So my driver side tail light will turn on with lights on but when applying the brake, only the passenger side and 3rd light will light up. When applying the alarm the driver's side will also flash like the passenger side. This is on a new brake switch. Any ideas what it may be?

 

Have you replaced the brake light/tail light bulb?
It's one bulb with two filaments, so the tail light may work while the brake light
filament is burned out.

 

Gotcha, I'll give that a try and report back.

 

What year car?

The brake lights are completely separate circuits from the running (tail) lights. No light bulbs after 2003, they're all LEDs which should outlast the car. On the '03 and earlier there are separate light bulbs for running and brake lights -- no dual filament bulbs. Since 2 our of 3 brake lights are illuminating my guess is a bad bulb if you have an AP1.

-- Chuck

 

While I have never changed a bulb in my AP1, the wiring diagram and parts diagram both appear to
show a dual-filament bulb for the brake/taillight

 

So I bought the bulb and when I went to change it I remembered the previous owner had a sub box built on that side. Didn't want to deal with it this late so I'll have to tackle it tomorrow after work. Car is 2001 by the way.

 

You're right.

The wiring diagram for the '00-'03 cars shows a 21w bulb for brake and 5w for running. Circuits are on different pages in the shop manual so it looked like two different bulbs to me. Turns out they're part of a dual filament bulb. '04 and later show LED.

-- Chuck