I agree with the above, possibly the bulb sockets if you have US headlights. The pins on 9004? (Can't remember at this point) bulbs are tiny and can't handle the current needed without getting incredibly hot so the sockets tend to melt. You can get replacements at autoparts stores but if I were you, I'd seriously consider spending the money to get some Euro headlights, the output is considerably better.

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Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.