Another conundrum -- Rear License Plate Light housing

[Namerow]

I'm in the midst of 'restoring' the license (licence?) plate light assembly for my 70 Z.  For those familiar with these units, you'll know that many are heat-damaged so that both the outer shell (black plastic) and the inner base plate (white plastic) sag and no longer seal well, esp. along the top seam and despite the rubber gasket.  The illumination is, of course, provided by two #89 bulbs.  These apparently generate enough heat during long periods of lights-on driving to cause the plastic pieces to soften and deform.  The housing assembly is 98% sealed (there are four small, open drain holes on the bottom surface of the outer shell) to keep out water, with the reverse effect that it seals in the heat.  I have a couple of questions for anyone who's tried to remedy the situation:

1. Clipped inside the black outer shell are two zinc-plated, stamped-metal insert plates.  They fit over the clear-plastic 'lens' surfaces on the left and right side of the shell, such that they block the center 70% of the lens, leaving only the sides of each lens (and a little centre slit) open to light passage.  Some say that these metal inserts are to keep heat away from the clear-plastic lens, but I find this hard to believe.  Metal is a pretty good heat conductor and these things sit right on top of the clear-plastic lens surface, so how they act as heat protection is beyond me.  My guess is that they're actually installed as 'shades' because -- for some markets - Nissan decide that the fully-open clear-plastic lenses allowed too much illumination onto the license plate.  I'm wondering if they're possibly responsible for the excessive heat build-up inside the housing.
   
   Anybody know the real reason for these metal inserts being installed?  Were they also found in Euro-market or Japan-market Z's?
    
2. Given the heat build-up issue, the license plate light assy seems like a perfect place for substituting LED's for the OE incandescent bulbs.  Has anyone tried this?  Is it a plug-and-play solution, or do the bulb sockets and connections need to be modified?  Where were the LED's sourced from?
    
3. There's been debate in the past over the correct colour for the 'black' outer shell.  Some say that this piece was painted by the factory so that it has the same 'anthracite' grey colour as the taillight finisher panels.  I believe that a photo of a MIB unit was produced to support this idea.  Paint overspray on the white base piece was pointed to as proof of the spray-painted final finish treatment.   I've checked some pictures of a bone-stock '70 that was recently listed for sale and it, too, shows the license plate light's housing to be the same colour as the taillight finisher panels.
   
   There's just one problem.  I have three of these light assemblies (one from a  '70, two from '72's) and in all cases the outer shell is unpainted and matte black in colour/texture.  There's not a trace of paint on the outer shells.  They haven't been sanded, because the matte surface texture is molded in.  There is paint on the white base plates, but it's flat black, not grey, and it doesn't seem to have been applied with any purpose in mind -- partial surface coverage, and not very good at that (which makes me wonder why the supplier that produced these pieces for Nissan had somebody randomly waving a spray gun at them loaded with flat black paint).
   
   So:  Were the outer shells painted.  Or not?
    

Thanks to anyone who can shed some light on these questions!

Edited April 20, 2016 by Namerow
added items

[siteunseen]

I painted mine back to the graphite color when I bought it.  It was painted black as was the finisher.  I've always thought the dealership did it when they put the black rocker stripes and the black spoilers on.  The reason for thinking that is behind the tag is the only part of the car that's painted black, like they didn't pull the finisher off.  Just taped off the lights and stainless strip and sprayed it with no tag.  My other 240 is the body color behind the tag, not black.

I think that metal is to keep the bulbs from melting the clear lenses, my guess. 

Here's a picture from the day I got it home.  You can see the black where the tag holder is.

Here's the other one;

 

[cbuczesk]

The plastic light housing is molded in black and doesn't get painted. The metal panels should be a slightly darker gray than appears in the picture. In the Mopar world we use dark argent paint for that color. LEDs should be good back there. The metal slip things could be for heat or maybe to create a more even light instead of a spotlight effect.

Chuck

 

[siteunseen]

Yes the finisher on the red car is more silver than the oe color. The guy I bought it from did that color. It looks okay on the red and white so I've left it alone.

