Mirror switch backlight trivia and how to

[XR7-4.6]

In the long list of plausible “what-if”s with the MN12 platform - what if there was a SVT, what if there was a 1998 model etc - this piece of trivia might be well in the basement, but it is the most obtainable to you for literally $20!

I am of course talking about a LED backlit mirrror switch, something Ford fully engineered(in which I’ll go into detail below) but never actually implemented, on MN12s or other cars of the 90s-00s that used a similar switch. Here I will show you the evidence of the intended function as well as show you exactly how to finish the job yourself.






Here is a stone stock 94-97 mirror switch



Many many years ago I was sitting in traffic and fidgeting with things as one with ADHD does and wound up pulling the switch right off, and was relatively surprised to see I hadn’t broken it but revealed a translucent inner body to it, and then found the white outer switch arrows were translucent themselves



So what is one to do with such a revelation? Well take it apart of course! See what I see?



An 8 pin connector with just 7 pins

Must dig further!





Lots of dielectric snot! Eew!!!!

Let’s clean that up a bit shall we?



Now things get a little more interesting. You can spy a few unused holes in the circuit board… not only that, flip it around and reveal a plastic spacer piece with a curious rectangular hole…



Given the placement of such things you might deduce that these were intended to house a 3mm LED a load resistor and an extra pin powered by the ignition? Well let’s put that theory to test

 

[XR7-4.6]

Part two: Let’s finish Ford’s job




*warning* I am not responsible if you destroy your mirror switch, you need to know how to use a soldering iron. *warning*

Here’s what you’ll need:

- Soldering iron and solder(I use thin 60/40 Rosen core)

- Super bright 3mm LED in green( *note I’m not entirely satisfied with the color hue… I’d actually like to experiment with yellow with a green diffuser in the future to better match the switch lighting but for now we’ll keep it simple)

-470-1000ohm 1/4 watt resistor

- a used mirror switch and connector (don’t worry about condition, and there are other ford besides MN12s including SN95 Mustangs that have what you need)

First that tan spacer piece needs to be removed. You’ll find that there is a terminal that goes through it that prevents it, so you’ll need to desolder it from the other side. What I do is use a needle nose vice grip on the terminal that dangle and whilst holding the circuit board tap your soldering iron against the joint, gravity will simply let it drop.



Now that that’s out of the way you can simply spread the outer terminals out of the way to remove the spacer



With the spacer out of the way you now have full access to the bottom of the circuit board here you can now add your resistor



And on the other side your LED. Rule of thumb, the long leg is the + side. If you follow the path it will be terminal - resistor - LED - ground(shared with the main switch ground)



From here you may now solder the LED and resistor(be conservative on the shared terminal pad though)



Now you can put the tan spacer back in place and bend the terminals back over it to secure it



That arbitrary rectangular cutout makes sense now doesn’t it, eh?

So now you just need to put the center terminal back



And using a terminal from your used mirror switch add to to the pad next to the resistor



My trick with adding the “new” terminal is to place it where it goes and use the vice grips to hold it in place to the adjacent terminal.




From here you can put the switch together. Remember to reapply dielectric grease(don’t worry about liberal application, the light will shine through it) but make sure to keep the contact block exactly centered, there should be no resistance putting it together beyond the clips, if there is you might damage the switch.



Once together the switch is done. All you need from here is a terminal from the doner connector end, which you can unclip with a small flathead screwdriver. Doesn’t matter what wire color you choose, run it to the unused pin in your cars connector and splice it into the white/purple wire in the adjacent lock/window harness

 

[Grog6]

This is a wonderful addition.
This elimination is exactly due to a beancounter saving money for ford. it falls in the "nice, but not necessary" category. And they couldn't really do two parts, due to inventory costs.
When I bought them in 08 or so, 3mm green leds were ~$0.003 each, and a 1% metal film resistor was $.0012 each, So a few dollars per million units savings.