Tail light mayhem on my 86 targa

[shuzboomer]

Hello fellow pelicans,

After getting my car put back together after a full re-spray, I developed a variety of electrical gremlins that I have been slaying one at a time.

The latest one has been kicking my butt.

In a nutshell, my passenger taillight does not work. By tail light I mean I have no lights on when I pull my light switch one click on the light switch. I also have no lights with the light switch pulled all the way out with the engine running.

The tail light, as far as I can tell consists of the small single light bulb mounted in the far right socket and one half of the two conductor bulb on the opposite side of the light assembly. I believe this same bulb is illuminated when applying the breaks.

One item that I wanted to also mention is that with the light switch in the off position, I am able to illuminate my tail light by turning my turn-signal indicator to the right. I think this mode is called parking light feature on our cars. These are the same bulbs that don’t work when the light switch is pulled one click or when headlights are turned on.

Also not working, is my passenger side forward facing running light. This light is normally illuminated when you pull one click on the on the light switch.

Here is one item that I observed that is making me scratch my head....



Here is what I have already tested and

1. All fuses and light bulbs
2. The ground for the fixtures
3. The round connector in the engine bay that feeds power to the light fixture.
4. Driver side tail light works like a champ...

I hope my description of the problem is detailed enough for someone to shed some light on my problem.

I can send some pics if needed but as of this moment I need to step away from the vehicle and put down the test light...

[FrankM_]

If you put 12V from the battery at the terminal 4 (use long cable from a know, measured 12V point - battery ground connected to car) does the light light up ? If not, you do still have a ground issue on the tail light assembly or a connection issue between the bulb and the socket.
Same for terminal 3 : that should trigger the break light.



If it lights by putting the 12V on it, you know the assembly and ground are OK from the connector onwards. Then you have to check the wiring and especially the connection to the fuse block. You say you have checked the fuse (nbr 6 I believe for the right side) but did you check that the GREY/RED cable is connected correctly on that side ?

If you put your lights switch on, do you get 12V at the arrival and departure end of the fuse ? Looking at the diagram, I see that our cars (this diagram is for a '85) have a L (left) and R (right) output terminal on the light switch itself, so also at that point there could be a problem with the connection. Check the back of the light switch if you do not measure 12V with a voltmeter to fuse 6.
Given your specific problem (rear right and front right) I believe the problem is in the connection to the light switch or the 'NR 10' connector you see on the lower right near the light switch. It would explain the 'one sides problem front & rear'.




PM me with your email if you need the wiring diagram for the MY85-86 to debug further.

[FrankM_]

Better view of the light switch (correctly stitched).

[shuzboomer]

Hey Frank,

Thanks for the info can’t wait to test.

[shuzboomer]

Spent some more time testing... here are the results.

Applying power to the light directly has ruled out any ground and or bulb contact issues with the light fixture.

When testing for current across fuse #6 I discovered that no current was flowing when light switch was pulled either for parking lights and or headlights turned on.

The fuse in question has a gray/red wire going to the top of the fuse and a gray/red at the bottom, there is also a black/red wire that is also attached to the bottom of the same fuse terminal.

My next place to poke is the light switch... just checked the price of a new one “ouch!” I hope the problem is somewhere else...

If anyone has additional suggestions... let them fly!

Thanks in advance

Shuz!

[timmy2]

Wiggle and push on the light switch’s wiring harness 6 pin connector at the bulkhead.

Is this the one of the years with the diode in the right side wiring?

[shuzboomer]

One more update...

While I don’t have power at the switch when I turn on the light switch, I do have power at the switch.

By putting a meter between the wire and it’s respective post I get 12 volts when I pull my light switch.... I think this means my switch is good.

Hmmm... where do we go from here?

[shuzboomer]

Originally Posted by timmy2

Wiggle and push on the light switch’s wiring harness 6 pin connector at the bulkhead.

Is this the one of the years with the diode in the right side wiring?

I don’t know about the diode... looking for a wiser pelican to chime in.

