W116 Headlamp Switch Go Boom:

[Doktor Bert]

Recently, my headlamps have been 'lazy' on cold mornings. Tonight on I-10 in Redlands my low beams went out. The switch was hot to the touch and all fuses were intact.

Flash to pass function still worked, but I ran a jumper from the park lamps to the low beams to get the car home.

Where could I get a replacement in So Cal tomorrow?????

[Doktor Bert]

Waiting for first light this morning to drive in to work. I will seek a replacement today....

[charmalu]

I was in the carson city yard last mo and they had 2 116 in the yard. I`ll pull one/both if you want in a couple days when I get there. leaving this morning for there. HMMM...... doesn`t help you now.

Charlie

[scottmcphee]

You can keep your next switch alive forever, by adding a relay to power the lamps rather than running the high current through the headlight switch contacts. Just use the switch to power the relay coil, and move the high current path through the relay contacts.

The problem happens when switch contacts begin to degrade, they increase resistance at the resting point of contact. Increased resistance creates more voltage drop *at that point*, which amounts to power waste (heat) at that point. This cycle keeps up until the switch starts consuming more power than the headlights as you are effectively making a little resistive heater in there. (100 Watts is a lot of heat to balance on this power split between the headlights and switch contact heater - next time you grab a 100W bulb see how long you can hold on!).

Not to mention your headlight voltage is dropping as this carries on over time, getting dimmer and dimmer... even with new bulbs. At some point of wear you'll get a sizzle.. melting plastic, fried contact for sure, some smoke, maybe a little fire, and a switch to replace.

You only need very little current through the switch contacts to power a relay coil. Those contacts are so overkill for switching a small coil, they'll last forever. Even if you don't put a flyback diode or snubber on the coil.

If in your lifetime the relay contact degrade, you can pop a new one of those into its socket for $5, in 1 minute. Versus changing a headlight switch again, that will be harder yet to find.

FYI - I located my relays up hear the headlights to keep the high current run very short, because there's voltage drop between the switch and headlight due to wiring constriction (limits current). And I made a direct power run from battery (fused) to those relays using a very heavy gauge wire (like 10AWG).

Brightest bulbs around! They're getting slightly over-rated voltage this way. Most auto headlight bulbs are rated at 11.7v or so, something lower than battery/charge limits... They do this to accommodate normal wiring constraints and voltage drops just mentioned. Give these bulbs a full shot of just a half volt more than they're expecting and you'll see noticible brightening!

For me, headlights are the most critical safety component for getting to my destination at night, in the winter, at -40C... you don't want to stop anywhere other than a warm garage. Every other electrical thing on my car can stop working for all I care (and this could happen!) so long as the headlights shine and that diesel remains turning over... I'm getting home.

[Doktor Bert]

Charlie,

Thank you very much. I can have one by Monday brand new from MBZ dealer for $84.00 my cost. I will rig up something after work tonight as a temporary fix.

Scott....You are right!!!! MBZ should have done this!!!!!!