The 4-pin flasher relay I needed for my 1970 van indicators was missing and because of the broken mess of my fusebox and other missing one-year-only difficulties, I changed it to 1973-on, so the original relay wouldn't physically fit.
No worries, I thought; I have a 4-pin flasher relay for a 1973 bus that fits my fusebox.
The problem is that the indicator tell-tales in the T2 dash have an ignition feed and need grounding to illuminate.
But all the 4-pin flasher relays around today (it seems) are designed for tell-tales that are grounded and need 12V to illuminate.
The traditional fix is to use a 3-pin relay, and piggyback the tell-tale lights onto the main flash output, so that the tell-tales illuminate by grounding through the main indicators (obviously when they are in the OFF flash phase).
And there are online VW parts retailers that sell the 4-pin relay for bays with a note to the effect "if the dash tell-tales don't illuminate, connect the blue/red wire to the black/green/white wire" (i.e. use only 3 pins of the 4 pin relay!)
However, grounding the tell-tales through the indicators means they are out-of sync with each other, so that when the hazards are on, you get an alternating red/green flashing effect between the hazard switch and the dash tell-tale.
Dissatisfied with that, and having an electronics-related day-job, I decided to take my black plastic 4-pin relay (DNI 0831) apart to see if it could be adapted. Pins are labelled 31, 49, 49a, KBL. It doesn't work as-is because KBL is a high-side switch for grounded tell-tales.
I was slightly surprised to find it was all surface-mount electronics inside, but I found the NPN emitter-follower KBL output stage and I was able to remove, re-solder and reconfigure it as open-collector (i.e. low-side switch for 12v-fed tell-tales).
Now the KBL pin works as VW intended and tell-tales are in-phase with the indicators and the hazard switch lamp.
Quite why VW decided both tell-tales should be tied together I don't know, and I have seen modification details to make them independent, but I chose to leave mine functioning as originally specified.
Most of the online diagrams I have seen for 4-pin relays have a similar NPN output stage and could therefore probably be modified in a similar fashion.
I can provide more details if anyone's interested, but there's a risk of inducing sleep.
although I don't think I'll bother with trying to re-solder the relay as it works well enough for me. Got to admire your knowledge and perseverance with that though!
