R107 Headlight Switch Problems

The headlight switch on an R107 is a rotary knob on the dashboard to the left of the steering column. It controls the parking lights, headlights and, on many cars, the fog lights when pulled. After decades of use, its contacts wear, and a whole set of lights can start to flicker or fail.

Symptoms of a bad headlight switch

• Headlights flicker or turn off when you touch the knob
• Parking lights or tail lights work only in one switch position
• Fog lights do not come on when the knob is pulled
• The switch feels loose or gets warm
• Dash lights work but headlights do not, or the reverse

Before blaming the switch, check the fuses and the bulbs. See electrical troubleshooting for the fuse checks.

How the switch works

The headlight switch feeds the parking light circuit and the headlight relay or main light circuit, depending on year. High and low beam selection is done on the combination stalk on the steering column. If the high beams or flash-to-pass do not work but the low beams do, the problem is probably the combination switch, not the headlight switch.

Removal

1. Disconnect the battery.
2. Remove the knob from the shaft. On many R107s, the knob comes off after releasing a small catch; procedures vary by year, so check the manual.
3. Unscrew the retaining ring on the front of the dash.
4. Reach behind the dash, usually after removing the lower dash cover on the driver’s side, and pull the switch out.
5. Label each wire or take a photo before disconnecting the connector.

Dash lights dimmer

The instrument light dimmer on the R107 is a rheostat that controls the brightness of the gauges and switch lights. If the dash lights do not work at all but the parking lights do, check the dimmer position first; it may be turned fully down. If turning it makes the lights flicker, the rheostat is worn. See instrument cluster and dash lights.

Replacement

Replacement switches are available from Mercedes and specialist suppliers. Some owners clean and adjust old switches, but a switch with burned contacts should be replaced. Use the correct switch for your year and market, since US and European cars differ, especially for fog lights.

Related bulbs

Check the bulbs when lights fail: the headlight bulbs or sealed beams on US cars, the fog light bulbs, the parking lights and the tail lights. A failed tail light bulb can also make the dash warning light come on on cars with a bulb check. If you want brighter lighting, see European headlights.

Quick answers

• Why do my headlights work only on high beam? Check the low beam fuse and the combination switch.
• Can a bad switch cause a fire? A badly burned switch can overheat. Replace it.
• Is the switch the same on all R107s? No, it varies by year and market.
• Why does my fog light not work? Check the fuse, the bulb, the relay and whether the switch was ordered with fog light function.