Here is what doesn't work.
NO headlights, low and high, ...only pulling the switch toward you for high beams works
NO parking lights. Dash lights, tail lights.

Turn signal and brake lights work

Tns relay is good. Tested it on my Eunos Cosmo, headlight relay and fuse is good. Meter fuse inside the cabin is good.

I temporarily added a ebay DRL kit to keep me able to drive.
While I did testing, if I test the headlight relay, power is on all legs except white/green. Tns relay has power on the grey wire. And the incoming wires. But no power on red wire,.

I ran power to the tns relay red wire and headlamp relay white/green and I got everything working. As a temp fix.
I had issues with tire/harness contact years ago but I checked and nothing is rubbed. Possibly combination switch ?

 

Hands down most common problem is the tire going through the wiring harness. You have to REALLY look, like pull the tire off and get up in there.

If you did have contact back in the day it's possible the wires have degraded further and are now broken or shorting. In that case pull the fender liner and check it all out.

Also check fuses. If you have an aftermarket car stereo it's possible that the wiring to the stereo could have shorted or acted up and caused issues - it typically ties into the dimmer circuit.

Dale

 

I went through it again today, the tns relay is bad. That's been fixed. But still ho headlights . The wire that runs from the power side of the headlight relay I'm the fender well was traced and is good with no bare spots.. the relay isn't getting signal from the switch.

Switch is no longer available. Any chance a Miata one will work ?

 

Combo switch?
We have two good ones.

 

You can open the the headlight switch very carefully and you might just have some build up on the parts that send power when the **** is turned to the "on" position. Use a green scuff pad or light san paper and carefully reassemble . I'm on my second one but in the mean time you can hook up a toggle switch to get by if it fails again. You can also tap into the harness and have the low beam switch turn both low and running lights on

 

This might sound like a "dumb" question, but did you trace the circuit and verify power at each step? Passing and Dimmer Switches both pass 12v, The actual Headlight Switch and TNS Relay switch contacts supply a Ground. Take a careful look at the Wiring Diagram for the headlights, Section E-2 in the Wiring Diagram book and start tracing the circuit. Ground points 1 and 2 are used for pretty much everything here, including the Fog Lights.

If it's a Japanese FD, I can help you trace the circuit. I just looked at the diagrams and found it was wired backwards from the factory, forcing all of the current through the switch. If you have my Wiring Diagram book for the Eunos Cosmo, Look at Section E-1 to see how a correctly designed headlight circuit works. Switch triggers relays that do all of the heavy lifting. And really, if you have a Cosmo, you should have it anyway...

If you decide to open up the combination switch, it will likely look about like this, from my 97 Expedition. Despite cleaning it up, it was beyond saving.
https://www.ford-trucks.com/forums/1...0-pickups.html

Soon as I got the Expedition, I added relays into the circuit so the new combination switch (thank you Rock Auto) would only be passing about 1 amp to trigger them for the headlights (low and high respectively). Worked like a charm and still works like a charm to this day.

 

currently I have a ebay auto on at night kit installed. Has a light sensor and works great n also has a on-override button. But I do want to get my car back to OEM working order

 

I can't remember off the top of my head if the switch sends a ground or a power supply I'll have to look at the diagram again. My other option was going to be run a new set of wires straight from the switch to the relay that way I know there is no broken wires along the way, if that works I'll simply rewire it as so.

I do have your Cosmo book. It's the digital copy.

 

So I just checked the USDM wiring diagrams and it's wired identically to the Japanese ones in this area. At the Combination switch, Red/Yellow is Low Beam, Red/White is High Beam and RED is power from the 30A HEAD fuse. To test the circuits, unplug the Combination switch, then connect a Jumper wire between the RED wire and the Red/Yellow to test low beam wiring, Red to Red/White for high beam. If they come on, your switch is the issue. If they don't, your harness needs repaired.

As for retrofitting relays, it's a simple, cheap mod that should be done regardless of age or lighting plans so one doesn't fry their now-NLA switches. A 4-pack of 40A waterproof relays with socket pigtails is $16 shipped on ebay right now from several different sellers. You can do it with other relays or a relay box too, this is a subjective matter to suit your own needs for fit & finish.

Find a spot under the hood that the harness is accessible from on the driver's side, then cut the Red/White and Red/Yellow wires. Anywhere along the frame rail is fine, just make the cut before it jumps across to the passenger side along the front of the car. Then wire in two relays as follows:
Pin 85: Red/White (Low Beam: Red/Yellow) on the Switch Side
Pin 86: Ground
Pin 30: Fused 12v power (I'd tap into the 30A Head fuse for consistency)
Pin 87: Red/White (Low Beam: Red/Yellow) on the Light Side

Your lights may be slightly brighter since it's taking a MUCH shorter path between Fused 12v and the headlights themselves, eliminating voltage drop from the switches and harness from the equation.