I bought a set of these SMT LED tail/brae light bulbs from v-leds
NEW IMPROVED RED 7443 V-LEDS 7W HIGH POWER 20 LED BRAKE LIGHT BULBS 7440
They are 7443 bulbs as specified by sylvania (linked to by v-leds)
When I installed them on the car, strange things happen. Blown fuses, dimming bulbs... Long story short I looked at the way the stock incandescent filament bulb is wired, the way the LED lamp I bought works (uses a common ground) and the way the car is wired (shop manual wiring diagram). When I wrote v-leds they indicated that a Miata needs this version (indicated for a Toyota and Scion):
V-LEDS RED 48 SMT TURN/BRAKE LIGHT BULBS 7443-SRCK
Which is wired like this:


Looking at the way the stock filament is wired I am not sure this is right either. Though I want them to work, I am about to send the ones I ordered back. But I am checking here first to see if anyone knows WTF.

I read through Ben's thread here and it seemed to be plug-and-play for him though he did not order the same ones I did.
https://www.miataturbo.net/forum/t17324/

Thanks

 

Something else strange with the stock wiring. When I probe the pins in the connector for the tail/brake bulb, they all show continuity to ground. And that is with all of the front (park/turn) and rear (park/brake) parking light bulbs removed. Hmm...

Anyone?

 

Take a look at the wiring diagram sheets E-2 and E-3. One side is grounded the other goes to the TNS relay. You should have 12v across the relay contact when the lights are off and 0v when they're on. You may have fried the relay to ground.

 

******* hell where's the delete post button

 

Well it looks like something is not right anymore so the relay could be bad. I reinstalled the incandescent filament bulbs and the brake lights no longer work. There is a slight dimming of the parking lights when I press the brake so something is conducting power somewhere. Damn it...

I'll check out the relay later. Right now I am in the middle of reinstalling the engine. First things first.

 

Update:
OK V-LEDs sent me the Toyota style bulbs linked to above and they work. The parking lights and brake lights work normally again. So if you decide to get LED bulbs be sure to get some wired in the Toyota configuration. Either that or rewire your sockets.

 

Thanks for the update and for forging the way for others to follow.

 

Pics? Video showing the difference side-to-side?

Thanks for paving the way, you've saved other members who see this some headaches.

 

The LED parking light was slightly brighter than the filament bulb when viewed in daylight from behind. But it turns out the filament was burned out in the brake light on the remaining filament bulb when I tried to do a side-by-side brake light test. So when I replaced the incandescent bulb I installed the LED bulb to test the circuit on that side too. It turns out the brake circuits were still OK on both sides after all.

Also, if I read the wiring diagram correctly (Z-42), there is no relay for the brake lights, just the switch on the brake pedal. The circuit is: main bus fuse-> brake light fuse -> brake pedal switch -> brake lights (all three wired in parallel) -> ground