things on the road as I can.

 

Do you know of anyone that rebuilds the DPC modules? Or other hard to get electrical parts?

 

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I imagine the light switch is the same as the gas model. My lights were all messed. I had to remove the steering wheel and remove the switch assembly from the steering column. I took it all apart (lots of small parts to have a place to lay it all out) and clean all the electrical contacts. Put it all back together and it works perfect

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