Turn signal wiring: '87 911 and '77 911 have the same but opposite problem

[carmencarerra]

I have an '87 911 and my partner has a '77 911. My right turn signal does not work. His left turn signals don't work. We've both replaced our turn signal stalks in the last couple months to see if it would help. It didn't.

So I took a look at his fuse box and noticed that his left blinker wire had one wire going in the top and one going in the bottom and one was just chilling dangling about. His right blinker had two and two. I plugged in the dangling wire and his turn signals started working! Until we replaced the light bulb and then it stopped....and then the low beams also went.

After his started working (albeit briefly), I looked at my fuse box and noticed my RIGHT blinker wire had two going in the TOP and one going in the bottom with one just dangling about. And my left had two and two. I plugged in mine...nothing happened. I then decided to change that spark plug for funsies. Now I have blown EVERY fuse I have put in there and have tried different amps (5,10,15 when stock is 5) even when I undid the added wire.

What is going on?? Why did we both have one blinker wire unattached? Is that a thing that was done intentionally for some reason?

Can someone provide some troubleshooting tips?

If it helps, our cars have been modified by pervious owners: Mine had A/C & heating ducts removed and added DC19 cams. His has the same and he added a hot rodded engine and carbs.

[zuch]

Do you have wire colors (a picture would help)? The two wires feed front and rear signal lights. Unless somebody has changed the wiring, you need both wires to get turn signals front and rear. When you say "the turn signal doesn't work" does that mean neither front nor rear work on that side (and same for your partner's)? You may have a short in one of your turn signal housings if you are blowing a fuse. If you tell me wire colors I can tell you where to look. Do your emergency flashers work?

[gerakroo]

For the 1977 car, the left turn signal is black-white and the right is black-green. What many people don't know is that the rear turn signals are not fused. They are connected directly to fuse 9 and 10 of the 10-pole fuse box (upper side), together with the supply wires from the main harness. On the other side, the front harness is connected.
The 1987 911 has two wires on both sides. The main harness is connected on both sides (it also includes the hazard light wiring). I assume that something is shorted in the front for both cars.

[zuch]

Disconnect each wire from the fuse panel. Measure resistance from the battery ground and the wire you just removed. Should be a couple of ohms if the bulb is in place. It should be infinite (OL) if the bulb is removed. If one wire reads 0 ohms, you have found the one with the short. Check the bulb housing on that wire.

[PopsRacer]

the wiring for the indicators and parking lights on the US cars runs through the headlight bucket. There’s a 3-way plastic spade connector in there.
Was there a headlight conversion or other change up front at any point? If you flip the wires for the signal filament and the parking lamp filament (for ex) the signals will work with the lights off but not with the lights on. There are probably variations on that theme.
If the bulbs are not oriented correctly you can have issues with them lighting - and they will go in 2 different ways.
I would pull the bulbs out first and check the voltages first. Turn on the lights and measure from the contacts that touch the bottom of the bulb for each condition.
If you are not getting power to the right contacts, then (disconnect the battery &) check continuity back to the bottom of the fuse panel.

If the hazards work then your flasher unit is fine. It’s the same module for both functions.

Definitely check the wiring to the fuse panel, it sounds like it’s been messed with. Sometimes wires also get pulled out when owners fit the covers back on.

Here is the bit of the fuse panel from the 87 model. The wire colors are abbreviated in German but are easy to pick up. (S = black, etc) the bottom of the diagram is the top of the panel, the top of the diagram is where the wires run to their systems.

[Undecided]

Update on my '77: (I'm the partner)

Low beam solution: low beam wire became unplugged when reassembling the lower dash

Luggage compartment light and clock: Jacqui (CarmenCarrera OP) used a couple of wiring diagrams to isolate the constant hot wire on the light switch and it looks like the alligator clip was exposed shorting on something. Wrapped in electrical tape and problem solved.

Rear Left indicator: after fixing the above two things we put the third wire back at the top of the fuse and I have all left rear bulbs acting an indicator when the lights are off, but steady bright light when lights are on. Right now, I'm just happy to have a rear indicator with the lights off. We'll have to figure out why it doesn't work with the lights on.

[carmencarerra]

Originally Posted by zuch

Disconnect each wire from the fuse panel. Measure resistance from the battery ground and the wire you just removed. Should be a couple of ohms if the bulb is in place. It should be infinite (OL) if the bulb is removed. If one wire reads 0 ohms, you have found the one with the short. Check the bulb housing on that wire.

Thank you! Got the 77 fixed and will work on the 87 tonight!

[carmencarerra]

Originally Posted by gerakroo

For the 1977 car, the left turn signal is black-white and the right is black-green. What many people don't know is that the rear turn signals are not fused. They are connected directly to fuse 9 and 10 of the 10-pole fuse box (upper side), together with the supply wires from the main harness. On the other side, the front harness is connected.
The 1987 911 has two wires on both sides. The main harness is connected on both sides (it also includes the hazard light wiring). I assume that something is shorted in the front for both cars.

Thank you! Knowing that rear turn signals were not fused for the 77 really helped us diagnose. We have it working now except when the headlights are on. When the headlights are off, the sidemarker light flashes as well. Any idea on what to try to get it working when the headlights are on?

[zuch]

I had a similar problem on my 1964 356C. In that case, the issue was that there were some cars with a single wire system and others that had a two wire system to the same bulb (a dual filament bulb in that case). If I remember correctly, in my case, it was brake and running light (on with headlight). If the car was wired with a single wire, that bulb could only be used for one purpose. If you had two wires and a dual filament bulb you could use the same bulb for both functions by turning on different filaments for the different functions (it would get brighter when you pressed the brake because both filaments would be on). The moral of this story is that you may have some strange wiring at your taillight or a single filament bulb in a dual filament "hole". I don't have a 77 wiring diagram in front of me so I don't know what the stock wiring looks like. My suggestion is to remove the taillight lens and watch which bulb flashes when the turn signal is applied. Take that bulb out and see if it is a single or dual filament bulb. Next, you need to see if there are one or two wires running to that "hole". If you have two wires and a single filament bulb, that is your problem. Switch to a dual filament bulb. If you have a two filament bulb and two wires, you may need to use a volt meter and probe inside the opening to see if there is a short from wire 1 (turn signal) to wire 2 (running light). If you have a single filament bulb and a single wire, you have a short between the running light system and the turn signal system. I hope this makes sense. Let us know what you find.

[PopsRacer]

if the leads for the lower wattage filament and higher wattage filament get swapped the signals will work with the lights off - but not with them on. It sounds like you might just need to flip those 2 wires.