I have never used a motorhome. If I want to tow a trailer, do I need to buy a brake controller separately? How to choose the driving mode? Thank you so much for answering my question

No, no factory installed electric trailer brake controller. Read the W/X166 sections for a lot of good info on this. I haven’t seen it come up too much yet in the V/X167 sections.

No brake controller pre- installed but if you have the tow package it has the connections for it if you have the correct adapter. The X167 knows when a trailer is plugged in so it automatically selects/deactivates the driving features for towing. Here are a couple of threads on the subject for this model.
https://mbworld.org/forums/gls-class...ake+controller
https://mbworld.org/forums/gle-class...ake+controller

1. If you have Factory Installed Hitch THEN you have trailer pre-wiring connected to the GLS safety systems

2. Frankly - having a Wireless Brake Controller is much easier than Wired Brake Controller

3. You can check with your MB dealer - however "most" MB dealers do not have significant trailer experience - so you might want to find a Tow/Trailer expert in your area

mikecheng - I have an '18 GLS450 and had a Tekonsha brand wireless brake control unit installed and it worked perfectly. No wire splicing into the MB. The hand held unit plugs into the cig lighter for power and you can "dial in" the amount of brake force you want. It essentially is an accelerometer that senses you are braking the vehicle and then it sends the signal to brake the trailer accordingly - you can adjust the force or level of braking with the handheld unit. A local tow / trailer place did the install for me. Good Luck.

A couple of points here.
There is no "splicing into" the car to use a wired controller, there's a socket in by the driver's footwell that you just plug into. You just need an adapter that you can make. When I get home I'll edit this post to add an M-B tech bulletin with parts numbers and directions. About $7. I understand that e-Trailer sells one too.

I vote for the Prodigy RF, I have used the P3 and the RF. That RF works better.
But the accelerometer is located on the trailer, not the Hand held unit, which is one reason it works better, especially at low speeds, like refueling.

I strap my hand held unit to the grab handles on the center console, so it's right at hand for manual brake application. You don't have to fumble around for something hidden in front of your knee.

Talking to the Tekonsha engineers, they say the RF is the best performing controller in their lineup.

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Thanks all for guiding me to driver comparment plug in.
Most trailer brake controllers (RF or Hard wire) need 30 amps of +12V power via a 10 or 12 gauge copper wire from battery with adaquate circuit breaker protection.
MB supplied 180 watts (15 amps) to terminal 4 of the 7 wire round receptical for trailer pigtail.
How did you wire new 30 amp power to contoller and then to trailer receptical for pigtail ?

I have installed a Prodigy P2 controller. I have 2 axles with brakes and each wheel has a magnet capable of 3 amps each so I think we are only at 12 amp draw so in my case 15 amps is plenty. I have had similar setups for years without any problems.

So you get better mileage NOT using strong regen? When you say intelligent regen, do you mean you simple use comfort mode or just put the car in DRIVE when you start out?

Ignore my last postl obv meant for another thread