for several years, I had bullet lights across the front spoiler that worked with the parking lights, and the outer bulbs on each side were tied into the turn signals.
the type of filament in these bulbs didn't stand up well to road use and they were constantly needing replacement.
about 13 years ago I had to swap my front bumper, so I had to remove all the lights and wiring, and never bothered to put it back after.
I couple of years ago I bought LED versions of the same lights and put them on my "to do list" for the van.
well, today was the day.. ran all new wiring, soldered and shrink tubed everything.. only to find it didn't quite work...
with the parking lights on, everything appeared the way I wanted... lights would blink with the signal, etc... but if I turned the parking lights off, they didn't do anything. testing with a regular bulb showed the circuit was doing what it was supposed to.
if I reverse the polarity on the LEDs, they work with the turn signals as long as the parking lights aren't on.. but didn't work at all with the parking lights.
ok.. conundrum time..
I solved the problem by adding a relay on each side..
the pulse from the turn signal/parking light trips the relay, which then feeds 12VDC to the LEDS from the battery, so it's always the correct polarity.
now they work as turn signals if the parking lights are on or off.
I did have two bulbs that didn't work at all, so I used the old filament bulbs till I get the LED replacements in the mail.