Right turn signals don't work. when park lights are on nothing happens but when park lights are off the right turn signal flashes all the park lights

Possibly bad ground connection - G100
In back of the right headlamp on the frame. Headlamps, turn signals, parking lamp for the right all ground at that point. Corrosion in the wire, broken park lamp wire.
Headlamps, turn signals, parking lamp all have their own ground wire that connects at that point.

Hooking up a professional grade scan tool an check for DTC'S - diagnostic trouble codes in the BCM - body control module may point in a diagnostic direction.

DTC B3949: Right Front Turn Signal
Right Front Park/Turn Signal Inoperative

Circuit/System Description
The Body Control Module (BCM) controls the turn signals based on an input from the turn signal switch, part of the multifunction turn signal lever. The BCM receives an input from one of two signal circuits to determine which turn signal function is requested. When the turn signal lever is placed in the LEFT position, the left turn signal switch signal circuit is grounded indicating that left turn signal operation is requested. When the turn signal lever is placed in the RIGHT position, the right turn signal switch signal circuit is grounded indicating that right turn signal operation is requested.
When a turn signal input is received from the turn signal switch, the BCM will activate the appropriate turn signals. The BCM pulses voltage to the applicable turn signals via the turn signal lamp supply voltage circuits, illuminating the required turn signal lamps.

B3949
A short to voltage, short to ground, or an open/high resistance is seen on the right front turn signal lamp supply voltage circuit.

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Do you tow a trailer? If so check the trailer light plug to see if any of the wires are touching.

In the diagram for rear lamp, the top wires are voltage, the bottom black wire is ground. The brown wire on either side should be tail lamps, goes hot when you turn on the headlamp switch. The other top wire on either should be for turn signal. With everything turned on, is there voltage on that wire?
Because the front works and the rear don't, possible wiring circuit problem? The voltage for turn signals comes from bcm. The bcm knows when you turn on turn signal switch, either side, then the bcm sends voltage to turn signal lamp at the rear and front.

Well, you're dealing with a short. If the right turn signal only works the right side bulbs, you know you're issue must be in the switch. The only way left turn signal would light the right side, but the right signal would not light the left is if you added a diode, which I doubt is the case. So the switch itself is suspect. That or a wiring issue. If you just bought the truck, and this is an existing issue I'd suspect wiring. If it just started doing this I'd suspect the switch.


I would check to make sure someone didn't monkey with the wires and switch the left turn signal with the hazard lights or something (do your hazard lights happen to flash only the left turn signals?). If it has or had an aftermarket alarm you need to check their work and see what may be screwed up. Alarm systems often tap into the parking lights, which will look like all 4 turn signals, but are actually dimmer filaments. Flashing the parking lights would actually make your radio flash too, so I'm kind of leaning this way. Can't say for sure on limited information though.

did you check the directional switch. sounds like you have a bad one

Sounds like a ground problem to me. Bulbs are not getting there ground to complete the circuit so they backfed through the other bulbs.

I would check your headlight relay switch that is located in your steering colum

May want to check the bulbs on the trailer to ensure the connections are solid and the wiring is in tack. May be a weak ground wire connection.

possible bad ground to the lights and it would cause this problem may have happen when gas thank was replaced