When I turn the left signal on, it blinks really fast. But the right one blinks normal. However when I plug the trailer harness in the back, both sides blinks normal. What could be the problem here? what should I check for? PLease advise. thx.

 

Are the left bulbs good on the truck?

 

As fschiola indicated a burnt out bulb will make your flashers go crazy. When you plug your trailer in you added more bulbs to the system and they settled down.

Floyd

 

Check your grounds. Some of the hardest problems to trouble shoot come from no ground to high resistance ground. If that is the case it is like your bulb is burnt out when it is not. A high resistance ground will cause the system to look for a different path to ground. I have fixed several problems concerning grounds and some of the things they cause are really interesting.

 

Thanks for the help. Just a burnt out light bulb. All is good.

I've never would've though a burnt light buld would make the blinker go crazy like that. Had plenty of bad bulbs before but none of the vehicles behaved like this one did.

 

All of my vehicles have done this since I can remember. From a 80 Chevette to my truck now (99) Most of mine have been older but all kinds of different manufacturers

 

I think the abnormal flashing was government mandated in the '90s to warn people they had a bad bulb.

Got me to thinking, I've never replaced any of my bulbs in 16 years and half a million miles on either truck.
Guess the OEMs must be good ones.

 

I thought you might be out of blinker fluid. J/k

 

After much searching I found good source for fluid but now they're even sold out.
Should have some in soon here> http://kalecoauto.com/index.php?main...&products_id=6
Really keeps your flasher syncros lubed well eliminating that annoying clicking noise that most turn signals make.