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[kev]

EDIT:  February 2021
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There are many threads, topics, and even products out there on restoring the plastic finish on automotive lights, but I figured I'd share my experience on making on old beat up tail light look as good as a NIB Mitsu light assembly.  



The example...and goal:







That is a brand new-in-the-box starion passenger tail light assembly.   Lets face it....we won't be seeing photos of things like this much longer.   The NIB Mitsu products for our cars are very scarce these days.   It took Mr. Sexton at Southwest Mitsubishi a bit of time to locate this sucker for me...unfortunately there was no hope for finding its matching pair...


...hence the challenge:   Pulling out my old set of beat up starion lights and try to make the drivers side one look as good as the NIB passenger side:

[kev]

Starting point:

The light assembly must be free of cracks (specifically look for stress cracks in the outer plastic).  Don't worry too much about minor chips.  Also look inside the light...if you see signs of rust on the chrome plated deflectors in the bottom of the light, then you may want to find a better assembly to use as a starting point.  Even if you don't notice any cracks, if you have rust, you probably have a crack somewhere that is allowing the moisture to build up within the light and essentially causing the rust.  

Note:  I have had some experience with separating the light assembly to remove/replace the chrome deflectors in the past...but it wasn't an easy job.   Careful use of a heat gun and a lot of patience is the key...but that isn't in the scope of this thread.   This thread starts with a non-cracked and properly working tail light assembly.  


First step:  Clean Clean Clean.  

Start with soap and water.   I took about 20 minutes in my deep sink to clean of the light assembly using just Dawn dishwater detergent and warm water.  

Afterwards, let the assembly dry or use a hair dryer to speed up the process.   I used the hair dryer and let it blow into the light thru one of the bulb holes for about 15 minutes to allow the insides to dry up  pretty good.   Make sure the hair dryer isn't blowing too hot...you don't want to melt anything, you just want air-flow to cause the evaporation.

Then I cleaned off the entire outside of the assembly with solvent made for plastic....but you could use other solvents including waterborne wax and grease remover.  

It is so important that you start with a very clean surface, because our next step is wet-sanding.  The last thing you want to do is sand a bunch of dirt into the plastic lens.  

Here was my set of lights after the cleaning process.  Note the many many scratches and if you look close enough you can see a few chips in the plastic




Step 2:  Sand!

This is the major step of the process.   I started with 1000 grit, and wet sanded the assembly smooth.   This is the most important sanding step...the one that you eliminate all of the deep scratches and knicks in the plastic.  

Take your time and smooth out the knicks/chips.   Note that this is a scary step because it appears that you are ruining the light...but don't worry yet, we will restore the finish.   Just focus on getting out all of the imperfections.  

Also note, go ahead and sand the black plastic trim around the clear lens while you are at it.   And don't worry too much about the black painted 'stripes' on the lens itself...don't focus on them but don't worry if you start rubbing the paint off....its going to happen anyways.

Here is the result of about 30 mins of wet sanding with 1000 grit:



Looks cloudy but the chips and deep scratches are gone.  

Clean off the light with water and wipe it dry with a micro-fiber cloth.


Next step:  more and more wet-sanding.   Our goal now is to restore the finish of the light by simply stepping up in grades of sandpaper...hence making the scratches caused by the sanding process less and less deep.  

So go to 1500 grit....



Keep the light nice and wet during sanding.  I didn't use a block, just hand with very mild pressure.  Remember you aren't sanding out imperfections anymore, you are just smoothing out the finish.  Remember to get the black plastic trim as well.

Don't forget to clean off the light and wipe down with a micro-fiber towel after each sanding step.  You do NOT want remaining residue from the former grit sanding step in with the mix, it basically negates what you are trying to accomplish

Note:  Micro-fiber towels are awesome to wipe things down without scratching, but first carefully remove the tag on your towel.  It is amazing how that stupid little tag on the towel will scratch your part.  I ran into this a lot when cutting/buffing the finish on one of my cars after painting.

Anyways, after you are done with 1500 grit...go to 2000 grit...and then to 2500 grit.   I put about 10 minutes per step.  

Here it is at 2500 grit...looking better:

[kev]

Last sanding step...3000 grit. Some people never go this fine in grit but I swear by it!   I rather take the time in sanding the unit to an almost shine rather than buffing it.   Get it as smooth as possible with the sand paper and the buffing process will only take seconds.  

After this final grit, clean up your part really good with soap and water.

Here it is after 3000 grit....you can see the shine from sanding alone!  No polishing products, no buffing.....this result is from sanding!







Finally it is time to buff.   You could use a ton of products for buffing...I simply bought a small bottle of turtle wax headlight buffing compound:




Now,  using a polisher with a WOOL pad.   I buffed the light with the above compound.  

You could use a drill for this step if  you don't have a polisher or buffer...but it is good to know what rpm you are spinning the pad at.   For plastics, I use 1500 rpm!   Faster will heat up the plastic and melt it....slower will do nothing!   There is a fine line between  not polishing anything and overheating during the polishing process. Polishing is just that...heating up the part and basically molding out the scratches. This is the reason why I spend more time sanding than polishing.  It is easier to screw up polishing than sanding in my opinion.

Anyways....polish with the wool pad.  Only took about a minute.  Goal...rid the part of the sanding scratches.....the wool pad will cause it's own scratches as well but you can see which are from the wool vs the sanding based on the orientation of the scratch.  The wet-sanding scratches are straight, the wool scratches are spiral.



Clean and wipe off again with the micro-fiber rag:



Next, switch to a foam pad...same compound:




Don't forget to polish the black plastic trim while you are doing the clear lens.


Result of the polishing process...WOW!!

[kev]

Not done yet...now to address those black painted lines in the lens.  

Hard to see in the photos but with a combination of years of abuse as well as a result of the sanding process, the black painted lines on the lens are wore off in certain spots. So time to restore them.

Take 600 grit sand-paper and very carefully scuff up just the black painted portion.  Don't scratch the polished section!   Take your time...don't apply pressure just scuff up the surface:




Now tape over the black paint lines with GREEN 3M tape...don't use the blue or yellow...use the GREEN!!

Press the tape into the grooves firmly.  Make sure there are no bubbles, etc.   Then with a brand new blade in a hobbiest exacto knife, cut the tape out of the grooved areas where the black paint goes:



Finish masking the part in preparation for painting.

Now, use this paint:  SEM Trim Black, P/N 39143.   This paint is awesome!   It first lays out with peel but then levels after a few minutes.




Paint the part.




Let dry about 3-4 hours and carefully remove the tape:

[kev]

Lets compare parts:  the NIB mitsu passenger light vs. the restored old beat up drivers light





Looks great!  Only one minor difference...the newly painted black lines on our lens are a tad more dull than the NIB ones.   Remember that it has only been 3-4 hours since painting.....so take a micro-fiber cloth and lightly rub the paint.  This actually shines it up a bit.  Made it almost a perfect match.





Last is the two piece of trim.   Quick cleaning first with soap and water and then with Wesley's bleach white.




The one piece just pops on.  The other is glued on:

[KO]

Killer job Kevin, definitely will be doing this!

[kev]

Please see the top of the initial post of this thread, the photo links have been fixed.