My 05 Grand Caravan left (driver) front turn signal flashes more rapidly and less brightly than all others. I changed to a new bulb and even switched the right bulb housing with the left, and it doesn't change. All other bulbs and emergency flasher system works normally. What could this be?

 

You've eliminated the usual culprits. That leaves everything from the light assembly connector to the turn sig switch meaning the connections, wiring and components (BCM and switch). Are you saying the left front works fine with the hazards on?

 

Flashers work fine, and I know the light assembly connector isn't at fault because I switched the right one to the left and problem persists. Where is the BCM?
I also must clarify- Front left turn signal goes on but blinks more rapidly and less brightly than right one. With emergency flashers on bulb still blinks , but much less brightly. All other bulbs work fine.

 

Sounds like a bad ground to me.,....jack

 

Any idea how I go about trying to fix that ground problem or where the most likely ground trouble would be?

 

Using an ohmmeter connect the leads to pin 3 at the light connector and any good ground. Shouldn't see more than one ohm. Compare readings at the right light connector if need be. BTW - pin 1 is turn signal power and pin 2 is park lamp power.

The BCM is mounted on the firewall above and left of the brake pedal.

Probably turn out to be a minor point but swapping light assemblies and having the same problem remain does not eliminate the light wire harness connector. That connector is still in the left light circuit regardless of which light assembly you have connected. It could be corroded internally from road salt or moisture or a pin crimp could be bad creating high resistance. Might try cleaning with contact cleaner then give each wire a slight tug at the back side.