Question about wiring marker light/turn signal

Sounds like crossed wire(s) and/or a faulty or (probably) missing or faulty ground. There are two filaments in each bulb. Bright for turn, dim for parking. There are two base contacts on the bottom of each bulb; one of them is the feed for the bright and one is the feed for the dim. Both filaments ground through the metal shell of the bulb base. If the ground is no good, the bright filament will ground through the dim filament. Result will be turn signal dimmer than it should be, with slow rise from off to on, and often an improper flash rate. When you turn on the parking lamps, then the dim filaments are no longer a path to ground and then the signal won't work at all. So, make sure you've got a good ground at both front park/turn bulbs.