I did not know the light housing was unpainted. Thanks Chuck for that info.

[CanTechZ]

11 hours ago, Namerow said:

 

1. Clipped inside the black outer shell are two zinc-plated, stamped-metal insert plates.  They fit over the clear-plastic 'lens' surfaces on the left and right side of the shell, such that they block the center 70% of the lens, leaving only the sides of each lens (and a little centre slit) open to light passage.  Some say that these metal inserts are to keep heat away from the clear-plastic lens, but I find this hard to believe.  Metal is a pretty good heat conductor and these things sit right on top of the clear-plastic lens surface, so how they act as heat protection is beyond me.  My guess is that they're actually installed as 'shades' because -- for some markets - Nissan decide that the fully-open clear-plastic lenses allowed too much illumination onto the license plate.  I'm wondering if they're possibly responsible for the excessive heat build-up inside the housing.
   
   Anybody know the real reason for these metal inserts being installed?  Were they also found in Euro-market or Japan-market Z's

Thanks to anyone who can shed some light on these questions!

I decided to take my rear license plate for cleaning after reading your topic (and because I have been planning to) and I found something interesting.  My license plate light has only one "metal shade", on the left side, and that side is noticeably more deformed from heat build-up than the right side. I think your theory about heat build-up is correct. Here are a few pictures of mine:

[Namerow]

Great photos, CanTechZ.  Couldn't have asked for a better real-world illustration of the (good) possibility that those metal inserts have nothing to do with heat protection and, in fact, create the opposite effect. 

Auto manufacturers never spend money on parts that don't have a purpose.  These insert plates look like they were designed to be installed only in particular situations.  Otherwise, the housing looks perfectly happy (very happy, in fact) to have them left off.  My theory is that the plates are shades and were only installed for markets where there was some government-enforced limit on the amount of illumination that could be used on the rear of a vehicle above and beyond the left and right 'running lights' (brake and turn signal lights don't count, because they're occasional and short-duration).   It will be interesting to see if anyone from Europe (or Japan) reports that their lamp housing does not have these insert plates. 

At this point, I have one good housing assembly and I don't want to have it warp.  I'm thinking about ditching the insert plates and maybe reducing the wattage of the bulbs, too (add something to the circuit to create a voltage drop?). 

Conversion to LED's would be another way to get rid of the excess-heat issue, but it looks like it could turn into a 'project' (unless, of course, there's an available LED with the right combination of beam pattern, lumens, and bayonet fitting size).

[Namerow]

Answering my own question, I've found that there is an LED bulb that's a direct replacement for the #89 incandescent versions.  'Tower' type, with 210-degree illumination spread, medium-low lumens output.  Correct socket size & pins, matching 'bulb' diameter.  That's probably the way to go.

Regarding colour treatment for the black-plastic housing cover (i.e. should it be left as plain black plastic or painted to match the rear finisher panels?), I'm still perplexed by photo of this apparently-unmolested '70...

Looks grey to me.

[Patcon]

Do you have a link to the bulb?

[Namerow]

2 hours ago, Patcon said:

Do you have a link to the bulb?

https://www.superbrightleds.com/moreinfo/tail-brake-turn/67-led-bulb-15-led-forward-firing-cluster-ba15s-retrofit-car/169/#/tab/Overview

Note that this vendor's site provides a search-by-vehicle / search-by-application function that returns a faulty result for the license light application (it recommends an 1156 bulb/socket --  that won't match an 89 socket/or bulb).

[Patcon]

Thanks. I have dealt with them for under cabinet LED's pretty good to deal with

[Namerow]

More on the topic of black vs. grey...

Here's a different Z that was recently up for sale.  In this case, the license plate light housing appears in basic-black, unpainted condition.  To my eye, it just doesn't look right.

 

[Mark Maras]

5 hours ago, Namerow said:

More on the topic of black vs. grey...

Here's a different Z that was recently up for sale.  In this case, the license plate light housing appears in basic-black, unpainted condition.  To my eye, it just doesn't look right.

 

 IMO, License plate light cover should always match the color of the rear panel regardless of the color. This combination looks like a black fender on a silver car.