So all my turn signals work perfectly fine when my headlights and/or running lights are off. They're all normally lit and blink as supposed to until i turn on the running lights and/or headlights, the blinking speed decreases. The signal stays on for about 3 seconds until it blinks. Now recently i found out that when i turn on the defroster, the blinker now is even slower to the point where it sometimes doesn't even blink at all. Anyone know what the issue is?

 

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it sounds like you have an incredible voltage drop, when you start putting demand on the feed circuit, everything else doesnt get as much as it needs/wants. I would suggest looking for loose connections by wiggling. This could be a foretelling of something about to go wrong. If all else fails, upgrade battery cables, look at innovative wiring llc. online