Parking and Interior Light fuse melting

[Captain Obvious]

Yup. That's what I'm thinking.

The thing that worries me the most though is that all of this started after some melties happening. I just hope it isn't melted insulation buried down in the harness somewhere.

If it's a bulb, even I could probably find it. However, if it's melted and shorted insulation somewhere in the harness, I'd need one of those RF signal sniffers.

[SteveJ]

The first thing to remember when doing the troubleshooting online, Bruce, is the Dr. House philosophy. Patients lie. Mind you, it's lies of omission, but the person with the problem didn't say what modification he/she made or what system he/she was messing with before the problem happened.

While there is a chance there could be something wrong with the dash harness, the main thing is that there is enough information to say that the GW & RL wires are short circuiting somewhere. The bad thing is that it's a 20A fuse in the circuit to protect wire that I wouldn't want more than 10A going through. I can't say if that's poor engineering on Nissan's part or if the standards for ampacity have changed between when the circuit was designed and now.

There are splices in the harness, too, where the wiring make the parallel circuit. These splices have a little bit of electrical tape covering them. When I was changing the light sockets on the speedometer on the 260, I used uninsulated splices covered with heat shrink and offset the splices to prevent overlap. I haven't taken apart the dash harness to see if they avoided overlapping splices.

[Captain Obvious]

Steve, Haha. Yeah, that's one of the things that gives me trouble with distance diagnosis. That and the ability to explain things in a way that others understand. It might make sense in my head, but being able to convey that info without writing a novel is a different story!

I found the same thing as you did with the buried splices. I'm planning some electrical upgrades (like headlight and starter relays) and have dissected a cadaver engine compartment harness for investigation. They did the same thing there. Splices crimped and taped and then buried in the outer layer of tape. Just hoping the fault isn't buried...

[Captain Obvious]

boosd,

SteveJ summed up the problem when he said that the Green/White wire is somewhere shorted to the Red/Blue wire. Problem is figuring out where that short is. Here's one idea that might help track it down:

Park the car in a dark spot (dark garage or just wait until it's dark out).

Turn the dimmer control to full dim.

Turn the combo switch to the first position (turn on the parking lights).

The parking lights should all be lit and the fuse should not be glowing.

Then quickly turn the dimmer to full bright and look at your interior illumination lamps. Don't keep the dimmer full bright for long because you're going to pop the fuse or burn something up again. But quickly look at the following:

speedo

tach

water/oil

amp/fuel

clock

lighter

heater control panel

radio

hazard sw

If you can't look check all of them in a second or two, just turn the dimmer back to full dim and give it a minute or two for everything to cool off. After a cool off period, do it again to check the stuff you didn't check the first time.

If any of those devices are NOT lit, I'd start there.

[Captain Obvious]

And I'm not sure if this is the most appropriate place for this, but since it's related...

While reviewing the wiring diagrams for the 260, I turned up a couple mistakes. I don't know if these are old hat already known issues, but since I'm not the keeper of 260's electricals (Steve?) I thought I would hand off to the experts. Here's a portion of the 260 (manual trans) diagram:

Here's what it should look like:

If there is a collective "Problems Found on the 260 Wiring Diagram" thread, this could go there. If there isn't a thread like that already, maybe one should be started? I know I've got at least one other 260 problem that I've discovered.

[boosd]

I will look at the dash lights tonight when i get home from work to see if one isnt lighting. I dont know if it is different on other models but my hazard switch doesnt have a light on it, just the defogger, choke, and fasten seat belts. I tried to get to the dash lights and dont see a simple plug, although I am going through the heater face/vents, is there a plug buried further back there or somewhere else, or do i have to pull each gauge out?

Oh its a 74 260z and nothing was modified before the initial burn up of the combo plug

Edited October 16, 2014 by boosd

[SteveJ]

The connectors for the lights are the connectors for the gauges. Then there is the socket that attaches to the back of the gauge. I would take pictures, but I'm overworked & have to fix the things my wife is breaking at home.

Make sure you look at the FSM. I gave you the page numbers.

[boosd]

The connectors for the lights are the connectors for the gauges. Then there is the socket that attaches to the back of the gauge. I would take pictures, but I'm overworked & have to fix the things my wife is breaking at home.

Make sure you look at the FSM. I gave you the page numbers.

I dont have an ohm meter, but hopefully this works... So far I unplugged Temp/Oil. Gas/Amp. and Clock one at a time, I still have the problem, tonight I will pull the tach plug and then speedometer

[SteveJ]

Don't forget about the lights in the center stack & center console.

[boosd]

Don't forget about the lights in the center stack & center console.

Pulled defroster, fasten seat belt, choke and heater face flip light, any thing else im missing?

Tried to disconnect the speedometer and the tach tonight, but I am unable to reach behind either anywhere near a connector or bulb, is there a trick to this or does the dash have to come out?

Edited October 17, 2014 by boosd

[SteveJ]

I believe you got all of the center stack lights. I never had luck in reaching behind the speedometer & tachometer.

To pull the speedometer & tachometer (assuming all of the fasteners are in place)

1. Pull the screw in the top of the bezel.

2. (Speedometer) Reach behind and unscrew the speedometer cable.

3. Contort yourself so you can see under the dash and remove the screw that holds the meter to the dash.

4. Pull the gauge forward through the dash. (Hope you don't have a full dash cap glued on...)

5. (Speedometer) Use a small screwdriver to loosen the set screw for the trip odometer.

It's a pain to get the trip odometer cable in place with the set screw tightened when you go to put it back in.

[Captain Obvious]

I dont know if it is different on other models but my hazard switch doesnt have a light on it, just the defogger, choke, and fasten seat belts.

I know the 74 was transitional in spots, but according to the wiring diagram, your hazard switch DOES have a light on it. Either your bulb is burned out, your connectors are corroded, or maybe that's where your problem is originating.

And about the other three... Defogger, Choke, and Seat Belts? None of them are controlled by either the dimmer or the combo switch. All three of those will always be full bright when their respective switch is turned on regardless of the position of the dimmer or combo switch. For example, the CHOKE indicator will come on full bright anytime the choke lever is pulled regardless of the combo switch or dimmer positions. Nothing is impossible, but it's unlikely that any of those have anything to do with the problem you are having.

If I were you, next thing I would do would be to disconnect the hazard switch and see what happens.

And you've been disconnecting things one at a time and then what? Reconnecting them or leaving them disconnected? If you've been reconnecting them, I wouldn't do it that way. I would disconnect something and leave it disconnected until you get to the bottom of the problem.