I'm running into a weird issue that I've tried chasing down but am at my wits end. I retrofitted these sequential LED Brake/Turn signal boards (https://www.dapperlighting.com/products/1974-1978-datsun-260z-280z-advanced-sequential-led-tail-lights) a few months ago and everything worked as expected. At some point, when the driver's side turn signal was active, it would flash erratically (not at half frequency) but only while the engine was running, if the engine was off the turn signal behaved as normal. This is also only when in a sequential mode, if I disable sequential mode, the turn signals flash as expected. When I did the retrofit, I also installed new flasher relays that are supposed to be low voltage ones for use with LEDs. I have contacted the company that makes the boards and they havent been much help.

Things I've done to troubleshoot:

Move the sub harness between drivers and passenger side; issue is persistent on left side

Plug in passenger side turn signal to driver side harness; issue is persistent on left side

Check continuity on all grounds for the harness

Check alternator for steady 14.4 V

Check turn signal trigger signal between left and right

Bench test the LED boards with a battery pack

The problem is related to something on the left light body harness but I have no idea what it could be, especially since the sequential turn signal works fine when the car is off but not while its running. Any help would be appreciated.

I'll upload some videos when I get home later today

55 minutes ago, Electrin97 said:

the sequential turn signal works fine when the car is off but not while its running.

This seems like a voltage problem, since voltage would be higher with the engine running. Or possibly a voltage quality problem from the alternator. Ripples or spikes or noise or similar.

If it was mine I think that I'd pull the boards and switch them for a test. If the problem stays on the driver side it's the harness, if it switches it's the board. Or if there's enough play in the harness switch the wiring. You might have a board that's sensitive to the higher voltage or the quality of it.

Basically - collect more clues. Determine if it's the board or the harness. There are many components on the board, any one of which might cause a problem.

Looking at what you've tested already it certainly does seem like a wiring harness problem.

I've recently been making some changes on my Early 260Z during which I discovered some MAJOR oxidation in my GROUND wiring. It surprised me greatly AND led me to completely rewiring the engine bay harness. Unfortunately (or fortunately), that's not where I stopped but that has nothing to do with this tale. My 260Z has lived it's entire life in Arizona where we don't see much moisture so the condition of the ground wires really surprised me - they were much more oxidized that the power or signal wiring in my harness.

Continuity is one thing but amperage is key. I used to say this all the time - though usually I was talking about EFI engine harnesses - CLEAN all your connectors and check the condition of your wire.

Starting with the 260Z, Nissan was using more (better) weather-tight connectors than they did in the 240's (which were not at all) but the ground wiring has many open barrel crimp connections inside the harnesses that are merely tape wrapped. I would check connector pins and sockets for corrosion first.

Next thing (and perhaps the first thing) might be the turn signal switch itself. LEFT is usually the thing that goes wonky first in the switch since the lever moves the switch UP and against the gravity force. As the parts inside the switch age they don't move as positively into position. And - at this age - there is generally a lot of wear on the contact points in the switch which means deterioration and/or carbon build up. I have no idea how that would cause the stated issue but with the experience I've had dealing with Z cars I never say never...

19 minutes ago, cgsheen1 said:

Looking at what you've tested already it certainly does seem like a wiring harness problem.

I've recently been making some changes on my Early 260Z during which I discovered some MAJOR oxidation in my GROUND wiring. It surprised me greatly AND led me to completely rewiring the engine bay harness. Unfortunately (or fortunately), that's not where I stopped but that has nothing to do with this tale. My 260Z has lived it's entire life in Arizona where we don't see much moisture so the condition of the ground wires really surprised me - they were much more oxidized that the power or signal wiring in my harness.

Continuity is one thing but amperage is key. I used to say this all the time - though usually I was talking about EFI engine harnesses - CLEAN all your connectors and check the condition of your wire.

Starting with the 260Z, Nissan was using more (better) weather-tight connectors than they did in the 240's (which were not at all) but the ground wiring has many open barrel crimp connections inside the harnesses that are merely tape wrapped. I would check connector pins and sockets for corrosion first.

Next thing (and perhaps the first thing) might be the turn signal switch itself. LEFT is usually the thing that goes wonky first in the switch since the lever moves the switch UP and against the gravity force. As the parts inside the switch age they don't move as positively into position. And - at this age - there is generally a lot of wear on the contact points in the switch which means deterioration and/or carbon build up. I have no idea how that would cause the stated issue but with the experience I've had dealing with Z cars I never say never...

Refreshing the combi switch is one of the first things I went through when I got my z! Even had to reverse engineer and 3D print a couple of the internal plastic components that had become brittle and cracked over time.

I'll double check all the grounds for corrosion and go from there.

First video is when I first wired up the boards and second video was today. So something happened at some point between the two but not sure. It does seem to be a ground issue.

