JeffWels

I'm having a rather odd electrical problem as it relates to my tail/brake lights.

Problem: The passenger side tail/brake light inside bulb (toward the center of the car) does not illuminate at all. Additionally the outside bulb is not functioning correctly. The outside bulb turns on fine with the running lights, but when pressing the brake with the running lights on it does not perform the 2 step function to become brighter upon braking. With the running lights off the outside bulb illuminates at the running light intensity with the pressing of the brake.

The drivers side tail light / brake lights function perfectly as they should with both illuminating and both performing the brake function correctly. All internal lighting, exterior lighting, functions as it should.

Things I have checked:
1. Fuses: checked, and replaced the stop and tail fuses in the driverside foot well box. These fuses were fine, but i know dirty electrical contacts can materialize in weird ways.
2. TNS Relay: I pulled and cleaned the contacts of the TNS relay and swapped the relay for the retractor relay next to it with no luck. Also gave the relay a good tap per some of the info i saw searching.
3. Bulbs: I have alternated bulbs all around the taillights, I'm certain all bulbs work as they should

Based on the symptom I don't think it is a light switch problem or a brake switch problem, but I certainly be wrong.

Does anyone know if there is a separate ground per side for the tails? I read here in an old post that the taillights share a ground, but I couldn't locate it.

Any help is greatly appreciated. My thought was maybe the wiring harness for the passenger side has some sort of issue, but the symptoms are very strange.

TomU

iTrader: (11)

check the connectors to the tail light assembly. I was having a similar problem. I switched to a 99 spec tail light and it worked, which seemed odd, but i never did any more troubleshooting since it worked. My guess is the connection may have been a little loose or dirty and when i switched tail lights it made a good connection.

Hot_Dog

You wrote that you "alternated bulbs all around the taillights". I recently had a similar problem. The problem started after I replaced a burnt out taillight bulb. Taillight would work fine but turn signal/stop light didn't work. Upon replacing the the original Japanese bulb (can you believe almost 30 years lifetime on a bulb!) with a Sylvania 1157 bulb, I discovered that I put the bulb into the socket the wrong way. It was a hard to reach corner spot and I had to work on it blindly. I thought that the bulb would fit in the socket only one way due to the staggered tangs on bulb's base. This is true for metal sockets but apparently not for a plastic socket. So, after rotating the bulb 180 degrees everything worked fine again. Not saying that this is your problem but it's worth a check.

JeffWels

I'm currently leaning toward maybe a tail light harness problem as well. I guess i can try to switch the tailight harness from side to side and see if that works.

JeffWels

I'm certain I have the bulb in the socket correctly as I actually changed all bulbs while I was in there. The issue materialized before I ever changed the taillights bulbs. Originally I thought that the bulb was out which prompted me to purchase a new one and replace it. That is when I realized it in fact wasn't a burnt out bulb, but something else.

I'm leaning toward trying to get my hands on another taillight harness for the passenger side and testing that way.

Does anyone know if the ground is the same for both sides or if they are independently grounded?

TomU

iTrader: (11)

just try to snug them up a little. You may also want to pull and see if you are getting voltage at the harness ends

Gen2n3

iTrader: (1)

Jeff,

I recommend that you save your money on a replacement harness until you know the root cause of the problem. I would also advise you to read the WDM (wiring diagram manual) for the proper schematics on the Parking Light system (Diagram E-3) and Stoplights system (Diagram F-3).

Double check all of the wiring going to the bulbs. Start at the bulb then work backwards. You may want to check the bulb housings for corrosion. The housings may have poor ground and cause some bulbs to work while others do not. You may be able to separate the metal housing from the plastic surround and clean any corrosion with a scotchbrite pad or fine sandpaper. To prevent corrosion from returning, you could use a thin film of dielectric grease on the metal shell. I had to do these steps on my front turn signal light and cleared it up. Additionally, inspect each connector for any signs of water intrusion and corrosion. You may find a pin heavily corroded or missing on account of electrolysis. Take photos and post as needed.

Cheers,
George

DaleClark

iTrader: (55)

The original tail light harnesses aren't great, Mazda did revise the design at some point. My '94 had weird issues where the brake lights would come on but not the running lights, etc.

The ground wire on the harness had a weak connection in the bulb socket itself. It was just a poor design.

I got new harnesses and have been good to go since.

Dale

JeffWels

Yes, my car is a 94! I am going to take some time and some pictures this evening and try swapping the harnesses side to side and bring my multimeter.

I also should mention the signals work fine on both sides.

Thanks all for the replies!

DaleClark

iTrader: (55)

If you do some searching I think I made a thread on the tail light harness.

Dale

JeffWels

It's definitely a harness problem. I grabbed a harness from a spare set of tails i forgot I had and that resolved the issue. I am still gonig to run tests on the old harness to see exactly where the problem is, just will do so off of the car.

Gen2n3

iTrader: (1)

Jeff,

It's good to hear that you resolved the problem. When you troubleshoot the wiring harness, pay attention to the wires within 1" of a connector. Roughly 90% of all wiring problems stem from this area. The 2nd most common failure point would be at a sharp bend. Let us know what you find out, please!

Cheers,
George

DaleClark

iTrader: (55)

My thread on it -

https://www.rx7club.com/3rd-generati...t-woes-890932/

You can see the poor design on the bulb socket side, that's the problem.

Dale

Gen2n3

iTrader: (1)

Dale,

As always, you are a wealth of knowledge! Thanks for sharing the link.

Cheers,
George