I did a lot of searching on this site, & didn't come up with a complete solution, so I expanded my search to the 'Net. It seems that the safe thing to do is to replace the non-flashing bulbs. If you replace the flashing bulbs you encounter a condition known as hyper-flashing because of lack of resistance in the circuit. There are workarounds involving splicing resistors into the circuit, but I really didn't want to do that. One theory that I came up with is a simple plug n play solution at the rear bulb holder assembly. I traced the path for the turn signal to a female connector on the backside of the bulb holder assembly. The male VW connector is available, so attaching a resistor across the turn signal & ground should make a neat & easily reversible fix, but I never got around to testing the theory. YMMV. The other issue is heat coming off of the resistor heat sink melting plastic, another thing I didn't want to deal with. The resistors need to be mounted away from anything they could possibly melt.
In the image below 31 is the ground & BL is the blinker.
I took a gamble, & if it had failed it wouldn't be the first time on this VW. LOL The cost would have been buying a replacement switch. There isn't a normal flasher relay to deal with in the fuse panel. The flasher & hazard function are part of the actual hazard switch. I pulled the hazard switch out & carefully removed the outer casing. In the image below there is an IC that reads resistance & causes hyper-flash if a factory style incandescent bulb is out, or if a LED bulb with too little resistance is in the circuit. Cutting pin #7 stops that function. I used a dental pick & carefully leveraged the circuit at pin #7 apart. It's a tight fit. There also is a fix for the flashing rate, but it would involve stripping the switch down to get at pins #4 & #5 to change the resistance there. What happens when cutting pin #7 is that while not exactly like a factory flash rate, it's slightly quicker, but it won't hyper-flash anymore.
This is the fully outfitted rear bulb assembly. There is one mod that needs to be done to the back-up bulb hole in the actual taillight. The hole is "D" shaded. I used an X-Acto knife To make the flat part of the "D" slightly rounder. It doesn't take much material removal to make the new bulb fit. I spent about a minute whittling away, mostly to keep the blade from snapping, & then 5-10 seconds with a shop vac removing what fell into the hole.
The difference in LED color between Warm White & Cool White. I used Warm White behind the colored lenses, & Cool White behind the back-up lights.
As for how bright they are, they are bright. These specific LED's are about 95% as bright as incandescent, & will continue to radiate 360° for their life time. You get what you pay for. The incandescent brake bulbs I pulled no longer did so. They blacked out a good portion of the glass, ala 1970's cube flashes, & the outside of the glass was a mirror that light no longer passed through, changing the output pattern.
In the image below 31 is the ground & BL is the blinker.
I took a gamble, & if it had failed it wouldn't be the first time on this VW. LOL The cost would have been buying a replacement switch. There isn't a normal flasher relay to deal with in the fuse panel. The flasher & hazard function are part of the actual hazard switch. I pulled the hazard switch out & carefully removed the outer casing. In the image below there is an IC that reads resistance & causes hyper-flash if a factory style incandescent bulb is out, or if a LED bulb with too little resistance is in the circuit. Cutting pin #7 stops that function. I used a dental pick & carefully leveraged the circuit at pin #7 apart. It's a tight fit. There also is a fix for the flashing rate, but it would involve stripping the switch down to get at pins #4 & #5 to change the resistance there. What happens when cutting pin #7 is that while not exactly like a factory flash rate, it's slightly quicker, but it won't hyper-flash anymore.
This is the fully outfitted rear bulb assembly. There is one mod that needs to be done to the back-up bulb hole in the actual taillight. The hole is "D" shaded. I used an X-Acto knife To make the flat part of the "D" slightly rounder. It doesn't take much material removal to make the new bulb fit. I spent about a minute whittling away, mostly to keep the blade from snapping, & then 5-10 seconds with a shop vac removing what fell into the hole.
The difference in LED color between Warm White & Cool White. I used Warm White behind the colored lenses, & Cool White behind the back-up lights.
As for how bright they are, they are bright. These specific LED's are about 95% as bright as incandescent, & will continue to radiate 360° for their life time. You get what you pay for. The incandescent brake bulbs I pulled no longer did so. They blacked out a good portion of the glass, ala 1970's cube flashes, & the outside of the glass was a mirror that light no longer passed through, changing the output pattern.