I have searched and seams this is a common issue with different causes. I have determined is fuse 18 will blow with either turn signal, hazards, or the brake lights on. It doesn't always blow immediately. Once it blow when I stated the truck with the hazards on. Usually will blow shortly after I start drivinng
I have read it could be the multi-function switch in the steering column or the brake position switch.

I disconnected the tail light harness and the fuse does not blow. I reconnected the harness and removed the stop\turn bulbs and the fuse does not blow. My thinking is if there were a wiring issue with a wire shorted to ground removing the bulb would not change the issue.

Could it be a bad ground (high resistance) causing high current?

Does anyone know where this circuit is grounded?

 

The hazards are on a different fuse (F27), they shouldn't be able to cause F18 to blow.

Fairly unlikely, but not completely impossible.

Also fairly unlikely.

Okay, you're going to have be very specific about what connector you unplugged.

Replace the bulbs.

True.

Ohm's law. High resistance = low current.

Based on the data you provided, it's in one of the bulbs (assuming your reports are accurate).

 

Thanks for the feedback. I found the issue to be the wiring harness for the trailer plug. I removed it and the issue of blowing fuses went away. I found corrosion where the harness plugged into the 7 pin receptacle. Also the 4 pin receptacle was corroded. The harness must have been drawing some current and by adding additional current with the brake/turn bulbs put it over the 20 amp fuse capacity.

 

The factory trailer adapter should prevent a short in the trailer feeds from taking out F18, it's isolated by relays and the trailer turn/stop lamps are fed from a different fuse. The only way the trailer circuits can take out F18 is if they were wired in post-factory or if there's a cross-circuit between the primary and the trailer wiring circuits.