2000 Blazer 4-door 4x4 LT
My right turn signal blinks fast, the left one normal. Replaced all the bulbs even though they were fine, replaced all 6 rear fixtures even though they were fine, replaced all light fuses. All lights work, both filaments work in the bulbs with two filaments. Hazards work, brights work, fog lights, everything works. When signaling left, on the left rear tail light, both of the upper bulbs blink, whereas only one blinks in the right side tail light. Both upper bulbs get bright when braking on the left, only one gets brighter on the right. Hooking up a trailer and plugging in it's lights to the 4-prong connector on the Blazer, makes the right signal blink normal. I've replaced the 4-prong trailer connector for good measure. Now I'm stuck. This thing has been blinking fast for about 60,000 miles, I'm so sick of it.

Ok I know there are a thousand threads out there on this but I can't find the one I need, so just please bear with me and help! thanks...

 

You have a problem either in the plug on the right side or in the wiring to the right side tail lamp. I have replaced a number of the plugs used at the tail lights in the past. Some can be disassembled, cleaned, and reassembled, but if the corrosion is bad enough, you'll have to replace the whole plug, if that is the problem that is.

A search for "turn+signal+wiring" should turn up a schematic for you to chase the wiring if necessary.

 

Cool, thanks for the help. I'll look into the plug, I really just couldn't think of what else to try. Should know if that was the problem within a couple hours...

 

I'm not sure if I have an old connector laying around that I can dismantle again to show you what to look for, but I can check.

 

Just took a look at the plug, it looks to be in mint condition. Unplugged and plugged it back in a couple times, tried it, problem still there. The prongs inside the plug, both ends, looked perfect, like brand new...

Is it significant that it blinks at the correct speed with trailer lights hooked up?

 

The flasher has a current monitored side for the turn signals to alert you when a bulb goes out. When you add the additional current requirement for the trailer lights, the flasher thinks all of the bulbs are working so it flashes normally. But since you know that one of the bulbs isn't flashing, it isn't seeing enough current when the trailer lights are not on. That part sounds perfectly normal.

Does that bulb blink when the trailer lights are hooked up? If not, then you are going to have to dig into the wiring.

 

Yes. But assuming what Kyle says, the bulb still doesnt flash with trailer hooked up, the problem is with the one bulb socket that doesnt work. You have looked at the socket closely, the problem's not apparent right there.

Now you are going to have to work back from that socket contact.

pull it put a good bulb in, and turn blinker on, wiggle the wires into the socket. No change then start unwrapping the harness while wiggling. I'm thinking you wont have to go too far to find the problem.

Actually, as a short cut, first go to adjacent socket and wiggle the wires going it.

 

Wait a second, the problem is that the right signal blinks fast, it still blinks, but fast. And on the left rear, something's a little screwy too as both the top and middle bulbs blink for the left signal. The top and middle bulbs on the left also both get brighter for the brakes. It has a fast blinking right signal...that's the main mystery. This may be a job for the Hardly Boys.

So if it's sensing it doesn't have enough current, shouldn't that mean a bulb or socket is dead? But there's no dead anything...there wasn't anything visibly dead in the first place, I just replaced all bulbs sockets and fuses to make sure.

 

That's the problem. Both bulbs are SUPPOSED to blink for the right turn signal and get bright for the brake light. It isn't supposed to be just the one. You have identified the problem, now you have to figure out the cause.

 

Let's re-verify that

You said all four bulbs are good but only three light in their respective sockets and all four sockets look good..

I troubleshot the exact problem in a 1500 van last year. It was a corroded crimp in a socket terminal found with the 'wiggle test'

Like I said, start at the socket and work your way up the harness.