[T3] Turn signal help after Bentley test

[Jim Adney]

On 14 Oct 2013 at 22:25, Jacob Adam Schroeder wrote:

> I am having a hard time debugging the turn signals on my 1972 Squareback.
> 
> My problem:
> Left turn signal blinks slow (once) then the fast blink.  Right turn signal
> blinks as it should.  If I turn on the headlights, however, the right turn
> signal will switch to the fast blink.

The fast blink indicates that the circuit is not drawing the expected 
amount of current. Usually this means a burned out bulb. The 
headlight affecting this indicates that the ground for those lights 
is not good. The ground goes to a screw under the cardboard at the 
front corner of the trunk, next to the front corner of the gas tank. 
Loosen that screw, clean it a bit, put some grease on it to slow down 
future corrosion, and retighten. While you're at it, do this on both 
sides.  

> I performed the test in Bentley (with key off, connecting +49 terminal of
> emergency flasher to terminal 30 of fuse box and test turn signals) and
> both left and right work perfectly, at the correct speed, regardless of
> whether my headlights are on or off.  According to Bentley, this means my
> switch and relay are OK.

I wasn't familiar with this test, but notice that the next sentence 
in the bentley says to check the switch if the TSs still do not work.

The test I generally do is to check operation with the 4 way flasher. 
If all the bulbs light equally bright (test at night is best) then 
the bulbs, wiring and relay are okay. That just leaves the TS switch 
as the possible problem. If the headlights affect the test, the front 
grounds are the problem.

If you do my test at night, I think you'll find that the RF TS bulb 
is dim, or maybe it just goes out completely when you turn the 
headlights on (or the R headlight flickers in time with the TS relay, 
and the RF TS bulb flashes out of phase with the RR bulb.)

What's happening is that the headlight filaments are acting as a 
ground pathway for the RF TS bulb, when the headlights are off. But 
when you turn the headlights on, that path no longer leads to ground.

There are also grounds for the rear bulbs, that I think you have to 
remove the rear light bases to get to, but those grounds don't 
usually give trouble.

> What is left?  Presumably it is wiring, but what am I bypassing by directly
> connecting +49 of the relay to terminal 30 of the fuse box?  Why can't this
> be a permanent fix?

The + terminal normally gets power from the 4 way flasher switch, 
from different sources depending on that switch position. The allows 
that circuit to be off when the key is off, unless you pull out the 4 
way flasher switch. Bypassing this permanently could lead to a 
"surprise" at some future point when you're troubleshooting and not 
expecting that circuit to be hot. It could also lead to a dead 
battery if something when wrong with that circuit when the car was 
parked.

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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