Trailer brakes and auxiliary transmission cooler

Hello all,

Yes I did search for the items listed in the subject but I couldn't quite find what I was looking for. Hopefully you kind folks can help. Am I correct when I say that the power administered to trailer brakes comes from the battery? I ask because I'm curious about adding brakes to my trailer and a brake controller to my 240. When I tow with the car now the little "brake lights aren't working" icon on the dashboard is illuminated. The brake lights are working on the car and the trailer. Makes me think the extra draw from the trailer lights make my car think the lights aren't working. So If I add a brake controller and trailer brakes is it possible that the battery won't have enough juice to actually power the trailer brakes? If so then can I just install a battery with more amperage? Or is that a bad idea? I don't know squat about electrics.

Also I read on this forum that if you tow with an automatic transmission then you should have an auxiliary transmission cooler. I can't find one specifically available for a 240 but there are plenty of universal radiators for around 70 bucks. That shouldn't be a difficult thing for a pro to install, right?

Thanks for your help!

Brake light sensor works by detecting an imbalance in the current draw between the brake lights on each side. if light only comes on when towing, someone probably just wired the brake lights to one side of your car. Not a big deal.

Trailer brakes... if electric, yes will be powered by car's electrical system. Battery and alternator should usually be sufficient and any upgrades there would not be harmful to the rest of the car. If you have a particular brake system in mind we could look at the specifications and tell you more.

Transmission cooler - Light loads should be OK without one (the stock radiator handles normal transmission cooling). If you are putting a lot of load and slip into the torque converter with heavy towing, a cooler may indeed be in order to extend transmission fluid life. There is a OEM one which should be available from Wanted section, or loads of aftermarket ones which a competent should could install. Getting a temperature sensor in there too might be nice.

Again, more info about your use case might be helpful here.

Also never tow in 4th / overdrive, use the little lockout button on the shifter to disengage it.