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Suburban turn signal issue

turn signals flash too fast on my 2000 burb–as if a bulb is out, but all bulbs are good, and a new flasher wasn’t the answer either. plug in the trailer, and everything is fine

Are you using LED bulbs? Some don’t include load resistors, so the flasher doesn’t ‘see’ the right circuit load and flashes fast.

Did you replace any bulbs or otherwise do any electrical work on the car just prior to this happening? If not, everything was working fine and this just started happening, and all the turn signal bulbs front, back, side, emergency flashers are a bright as they should be, well, that’s a tough one. My first suspect would be the turn signal switch I guess.

I wonder if there is a bad ground someplace in the body. However, when you connect the trailer, you establish a ground from the trailer through the hitch to the frame of the truck. There should be a ground between the engine block and the body. If the battery negative cable is connected to the engine block, but the engine block to chassis is bad, then I can see how you are getting a better ground through the trailer to the chassis.

In the mid 1970s the joke was that turn signals were an unpopular option on Suburbans and Cadillacs because their drivers rarely bothered to use them.