weird turn signal issue (Porsche 924)

When driving my 88 924S, when I go to signal left, initially the signal goes normal speed but within a few flashes it speeds up to double-speed.

- right side signal is normal

- i've tried multiple relays, no change

- all bulbs are working and equal brightness to each other left vs. right.

- when hazard is on, both sides flash normally

- when ignition is off (in ACC), the left turn signal flashes normally. The "fast flash" only happens when the car is running.

Not that it's a big deal, but it's just a little bit annoying, and I can't think of any other reason this would be happening other than relay or bulbs. The part where it only happens when the engine is running (and not in ACC) is the oddest part.

Any thoughts?

Thinking through this: a fast flash happens if a bulb is burned out, ie greater resistance in the system. So maybe you have a questionable ground somewhere?

If that thinking is wrong someone correct me. 

That was my first thought as well, but all of the signals flash with full brightness and no flickering or anything indicating a ground issue.

In reply to spandak :

I think you're on the right path. Some sort of signal issue.

In reply to spandak :

Makes sense to me; that or just iffy sockets or bulbs. I'm wondering if something is right on the brink, and with the little extra voltage of running vs ACC it gets hot enough to go over the edge into "fast blink" mode?

It sounds very Rube Goldberg; I'd probably try different bulbs, or swapping them left for right (and having a scrub at the contacts) if it's not too big a pain to try it out.

I can't think of any *other* reason for it to go into fast mode than the system thinking it's got a dead bulb.

I had a similar problem on my 76 911. Had to rebuild the tail lights. 

markwemple said:

I had a similar problem on my 76 911. Had to rebuild the tail lights. 

hmm, just remembered I have my old taillight assemblies sitting around someplace (had some cracks). Maybe I'll switch out the guts with the new ones and see what happens

My thought was also ground related, but thinking maybe there is an engine to chassis ground that is getting noise caused by the vibration of the engine due to corrosion or being loose?

In reply to EastCoastMojo :

That was my next thought but I didn’t want to go too far down the rabbit hole. 

Swapping stuff side to side should help narrow it down to a component or the harness. 

Theres no change in brightness of the bulbs when this happens? 

True. That type of ground fault would likely cause other issues and not limit the fast blink to just the one side. Maybe some moisture got inside the bulb socket, or the filament is >< this close to failing but hasn't yet. 

Just swapped out one of my old taillight assemblies, with a brand-new bulb, and same problem. This is really odd, since literally everything else works perfectly lighting-wise (even the "side park" lights when the car is off). Not sure how ground could be the issue, since the whole light assembly has a common ground that appears to be in good shape and is connected to a clean chassis ground - and again, all the other lights work fine, and the signal flashes regular speed when hazards are on...

Grounds that appear to be fine sometimes aren't. When the hazards are on, the other side is included in the circuit and that ground may have a better connection.  Have you checked both front and rear turn signal grounds on the left side? And by check I mean removing the wire and cleaning the connector and the chassis contact points?

Have you checked the connections on the front and side turn signal lights?

It’s probably the turn signal switch, they are known for failing and causing weird issues.

Chk the bulb type. You may have the wrong bulb with a different wattage on one side. 

With the wrong bulb it will draw more amps ant that will heat up the flasher causing it to not cool properly or enough. This will cause the blinker to speed up as the flasher heats up. The flasher then stabilizes at a faster rate proportional to the amperage draw. 

Second and equally possible problem is a bad/poor connection in the turn signal circuit as the poor connection heats up it expands worsening the connection  and increasing the resistance. This increases the amp draw in the circuit and once again causes the flasher to increase it speed. This will then stabilize once the flash rate and amp draw and the temperature of the poor connection stabilize as the connection cools while the circuit is open due the the flasher. 

Stefan said:

It’s probably the turn signal switch, they are known for failing and causing weird issues.

it was brand new a month ago...

dean1484 said:

Chk the bulb type. You may have the wrong bulb with a different wattage on one side. 

With the wrong bulb it will draw more amps ant that will heat up the flasher causing it to not cool properly or enough. This will cause the blinker to speed up as the flasher heats up. The flasher then stabilizes at a faster rate proportional to the amperage draw. 

Second and equally possible problem is a bad/poor connection in the turn signal circuit as the poor connection heats up it expands worsening the connection  and increasing the resistance. This increases the amp draw in the circuit and once again causes the flasher to increase it speed. This will then stabilize once the flash rate and amp draw and the temperature of the poor connection stabilize as the connection cools while the circuit is open due the the flasher. 

Yeah, I'll verify that all the bulbs match tomorrow, but IIRC I replaced them all from the same package when I put this car together, so they should all be the same. Swapping various bulbs in had no effect on anything, anyhow. Guess it's time to chase wires or simply live with a stupid fast signal, lol.

EastCoastMojo said:

Grounds that appear to be fine sometimes aren't. When the hazards are on, the other side is included in the circuit and that ground may have a better connection.  Have you checked both front and rear turn signal grounds on the left side? And by check I mean removing the wire and cleaning the connector and the chassis contact points?

Yeah, that's on the lsit to check tomorrow. When I put the car together I cleaned all the grounds well, so seems unlikely to be the issue, but who knows, maybe something came loose. Curious that this just started in the last few weeks though. The car has basically just been sitting in the garage for the most part.

When I rebuilt mine, I used new sockets and had the old machines out. Created all new contact points for positive and earth.

markwemple said:

When I rebuilt mine, I used new sockets and had the old machines out. Created all new contact points for positive and earth.

that makes sense, but still seems unlikely that BOTH of the assemblies i have both have the same problem, just with that one socket. When I put this nicer set in, I cleaned all the contact points well at the time. I think the place to start is gonna have to be the ground and ground wire in the harness/plug.

You have an ohm meter?  I would start testing things.