What you have in ECE headlamp is the city lamp which is a small bulb
beneath the headlamp bulb. You can switch the wire from US DOT side
running lamp to the ECE city lamp. The pigtail is for negative earth, I
On the W126, both ECE headlamp with H4 bulb and US DOT sealed beam unit
have same 3-pin connectors. I've installed the ECE headlamps on my US
model with no problem.
PS The euro-style headlamps with "Circle E" and requistive regulatory
glyph symbols on lense are ECE headlamps. The crappy ones on US Mercedes
in the early 1980s are SAE DOT.
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