Drilling through firewall??
 

Was thinking about installing a boost gauge in my 1995 S-350 diesel and would like to know the best way to route the hose. I am kinda leary of drilling a hole through the firewall as good as Mercedes has the interior sealed off. Don't want a lot of air or road noise coming through. Any ideas??

If the hose is long enough you can try to pass it through the rubber gromet together with the electrical wires behind the glovebox, otherwise choose another factory installed wire or cable (such as the throttle) that goes through the firewall and see if you can squeeze the hose through the same hole. If you can not, then drill a small hole next to the one that the wire or cable you selected goes through. When you are done get some silicon and spread it around the hole that you drilled (after you pass the hose through, of course) so that you can seal out any water from entering the interior. Do not drill through the floor because it consists of two layers spaced about 3 inches apart.

Good suggestion
 

I am very against drilling into firewalls unless as a last resort. Try looking through the glovebox or the drivers' panel as suggested.

An alarm installation company drilled through the firewall of my old 190E, right into the power brake booster! They didn't make any money on that job.