under-hood contact switch - what's it for?
 

I was replacing my car's monovalve last night (to restore heat to my '91 420SEL - 126 chassis), and noticed a contact switch mounted more or less above the monovalve. This switch is visually the same as the door-jam switches that turn on the dome lights when a door is open. This particular switch operates when the hood is open.

I assumed that it was for an underhood light of some kind, but there is no light visible on my car, and I couldn't find a bulb or socket anywhere. Plus, when I look in various M-B parts catalogs and web sites, I see no reference to either an underhood light, nor to this switch.

Does anyone know what it is for? If it is for a light, where is the bulb supposed to be?

In my 126, this switch is located between the two firewalls, toward the center of the car from the windshield wiper fluid reservoir and battery area. It is also basically just behind the firewall, behind the transmission dip stick, and is mounted on a bracket that also holds a diagnostic port connector (as I said above, just above where the heating system monovalve is).

Thanks for your help! BTW, repairing the mono volve with the monovalve repair kit solved my lack-of-heat problem. Sure enough, the diaphragm on the monovalve piston insert was ripped, leading to highly intermittent operation. Since the monovalve is actually pulsing fairly continuously during most normal heating conditions, a sticking piston resulted in too little heat.

Bob Schleicher
bullswin5@aol.com
1991 420SEL, 174,000 miles

It's part of the anti-theft system.

Anti-marten protection system, applies high voltage shocks to critters in the engine compartment.

Martens are a relative of the weasel, and love to make homes in engine compartments in the winter. They are ferociously territorial, and will rip up each other's "homes" if they detect the smell of another marten in there. They chew up all the plastics, including engine covers, rip heater hoses off, chew off the wireing, and will pull the insulation off the firewall to eliminate the scent of the other marten. Very destructive in Europe.

Foretunatly we don't have them here, but the anti-marten system does help to keep mice out.

Peter

I "think" the first reply was much more accurate..........

Gilly

I think it's un-American to be anti-marten.

thanks for clarifying Gilly - psfred's pretty reliable but I wonderin'... :D

I have to remember not to drink a beverage while reading some of the threads . . . and to buy some monitor wipes tomorrow. :D

If it's part of the anti-theft system, what does it do?

Peter

sound the alarm?

If the hood gets opened while the alarm is set (lets say someone REALLY wants your air cleaner for some reason) then the alarm would go off. I guess this would happen by breaking the window (no glass breakage sensor) and reaching in and pulling the hood release. It does the same thing for the trunk lid, but there is already a switch there for the trunk light, it uses the same switch for anti-theft.
MAN, I've read about anti-Marten, works kind of like an electric fence, and mounts on the under-body panels, ummmmmm, not really seen "much" in the US, probably not in Europe either, but that's a guess.

Gilly

Pretty much standard equipment in Germany, it's a real problem in any area near forest (and most German cities have a decent sized forest in town!). Car get totally trashed the second time one jumps in, I've seen video. They even rip the coolant hoses off.

Peter

psfred - you're not gonna get me this time... :D

This has me thinking. Suppose the hoodlums that steal hood stars are "Martens" and the hood star is what needs the protection? zzzzzzztttt!!!!!
Gilly

Then there is the anti-MARMOT system common to parking lots in the western sierra back packing jump off points. Chicken wire wrapped at ground level around your car. They eat insulation and rubber bits if given the chance. Martens in Europe; marmots in the western U.S......what you gonna do ;)

MPS until about 9/92
 

OK class, those of you who remembered your service manuals please turn to section 0080 of the Electrical Systems chapter. This describes the testing procedure for the MPS (marten protection system). Those of you with cardiac pacemakers are excused. When operating properly the MPS is only activated when the hood is closed (hence the need for the button described at the start of this thead). Persons with cardiac pacemakes should not fool with this button before they have willed their beloved MB to an appropriate heir. Those of you unfortunate MB owners with nearly new (i.e., after 9/92) vehicles, please take care to avoid a marten attack when opening your hood.