I had asked Bstollmaier about opening his headlights and this is what he had answered me:
These are the first ones I've done so I have nothing to compare them to. I used a heat gun and yes, I had to fight them a bit. I'd say the most important thing is to make sure you heat the adhesive well, what I mean is keep moving the gun over a large span to heat up a lot of adhesive and be patient. Don't hold the gun in one spot and melt the plastic and don't keep prying if it won't budge. Instead heat more until it is pliable. You will bend some of the plastic as you pry and that's OK, it doesn't affect the light. The plastic rim will be deformed when it's all done but in my view it doesn't matter as you never see it unless the hood is up. Once you start getting part of it apart it gets easier because you can start prying and heating at the same time. I placed the heat gun on a bench and used both hands to pry. That way it would separate as it heated. Patience is key.
Hope this helps... What is your plan? Are you going with one of those switchback LED strips?
I agree 100% with what Bstollmaier said. I used a $60 Kobalt model HG2000 heat gun I picked up from Lowes. It has multiple temp settings, and I found slightly over 600 degrees to be optimal. It heats the plastic to a pliable "sweaty" point within 45 seconds--enough time to chip away and peel the adhesive. The process is indeed very long and tedious, but worth the wait for me. It took me nearly six hours PER headlight.
Why so long? First I heated parts to remove the adhesive that was exposed (the loose ends or excess parts of the adhesive). Then I reheated parts to start picking and prying away at the adhesive connecting the lens to the housing. Soon enough you will pry and remove enough adhesive to "squeeze" into the housing with a hooked tool and pry the lens from the housing. The lens is plastic and does bend during the pry and pulling process--but it does not lose its shape.
Yes, the outer plastic rim (of the housing, not the lens!) will be deformed, but if you are crafty enough, you can use the heat gun to heat the plastic and mold things back into alignment. It won't be clean and perfect as before, but not as warped as it used to be.
The Oven:
Pros: Lower temperatures; ideally faster; uniformed heating; ability to use OCI butyl rubber sealant offered by TRS.
Cons: Constant rebaking is likely; not as fast as many claim; uniformed but uncontrolled heating (you want to heat a certain part, but are forced to heat the entire headlight); high chances of warping the entire housing/lens if not careful; high chances of melting or warping the mounting points of the light (you won't find this out until it's time for reinstall).
The Heat Gun:
Pros: High temperatures; concentrated heating; can use any high grade rubber sealant.
Cons: Much slower; concentrated heating but high chances of warping specific parts of the housing/lens if not aiming the gun properly or concentrating the heat in one spot for too long; cannot use OCI butyl rubber sealant offered by TRS because it requires uniform heating.
Note: The key to the heat gun is to observe what I call the "sweat" point. If you aim the gun at the black plastic part, observe and watch the part start to sweat or glisten. This is the sign that the plastic is flexible, but delicate. This is the perfect time to pick/remove the adhesive and pry/bend/separate the lens and housing. Do not keep heating past this sweat point.
In my opinion, the gun is the better option. I've gunned two sets of headlights so far.
For one set, I kept the headlights standard, kept the chrome housing trim chrome, and simply removed the amber lens reflector. Clear everything. I also added 3M reflective tape to the "flap" adjacent to the headlight. This way, I have a reflector for nighttime visibility/safety/legal purposes. The tape appears black during the day, but shines white/silver at night from external light.
For the second set, I painted everything black and removed the amber lens reflector--similar to Bstollmaier's smoked out headlights. The only difference, is I added the 3M reflective to this set too.
I found it very hard to deform the lens at all. You would have to be seriously distracted or numbskulled to do that. It's not as intimidating as it seems.