Shuz

[86 911 Targa]

^^^^^
Diode location to the right of the steering column.

Not sure it is the diode, as the body shop did not have access to the diode.


^^^^^
I would check the wire colors with a schematic.

pm me as needed.

Best,

Gerry

[FrankM_]

Originally Posted by shuzboomer

Spent some more time testing... here are the results.

Applying power to the light directly has ruled out any ground and or bulb contact issues with the light fixture.

When testing for current across fuse #6 I discovered that no current was flowing when light switch was pulled either for parking lights and or headlights turned on.

The fuse in question has a gray/red wire going to the top of the fuse and a gray/red at the bottom, there is also a black/red wire that is also attached to the bottom of the same fuse terminal.

My next place to poke is the light switch... just checked the price of a new one “ouch!” I hope the problem is somewhere else...

If anyone has additional suggestions... let them fly!

Thanks in advance

Shuz!

First : send me a PM with your email, I have the PDFs with the correct MY86 wiring schematic ready for you, including the fuse box wiring. That will help greatly in following the current path and all elements involved.

1. Good to know the assembly and ground is OK 👌

2. We knew no current was flowing, otherwise the lamps would have worked given 1 ;-)
Did you measure current through the fuse (Amps, meter in series) or Voltage at the fuse ends vs GND, just to be sure ?

3. Does your right license plate light work ? Apparently on the 86 it is fed from the 'R' terminal on the light switch ? This way we can see if the R terminal gets power at least when the lights are switched on.
If so, it could still be that :
- your connection of the cable running to the lights is not good on the back of the light switch (second cable on 'R')
- the diode went bad
- you have a wiring issue somewhere inbetween (fuse box connections, other connectors)

4. I would remove the light switch from the dash (not too hard) with ALL cables left connected as they are and measure volts across the L and R terminals with the lights switch in different positions. This is the source where the current should come from so better measure there first.
There is a diode involved on the 86 apparently (not on my 85), if I read the diagram correctly it has to do with the right side and parking light operations (see top of the image here, part 911 617 108 00)





Happy hunting

[86 911 Targa]

^^^^^
Correct switch wiring as per our M/Y 1986.

Gerry

[shuzboomer]

Hello fellow Pelicans’

What an amazing response to my question. I would like to report that the mystery of the non-functional passenger side tail light has been solved.

I would like to thank all that contributed to this thread. I especially want to thank frank for sending me PDF gold.

At the end of the day the root cause of the problem was a bad diode pictured above.

When troubleshooting at the headlight switch, I also discovered a few wires with compromised insulation. I don’t believe the insulation had anything to do with my direct issue. However, I took liberty to do some preventative maintenance before I developed other problems.

Below are few picks that I took which others who trip over this thread may find useful.

To summarize my lessons learned.

1. You need to have the correct wire diagram to help identify the correct wires (colors) that are responsible for delivering power to your light fixture.
2. Test you bulbs and fixture by connecting a know good hot 12v source to your fixture. Often times one bad bulb or ground will sink your boat.
3. Once you rule out your fuses, bulbs and fixture, you want to work back from you tail light fixture to the round terminal connection that can be found in the rear fender. Many have solved their problem by simply wiggle this connector.

4. If your problem is not resolved, your next plan of attack is the light switch itself or like in my case the wires that plug into the back. The switch can be removed with little difficulty or if you like working with blood rushing into your head; you can visualize the back of the switch from the driver footwell.

Thanks again for all who helped and thanks to our host for having the diode in stock. I expect delivery just in time for the weeked!

Cheers!

Shuz.

[FrankM_]

Good to have that sorted.
If you are working around that area anyway : please insert a fuse on the interior lights (term 58a of the light switch and 3 black/blue wires) and the grey wire for the ashtray light.

I fused both coming from the light switch with a 3 A inline fuse after reading the excellent tread on the risks of these unfused circuits !

[86 911 Targa]

Have a look at my posts.

Added fuses and relays.

Gerry

Gerry