Hello,
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 believe.
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.
Regards, Oliver
PS The euro-style headlamps with "Circle E" and requistive regulatory glyph symbols > I recently purchased a pair of single-lens euro style headlights for a
1985 500sel (US MODEL). The headlights I purchased have a single 5-pin
> connector on the back of each headlight. However, the headlights now
> on the car have a 4-pin connector and a pigtail running off the wiring
> harness with a 3-pin connector on it. I Would appreciate advice on how
> to properly install the headlights. Thanx.