Ok, so I got an overzealous installer that thinks he knows everything but just knows enough to be dangerous. So anyway, he hooked up an alarm and decided to not pay attention to the fact that the parking lights are negative through a resistor and just sent 12v to the wire. All I got from the phone call was that the turn signals are messed up. Is it safe to say that a new headlight switch will need to ordered or any other thoughts as to what is wrong with it.
My guess is "no" you won't have to change the switch.
Multiplexed wires which lower the voltage/current through resistors are in reality pull-down. It's pretty obvious that they need to be pulled down from a higher voltage. In most cases they read 8 to 12 volts at rest. I don't have a car to test the "rest state" so it's an assumption.
Let's just hope he didn't tap into the CAN wires which are 3.5 volts max.
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Prepare your future. It wasn't the lack of stones that killed the stone age.
burns25:
Make sure you lecture your installer about attitude......and a multimeter! 
And reading a tech sheet.
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Oh yeah he got a good lecture for sure. I actually got to look at the car today and it seems he hooked up the parking light wire from the alarm to an ORANGE / green wire at the light switch. At least I think it was ORANGE / green the mind is going with age. The wire tests 12v when the switch is turned on to parking lights and headlights, what it goes to good question. The left turn signal will only come on for the front and the right will work only on the rear and the front left headlight won't turn on. I did get the high beam to work, but what he did I don't know.
Here's my contribution: Chrysler 300 Lights
It's the complete Mitchell for parklights / headlights / courtesy. It'll help you diagnose and trace.
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Prepare your future. It wasn't the lack of stones that killed the stone age.