My left turn signal on my 1998 Honda Civic just started blinking really, really fast, or really, really slow… I can’t find a pattern between the two, sometimes it’s fast, sometimes it’s slow, and it will alternate within the same trip in the car. The right turn signal is just fine. I’ve checked out all the lights on the car, and can’t find any front or rear external lights that are blown. Does anyone have any ideas of what may be causing this?
You said you checked out the lights. Did you replace the left front and rear bulbs to make sure they are good?
There may be a bad ground in one socket, possibly there is a a fault in the multi-function switch.(turn signal stalk)
swap out the “turn signal flasher” relay. it should cost about 7 or 10 bucks.
its located in the “fuse” panel, which is typically near your left knee, or ankle in the dirvers space, or possibly under the hood.
if this doesnt fix it, then you will have to replace all the bulbs one by one to find the bad one(s)
My guess is you have combined brake and turn signal lamps in the back. Try replacing the left rear lamp and that should do it. While you are at it, you may want to replace the right side as well since you likely bought two lamps in the blister package and it is likely also getting tired.
If that is not it, locate the flasher by listening for the clicks and replace that. Both are cheap fixes.
Good Luck