One side of the gf's pickup has a fast blink, front and back- yes, both ends are functioning, but blinking very quickly.
What the heck? I know that, typically, if one burns out the other will fast blink, but for them both to be working? Any ideas?
It's an 01, if I remember correctly.
Does the front have two turn signal bulbs on each side? One could be out and the other still working.
Yes, side marker bulbs are my guess
Do they still use those electro-mechanical flashers? I always found that when my blinkers blinked fast, the flasher was about to fail. Changing the flasher fixed it.
check light function on the other side and then verify everything on the fast side is coming on. If one isnt change it. If it still blinks fast Id replace the bulbs anyway.
Never had one that only blinked fast on one side not be a bulb.
Turn the Headlights on and try the blinkers.
My theory is that a double filament bulb has just one filament out.
I once had a '83 Rabbit that called for double filament tail lights. One was wrongly replaced with a single filament bulb that caused wierd activity.
Have any bulbs been replaced with led bulbs? This too can cause wierdness
Chronic problem with GM trucks of the era. The sockets are crap. Pull the bulb and you'll probably find all kinds of crusty green goop on the contacts. They also had corrosion around the ground screw for the harness.
Best solution is an aftermarket socket from the Help! section at the auto parts store.
Maybe you'll get lucky and its just a filament, but I'm just warning that you may have additional issues.
Curtis73 (Forum Supporter) said:.......... They also had corrosion around the ground screw for the harness......
Thats what I was going to say , bad grounds can cause all kinds of fun !
Have you checked the Blinker Fluid?. . .. 
Ok I will show myself out. . .
+1 for a ground or corrosion issue.
Some of those trucks have a small 2nd turn signal bulb in the tail light that's easy to miss. Also if it has a trailer wiring harness that could be an issue.
I thought bad bulbs caused a slow blink, and a short would cause a fast blink with older flashers.
So I got in there last night. There was a bulb out beside of the turn signal - replaced it and the lights went normal. Put it all back together and we're back to fast blink.
This was done in her driveway about 7:15pm, so it was getting dark. I'll look at it more later/this weekend. I DID see the green stuff in the socket like mentioned above, and some moisture, tried to wipe it away using Qtips. Again, it worked...for a moment. Not sure if the bulb dislodged as I was putting it back together or what. Again, I'll get back at it later. They are all working so she's safe, just annoyed
You guys are slipping, no one suggested Blinker Fluid?
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