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No headlights and blinkers.. Help an electrical idiot!


Psychophoria

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After being apart for years, I'm finally reunited with my 73' 240z. Unfortunately, the headlights and blinkers are not functioning.. I'm hoping someone here can give me some pointers.

The hazards work/flash, the running lights work, brake lights work. The headlights very briefly worked, and we're very feint. The drivers side went out completely, and the passenger side followed shortly after.

At the headlight connector on the passenger side, I am reading 11.80v on the lowbeam lead and 11.65v on the high beam. The drivers side headlight connector doesn't read any volts at all.

Both the right and left headlights read 0.02v at the fusebox, white the other fuses are reading normal 11.64v. Hm..

The switch with 4 wires, connected to the right side light knob of the steering column seems to be working. I am reading 11.65v from the red wire, 11.79v on the white/red wire when the switch is turned on. There is continuity between them when the switch is on.

Nothing happens at all when the blinker knob is turned, although initially, the right turn signal indicator on the dash was constantly on despite the blinker itself not doing anything. The high beam seems to work though.

If anyone has some pointers or ideas, I'd greatly appreciate it. When it comes to electronics, I'm a complete dummy. Really hoping to have her on the road again soon.

Thanks all, and happy Thanksgiving!

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1 hour ago, Psychophoria said:

After being apart for years, I'm finally reunited with my 73' 240z. Unfortunately, the headlights and blinkers are not functioning.. I'm hoping someone here can give me some pointers.

The hazards work/flash, the running lights work, brake lights work. The headlights very briefly worked, and we're very feint. The drivers side went out completely, and the passenger side followed shortly after.

At the headlight connector on the passenger side, I am reading 11.80v on the lowbeam lead and 11.65v on the high beam. The drivers side headlight connector doesn't read any volts at all.

Both the right and left headlights read 0.02v at the fusebox, white the other fuses are reading normal 11.64v. Hm..

The switch with 4 wires, connected to the right side light knob of the steering column seems to be working. I am reading 11.65v from the red wire, 11.79v on the white/red wire when the switch is turned on. There is continuity between them when the switch is on.

Nothing happens at all when the blinker knob is turned, although initially, the right turn signal indicator on the dash was constantly on despite the blinker itself not doing anything. The high beam seems to work though.

If anyone has some pointers or ideas, I'd greatly appreciate it. When it comes to electronics, I'm a complete dummy. Really hoping to have her on the road again soon.

Thanks all, and happy Thanksgiving!

First, these are two COMPLETELY independent circuits.

Headlights first. The readings you give are inconsistent. Are you measuring voltage to ground when measuring at the fuse box? If they are essentially 0 volts to ground there, you wouldn't have voltage at the headlight connector, provided you have the dash harness to engine harness connectors correct. Since they are color coded, I would expect they are hooked up properly. 

There is only one voltage source going to the passenger headlight socket. The other two wires go back to the combination switch which will ground one circuit (high beam or low beam) or the other. If the headlight switch is on when the circuit is not grounded, you could see voltage at all three points on the connector if the other side headlight is plugged in.

Here's how the circuit flows:

  1. The white/red wire goes to the right hand switch.
  2. When the switch is on, there should be voltage on the red wire.
  3. The red wire goes to the fuse box and splits between the left and right headlight fuses.
  4. The right side fuse comes out as a red wire. The left side fuse comes out as a red/yellow wire.
  5. The wires go to the connector for the dash harness to engine harness and out to their respective headlights. 
  6. With the headlight plugged in, the wiring path goes back through the red/black (low) and red/white (high) wires
  7. The red/black and red/white go through the engine harness to the dash harness and back to the left switch.
  8. The left switch will connect one of those two wires to ground.

One of the first things to do is make sure you connected the ground wire at the steering column. A loose or missing ground will make your voltage reading wonky. 

The high beam indicator on the gauge goes from the right headlight fuse to the gauge and out as a red/white wire that joins up to the red/white wire that came back from the headlights.

For the turn signals, if there is not enough current flowing through the old flasher relay, the light(s) connected on that circuit will tend to stay on. You'll see this if there LED bulbs with the old style flasher relay. The old flasher relays would heat up with enough current flow. This would cause the bimetal strip in the relay to bend away from the circuit. This would cause the lights to go off. Once the current stops flowing through the bimetal strip, it cools, and the strip goes back into place, completing the circuit again.

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20 hours ago, SteveJ said:

First, these are two COMPLETELY independent circuits.

Headlights first. The readings you give are inconsistent. Are you measuring voltage to ground when measuring at the fuse box? If they are essentially 0 volts to ground there, you wouldn't have voltage at the headlight connector, provided you have the dash harness to engine harness connectors correct. Since they are color coded, I would expect they are hooked up properly. 

There is only one voltage source going to the passenger headlight socket. The other two wires go back to the combination switch which will ground one circuit (high beam or low beam) or the other. If the headlight switch is on when the circuit is not grounded, you could see voltage at all three points on the connector if the other side headlight is plugged in.

Here's how the circuit flows:

  1. The white/red wire goes to the right hand switch.
  2. When the switch is on, there should be voltage on the red wire.
  3. The red wire goes to the fuse box and splits between the left and right headlight fuses.
  4. The right side fuse comes out as a red wire. The left side fuse comes out as a red/yellow wire.
  5. The wires go to the connector for the dash harness to engine harness and out to their respective headlights. 
  6. With the headlight plugged in, the wiring path goes back through the red/black (low) and red/white (high) wires
  7. The red/black and red/white go through the engine harness to the dash harness and back to the left switch.
  8. The left switch will connect one of those two wires to ground.

One of the first things to do is make sure you connected the ground wire at the steering column. A loose or missing ground will make your voltage reading wonky. 

