Try to locate all ground points 10-20+/- where elect. systems ground to body. May be a brown wires bolted to fender well under hood, etc. Clean them to improve grounding. I have tighten them or wire brushed them and even spraid hard to get to ones with battery terminal cleaner. Also, replace all fuses with fresh ones even if old ones seem ok. Read manual on how to sync. windows, moon roof, and seats.

Hope this works it has for me on 1998 CLK that sat for two years in my 86 year old dad's garage

Rick