I'm happy to see this topic wake up, as I currently have a box of E-codes (Hella ECE, not VisionPlus) sitting next to me AND my bay has long been converted over to relays and 12-gauge. My understanding (??) is that since I have the pre-91 sealed beam, that its a straight swap other than connector style {ed: nope, same connector, sealed beam vs H4} and that later owners have additional work to do regarding retrofit of trim and a support bracket.



I have an HID 4300K retrofit on another car that has separate high beams, and it seems to work fine and I like them, but then I heard that the "secret" is that car has projector style reflector/glass geometry. While I was researching HID bi-xenon for use on the Aero with integrated hi/low, I found it stated clearly on forums that HID bulbs will cause a mess in the light pattern when paired with reflector/glass that is not designed for it and you will fail to gain an overall advantage over halogen. Therefore I'm using halogen and killed all thoughts of HID.

 

The aim of an HID bulb in an E-code H4 housing will not be as sharp as that of a H4 halogen bulb. But that's not a bad thing; it's what I'm using now in the 87 Mustang.

I think I mentioned this before, but one of the problems with HID in a well-designed reflector/projection housing is that they have this nice sharp cut-off at the horizon level, where a lot of the light is sent for better distance illumination. This is great if the road is smooth. But if the road is bumpy, the pattern jumps up and down with the vehicle, and that sharp cut-off can really dazzle on-coming drivers or the drivers in front of you in their rear-view mirrors. What they'll see is rapid changing of bright/dark patterns that can be very distracting.

In my 200mm E-code H4 housing, the focus is less precise, and the patterns have much softer cut-off. So the light/dark transitions of the pattern cast onto other drivers are a lot less abrupt, and therefore less distracting.

Now, when the aftermarket makers play games with mirrors to try to change the focus of the arc between the low and high beam patterns, they may or may not have the optics set up correctly to put the light where they need to be. So those lights may cause more problems with stray patterns than those that come from the factory with those designs. I modified the front light configuration to install a set of driving lights in place of the original turn signals for the high beams, so both the low and high beams are fixed. I moved the turn signals into the housings of the corner marker lamps, where they'll work better as turn signals.