The high beam indicator on the gauge goes from the right headlight fuse to the gauge and out as a red/white wire that joins up to the red/white wire that came back from the headlights.

For the turn signals, if there is not enough current flowing through the old flasher relay, the light(s) connected on that circuit will tend to stay on. You'll see this if there LED bulbs with the old style flasher relay. The old flasher relays would heat up with enough current flow. This would cause the bimetal strip in the relay to bend away from the circuit. This would cause the lights to go off. Once the current stops flowing through the bimetal strip, it cools, and the strip goes back into place, completing the circuit again.

Thanks so much for such a detailed response, very helpful and informative.
I've been trying to diagnose the issue for the last few hours, and wow, I'm getting even more confused.

I started by checking the voltage in the fuse box, one cable of the multi meter on the metal fuse cap, the other end on a ground inside the car.
Light L, off: 0v, on: 0.02v... Light R, off: 0v, on: 0.02v... Flasher L: 0.05v Flasher R: 0.07v... Flasher middle: 0v There are other fuses in there I tested the voltage off, the park tail for example, on: 11.46v, off: 12.35v The other fuses seem to have normal voltage, and as I mentioned, all the lights work beside the headlights and blinkers.

At the right hand switch, with 4 solder points, I focused on the red & red + white wire. The red + white off: 12.36v and on: 11.78v.
The red wire off: 0v and on: 0.05v.. BUT.. after a few minutes, I measure it again and while measuring the red wire goes from 0.05v to 11.78v.

Up at the headlight plugs, one on each side of the horn, I measure the voltage by placing the multimeter leads onto the plug - one on the negative wire, one on the hi beam..then low beam.
On the passenger side, low beam: 0.02v... high beam: 0.02v. Then measuring drivers side, I suddenly high beam: 11.65v... low beam: 11.70v. WHAT? I go back to the passenger side, and am suddenly getting voltage there too, despite the fact that a moment ago I wasn't.

After this spectacle, I go back to the fuse box... I'm suddenly getting 11.78v on the Light L & R fuses, which confused me even further. I thought maybe the headlights would work, so I plugged them in, nothing.
I've located two grounds in engine bay, and I cleaned them quite a bit. One comes off of the battery, to the fire wall. As the wiring harness leaves the firewall, heading towards the front of the vehicle, there is another ground that comes out, which I also cleaned. I attached a photo showing where those two are located. Other than that, I can't seem to find any other grounds in the engine bay. I've heard people talk about a ground in the steering column, is that just the ground directly under horn cap on the wheel?

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Edited by Psychophoria
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Have you checked power in to the fuse box?  I don't know the early wiring well but if it was a 280Z you'd be checking the fusible links.  The 73 240Z electrical chapter is surprisingly oblique and unhelpful.

Also, as SteveJ inferred on the flashers, voltage can be present but current not guaranteed.  I would rig up a test light that draws a small amount of current, for your kind of problem.  Many people make up their own with a tail bulb or halogen head lamp. Two wires with a bulb in the middle.   Measure voltage then hit it with the test light.  If the light doesn't light, there's probably a break opening in the circuit somewhere, due to heat.  The meter doesn't pull enough to cause it.  If it does light, but not when the correct circuit is connected, then it's probably a ground problem.

Just some thoughts on breaking the problem in to smaller pieces.

p.s. I know that the backs of the 240Z fuse boxes can get pretty messed up.  Problem not visible unless you pull the box up.

Edited by Zed Head
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Ugh. You're gonna make me take off the steering column cover on my car, aren't you?

In the steering column, there is a ground wire that goes across under the column and plugs into a ground wire that runs back into the dash harness. If that wire is not securely plugged in, you won't have a ground for your headlights.

By the way, let's get this sorted out first, and then we can turn our attention to the turn signals.

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Working on the Z some more now..

I tested the passenger side headlight, powered it directly from the battery, and it works.

I found a ground underneath the center console/dash and cleaned it. I'm wondering if that is the one that has been mentioned, it's in one of the pictures below.

I cannot find any grounds near the horn. I think there were foglights at one point, so there are a few disconnected cables near the horn. There is one strange cable that ends abrupty in the front of the car, I followed it back to some sort of relay,you can see my finger touching where the wire plugs in.

One more mystery wire, white wire that goes into the firewall not part of the main wiring harness. You can it with the blue tip in one of the images. 20211126_213732.jpg

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Edited by Psychophoria
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Okay, so...

When the headlights are unplugged, voltage at the fusebox and the steering column switch is normal. When the headlights are plugged in, voltage drops to 0.04v.

 

Edit: nevermind, now the voltage is back to 0.04v with headlights disconnected.

Edited by Psychophoria
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Two suspicious wires are connected to the back of the fuse box. I'm thinking maybe one is AC line and one is headlight line?

 

Also found a melted portion of one of fuse sockets for park/tail fuse. I remember this from before from many years ago, the park/tail lights work. Despite that, I cleaned up the wire, recrimped it, and used a little hot glue to keep it from wiggling around. Would probably be best to replace this thing ASAP.

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1 hour ago, SteveJ said:

Your car has experienced the nefarious parking light fuse meltdown. You may want to consider the replacement fuse box from Motorsport Auto. https://www.thezstore.com/page/TZS/PROD/classic10a03/50-5010

The white/red wire going to the back of the fuse box is stock. The green wire with the forked lug is not stock.

I'm going to order one of those tonight. I powered everything back up after disconnecting the green aftermarket wire, but it sadly didn't affect anything. How does the fuse box look to you? Could that be causing the headlight problems?

I rebuilt and cleaned the switches last night on the steering column as well. There was some buildup in some of the areas, which can be seen in the pics.

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