1 hour ago, Zed Head said:

This seems like a voltage problem, since voltage would be higher with the engine running. Or possibly a voltage quality problem from the alternator. Ripples or spikes or noise or similar.

If it was mine I think that I'd pull the boards and switch them for a test. If the problem stays on the driver side it's the harness, if it switches it's the board. Or if there's enough play in the harness switch the wiring. You might have a board that's sensitive to the higher voltage or the quality of it.

Basically - collect more clues. Determine if it's the board or the harness. There are many components on the board, any one of which might cause a problem.

It's definitely driver side body harness. I'm lost where to start looking at the harness though. I tried videoing the trigger signal on my multimeter to see if there are differences in peak voltage and frequency they switch at but it was hard to see anything concrete with just a multimeter and not a scope, passenger side might be around 1 sec slower for a cycle but its hard to tell.

1 hour ago, Electrin97 said:

It's definitely driver side body harness

How do you know?

5 minutes ago, Zed Head said:

How do you know?

I've swapped driver and passenger side boards, sub harnesses, and bench tested both boards, the issue is always on the drivers side and there were no issues when bench testing the boards.

The difference between running (alternator power) and not running seems like it should mean something. Something odd like ground loop currents. I assume that the boards have small microprocessors. Maybe they're sensitive.

Instead of trying to find a bad ground you might try adding new grounds. See what happens.

Only in the rear? (oh, paid attention to the video, so never mind... In the sequential mode the flasher must be ignored - so those lights require a constant positive source for controller and lights.) The Z will have a ground to frame connection in the rear - Wire with eyelet bolted to the sheet metal on the right side I think. But most of the wiring back there including the fuel pump should use that ground I believe... I still don't see why any of that would cause the problem.

Zed Head has a point. Many of the new controllers use 3.3 to 5 volts (most 3.3) and generally are tolerant of higher voltage only up to a certain point. But that wouldn't explain why it behaves normally everywhere but the left side. Both voltage and ground hit the back on the right side of the chassis and travel to the left - meaning that is how the harness is laid out - It starts in back of the glove box -> passenger floor right side -> into the right quarter panel and over the wheel well -> along side the evap tank and fuel filler -> to the right side tail lights -> license plate lighting -> left side lighting -> radio speaker and antenna.

As he said, a hank of wire to temporarily provide a new ground straight from the battery to the light - good test. If not that, logic dictates that the only change between connecting it to the right side and left side would be the wiring between the two...

And you're aware that there are two separate flasher units - one for the turn signals, a different one for the emergency flashers. Weird problem...

Edited January 22Jan 22 by cgsheen1

Weird. It should not be doing that.

So the first thing that catches my eye is... When the hazard flasher is in it's OFF state, neither side should be lit. At all. And when the hazard flasher is in it's ON state, both sides should START their sequential slide across the bulb face. Yours get completely out of sequence and sometimes your left side even remains lit when the hazard flasher is in it's OFF state. That should never happen.

The sequential feature requires the running of a new power wire (pink) to the rear of the car, but that wire is not necessary if you are running the lights in standard mode (not sequential). My spidey sense is telling me to check the integrity of that wire.

Can you program your assemblies to function in standard non-sequential mode and see what happens?

Next, can you put just the left side in standard mode and see what happens? (Left side in standard non-sequential and right side in sequential mode 3 - in to out and back)

Also, what year are you working with? I'll look at the wiring diagrams.

12 hours ago, cgsheen1 said:

Only in the rear? (oh, paid attention to the video, so never mind... In the sequential mode the flasher must be ignored - so those lights require a constant positive source for controller and lights.) The Z will have a ground to frame connection in the rear - Wire with eyelet bolted to the sheet metal on the right side I think. But most of the wiring back there including the fuel pump should use that ground I believe... I still don't see why any of that would cause the problem.

Zed Head has a point. Many of the new controllers use 3.3 to 5 volts (most 3.3) and generally are tolerant of higher voltage only up to a certain point. But that wouldn't explain why it behaves normally everywhere but the left side. Both voltage and ground hit the back on the right side of the chassis and travel to the left - meaning that is how the harness is laid out - It starts in back of the glove box -> passenger floor right side -> into the right quarter panel and over the wheel well -> along side the evap tank and fuel filler -> to the right side tail lights -> license plate lighting -> left side lighting -> radio speaker and antenna.

As he said, a hank of wire to temporarily provide a new ground straight from the battery to the light - good test. If not that, logic dictates that the only change between connecting it to the right side and left side would be the wiring between the two...

And you're aware that there are two separate flasher units - one for the turn signals, a different one for the emergency flashers. Weird problem...

Not sure if its the standard ground but it looks like the ground for that section of harness is directly in the middle of the trunk, right behind the license plate. I'll try running a new ground directly from the battery to check.

Both flasher relays were replaced with the units recommended for the boards.