Thanks for taking the time to read this. I have a 2012 Gl350. I am having some electrical problems. I purchased the car being told it needed the accessory battery. There are multiple electric things happing that i was told the battery would solve. Such as parking lights staying on after the truck is shut off and locked, codes being thrown, windows not working properly etc. This caused me to disconnect the negative terminal and leave that off over night. Overnight we had a large rain. I went to the truck this morning to reconnect the battery to use for the day until I can get it to a shop. When I went to reconnect I notice the battery compartment was full of water. Obviously there are more issues than just the accessory battery and I was curious if this could be the root of the problem and not the battery. Maybe the battery doesn't need replaced and we need to figure out where this water is coming from. I have already checked and looked into the vent mounted to the fire wall to make sure it is clear of debris. I had read online that that usually causes the problem and they tend to leak if this is clogged. It was completely clear and was not the issue. Any further advice or recommendations of what to check will be greatly apricated. Thanks!

 

Yep the water is the root cause of your problems and I would dump this truck right now. Depending upon how long this has been going on you could have irreparable corrosion damage to vital electrical control modules and be in for a repair bill more than the car is worth.

These are two ways water gets into the battery compartment under the passenger seat:

1. There is a clogged drain in the cabin air filter box on the passenger side of the firewall, and when it fills up the water flows over the cabin air filters and drips into the passenger footwell. You mentioned checking a vent, but not popping the cover box off and checking the drain at the bottom of the compartment, If your air filters are wet this is the culprit.
2. More rare, but a leak or break in the sunroof drains in the b-pillar.

Also look for water in the spare tire well in the back. These are two ways water gets into this compartment:
1. Through cracks or gaps in the third row sunroof, drips down the d-pillar and pools in the bottom.
2. Through faulty taillight seals.

 

Yes, it sounds like you have the characteristic leak on the W/X164 platform. Search this section of the site, it is extensively discussed.

Root cause appears to be leaking taillamp gaskets, which are replaceable.

Source of myriad electrical problems seems to be corrosion in the rear SAM caused by leaking taillamp gaskets. Some people report cleaning the SAM and reusing it, others replace the SAM.

 

Yes, the rear sunroof does have tendency to leak too.

 

Thanks for all the info. After my search, I found the rear drivers side taillamp very loose. All 3 bolts from the inside were almost off. Found water in the rear drivers side well and the middle compartment (no spare tire but where the adblue tank is) I have been drying and parking in garage. Every time I drive it water reappears in these area's. I have not drove it in rain, wet conditions or anything. I continue to dry as much as I can every time and try to find the root of the problem, where the water is coming from. I just took another drive and no water at all. I think it may have been the tail light and there must have been residual water from the that may have just appeared from the vehicle moving. Any thought on this would be appreciated. As far as the electrical problems. There is only one thing not working right. My right turn signal will not turn off. Solid yellow light even when the car is off and locked and my SRS light. Does this have something to do with the SAM? If so is that the electrical box in the middle rear compartment on drivers side? Any thing I should try as far as cleaning it and maybe reusing it. If this is not my problem does anyone know what's going on with the turn signal?