Driving in the rain recently in my 2017 TLX, and the brake hold and emergency brake warning lights lit up like a Christmas tree. I had noticed that I had been getting water in the passenger side tail light for some time but never thought much of it. Upon checking, it was just about filled with water. Following advice, I was able to stop water from getting into the tail light by replacing the gasket behind the light and applying some silicone to the gasket and washers. That is the good news.

Bad news is that I just took the car through the car wash and the same lights came on. There is definitely water causing some sort of short as once things dry out (which takes maybe an hour) the warning lights go away. There is a slight musty smell starting in the cabin, but no visible water and nothing damp. I've check the sunroof drains (the two towards the front of the car) and things appear fine - I snaked about 6' worth of string trimmer line with no obstructions. No visible water coming in the trunk but I'm wondering if things are pooling where I can't see; possibly where some brake hold or e-brake wires are?

Water has to be coming in somewhere but I don't know where to check. Any help would be appreciated!

 

Yeah musty => bad! Have you checked under all of your trunk lining? You might try putting down the back seats and having someone peak into the trunk while you go the car wash to see if they notice any water entering. You'll probably want to remove the trunk lining first to ensure nothing is hidden from sight.

 

Check both rear electric brake actuators and associated wiring harnesses - likely a damaged connector or wiring.
Try disconnecting the wiring harness at each actuator, dry it with a hairdryer if it's wet, and pack it with silicone dielectric grease before re-connecting it. This will help restore water proofing and eliminate electrical issues that are likely causing the warning lights. Other possibility is a defective actuator.

 

Thanks for the tips! Where are the rear electric brake actuators? I did some googling it looks like the parking brake actuator is there, but I'm not seeing the brake part. Are they the same?

 

The actuator is just behind the caliper - check this video and it shows it well.