Exterior lighting issue

Use a voltmeter at each of the sockets in question to measure across the terminals. With the vehicle running and the light turned on you should see a measurement very close to battery voltage. If you get a reading that is lower than what you measure at the battery by .5v or more then you have a definate problem.

Next take the voltmeter and attach 1 terminal to battery ground and the other terminal to the pin in the lamp socket. If your reading goes up (more volts measure) then you have a ground problem.

Another method that might be somewhat simpler is. Run a piece of wire (temporarily) from the NEGATIVE battery terminal to the ground for the passenger side turn signals ground. If the bulb is no longer "slow and dull" then you have a ground problem. Other likely culprits are dirty/corroded lamp sockets and the infamous bulkhead connector.