1 minute ago, Zed Head said:

Stretttccchhhh - the indicator bulb in the tachometer (speedometer?). Can't find it in the wiring diagrams but I know it's connected somehow.

I replaced all the dash bulbs with LEDs before I did the taillights but I'll add it to the list of things to check out when I have a few hours.

I guess worst case, I end up redoing the body harness early then planned since that is something I'd like to do at some point.

20 hours ago, Electrin97 said:

Put the left side into mode 1 (normal blinking) and kept the right side on mode 3.

Can you post a video of this test? And can you make sure it's possible to see the state of the front turn signals as well? Don't need a mirror or anything that complicated... Just make it such you can see the glow or reflection from the fronts so we can see what they are doing at the same time?

Your description of the results didn't make sense. Probably just a simple typo, but it would be best to just post another quick clip.

20 hours ago, Electrin97 said:

Once the car was running, right side still had a cycle of 1.25 with an 80% duty cycle but the right side was erratic.

You mentioned right side twice?

Also... All of your tests posted so far are when using the four-way flashers. Is this problem the same when using the turn signals instead of the four-ways?

Just trying to determine if it has anything to do with which flasher unit is being used. I doubt it, but it's easy to determine.

Here's why I mentioned the non-standard Nissan Sealed Beam connector wiring. They essentially wire it backwards (because they want the switch to control negative rather than positive) - Hot to the standard ground connector, then Ground(s) to what would normally be the "+" side of the low & high beam filaments. The dimmer switch controls the "direction" of the ground from High to Low Filament. It might be interesting to disconnect the headlamps temporarily and see if that has an effect on the turn signal function.

I installed some (Amazon) Halo LED Headlamps for a young man's 240Z here in the Phoenix area several months ago and they required changing the Nissan wiring scheme to the "standard" sealed beam plug wiring. I was wondering why yours just plugged in - and worked...

I agree, Eliminate one variable at a time.

On 1/23/2026 at 6:59 AM, Captain Obvious said:

Also... All of your tests posted so far are when using the four-way flashers. Is this problem the same when using the turn signals instead of the four-ways?

Just trying to determine if it has anything to do with which flasher unit is being used. I doubt it, but it's easy to determine.

Same issue when using the turn signal, its just easier to visualize with the 4 way flasher on.

On 1/23/2026 at 6:56 AM, Captain Obvious said:

Can you post a video of this test? And can you make sure it's possible to see the state of the front turn signals as well? Don't need a mirror or anything that complicated... Just make it such you can see the glow or reflection from the fronts so we can see what they are doing at the same time?

Your description of the results didn't make sense. Probably just a simple typo, but it would be best to just post another quick clip.

You mentioned right side twice?

Yeah, that was a typo, erratic side was supposed to be left side. I can video tape the test later today.

On 1/23/2026 at 1:56 PM, cgsheen1 said:

Here's why I mentioned the non-standard Nissan Sealed Beam connector wiring. They essentially wire it backwards (because they want the switch to control negative rather than positive) - Hot to the standard ground connector, then Ground(s) to what would normally be the "+" side of the low & high beam filaments. The dimmer switch controls the "direction" of the ground from High to Low Filament. It might be interesting to disconnect the headlamps temporarily and see if that has an effect on the turn signal function.

I installed some (Amazon) Halo LED Headlamps for a young man's 240Z here in the Phoenix area several months ago and they required changing the Nissan wiring scheme to the "standard" sealed beam plug wiring. I was wondering why yours just plugged in - and worked...

I'll try disconnecting the headlights and see if that does anything. Since the headlights I bought were supposed to be direct drop ins and not generic 7" lights, I assumed the company I bought them from would have made sure the polarity of the connectors was correct (I'd also assume that if it wasnt, the headlights would not turn on at all due to them being LEDs).

List of things I will be testing soon, I will reply to this messages with results as I do them.

1. Run a direct ground to the battery and the turn signal wiring

2. Disconnect headlights

3. Swap LED headlight units and see if rear turn signal issue follows

4. Run the fuel pump with the engine off to see if it is inducing electrical noise

5. Direct wire the pink +12v wire to the positive battery terminal or an external power source

6. Swap the turn signal and the 4 way flasher relay

7. double check the voltages on the boards themselves.

8. Take a video of the condition that Captain Obvious requested earlier

Ended up taking a break from this issue due to a leaking brake MC and some other issues but finally got back to it. I tried everything on the list above and still wasnt able to narrow it down. I ended up running a gound directly to the battery for the turn signal circuit on my halo headlights and that helped but the right and left turn signals are still not synced while the engine is running. They are a lot closer in cycle speed now and I'm going to call it good for now since I am planning on making a new body harness eventually and that should (hopefully) fix the issue for once and all.

Thanks for the help everyone.

I'll make a new thread for it but I also ended up designing and having some oil fill caps printed out of Al since non of the options on the market spoke to me or where more expensive than having some custom ones 3D printed!

2 hours ago, Electrin97 said:

having some oil fill caps printed out of Al

What material is AI?