I have just spent a few hours researching this problem and I can find similar issues, but nothing quite as strange as this one. I recently bought a 1999 626 that was well maintained and is in good condition. After a few days I discovered that when my headlights are on and I put on my left signal light every light in the car starts to flash, the headlights, tail lights, stereo, dash, etc. These are all flashing faster than a normal signal light. When my headlights are off this does not happen. I checked the grounds on both sides of the car and had to replace the once on the left due to rust. I thought this would fix the problem and it didn't. If I remove the bulb from the left front signal light the problem goes away. I unplugged the sockets from both front lights and swapped them with no change. I checked the flasher module and it seems fine. As I said it works when the headlights are off. I can not find any damaged wiring anywhere. When I am under the hood with the left signal light and headlights on and ever light flashing in the car I could hear the relays under the hood in the fuse block there flashing. I started pulling them out and replacing them again it all of a sudden stopped. I thought I had it fixed but it started up again. Pulling these relays did not change anything this time. I have had this to a garage now and it is starting to get expensive with no end in sight. Any advice or suggestions? Anyone ever heard of this problem before?

Thanks for the help,
Howard