[DML] DIY Door Light Switch Upgrade: Magnetic Switches

[Joe Angell <jangell@xxxxxxxxxxxxxxxxx>]

Not too long ago I found that my door lights were staying on when the  
doors were closed.  Repeated closing of the doors finally took their  
toll: the switches still worked, but the plastic that they were  
mounted in had collapsed and bent, so the switch no longer pointed at  
the door and thus didn't completely depress.  I tried using shims,  
but that didn't help with switch's aim.

I figured that even with the shims, this would eventually happen  
again, so I decided to go with a cheap, contactless solution that  
required no permanent modifications to the car and no new wiring:   
magnetic switches.


Parts:
- Three cylindrical magnetic switches (replaces existing switches):   
$2 to $5 each
- Three rubber grommets (to mount the switches in the old holes):  
$0.50 each
- Six blade-style connectors and crimp tool (to connect the switches  
to the existing wiring):  You likely a
- Three rare earth/neodymium magnets (mounted on the doors to trip  
the switches):  $20 for a bunch
- Black Paint (if your switches/magnets aren't black): $3.00 for a can


   Magnetic Switches:
I went online and found a pair of magnetic switches, which are  
commonly used in security applications.  They're pretty simple:  the  
switch changes from on to off depending on how near it is to a  
magnet.  The ones I got are small cylinders, about 1/4" or 3/8" or so  
in diameter and an inch or so long.  I went with cylinders (also  
called "recessed") because they would fit through the hole where the  
old switches were mounted.  I don't have a link to the ones I  
actually got, but here are some quick Google matches; they all  
basically work the same way:

	http://www.google.com/products?q=recessed+magnetic 
+switch&hl=en&um=1&sa=X&oi=froogle&ct=title

Magnetic switches are listed has having a 3/8" or 1" or what not  
"gap", which is how close the magnet needs to be to the switch before  
it changes states.  I think this mostly refers to the strength of the  
magnet it comes with; if you want to try to use the magnets it ships  
with, you'll want to get switches with the largest gap you can find.

The only other issue is to make sure you get a switch that is  
normally in a state that will ensure the lights are off when the door  
is closed.  I managed to get the wrong ones, so I had to use a  
transistor to invert the state.  I remember thinking that I needed  
normally closed switches (ie: completes the circuit when the magnet  
is not near the switch), but they operated like normally open  
switches when I they arrived.  If in doubt, you could probably just  
get one of each kind -- they're only a few dollars a piece, and it'll  
certainly be easier (and use less wires) than the transistor method I  
wound up using.


   Switch Mounting:
You want a switch that is smaller than the hole that the old switch's  
wires go through, since that's where you'll want to install it.  To  
mount mine, I took the switch to the hardware store and found a  
rubber grommet that it fit snugly into.  The grommet itself mounted  
securely into the old switch hole with no tools or glue.  I also  
painted my originally light grey switches black so they wouldn't  
stand out.  The final installation is nearly flush with the trim and  
looks surprisingly professional.

After mounting, you just crimp on a couple of blade-style connectors  
and plug the two wires from the old switch into the new switch, and  
the lights on the doors should go on.


   Magnets:
To get the lights to turn off, you need to mount a magnet on the  
door.  The switches usually come with magnets, but I found them too  
weak for what I needed; that part of the door is surprisingly far  
away from the switch when closed.  I wound up going to ThinkGeek.com  
and ordered a $20 collection of rare earth (neodymium) magnets.  This  
gives you a bunch of magnets to try, and spares in case you lose one,  
and they have a much greater range than normal magnets:

	http://www.thinkgeek.com/geektoys/science/770f/


   Magnet Mounting:
I didn't need to glue the magnet to the door or drill any holes, as  
there was already a convenient metal plate there that old switches  
pushed against, and I could just stick the magnet to that.  The  
magnetic switches I got were somewhat finicky about where the magnet  
was:  as long as it was inline with the switch it worked, but if it  
was off to the side too much it wouldn't.

To figure out the proper placement of the magnets, I removed the door  
switch, closed the door from the inside, and marked the door plate  
through the switch hole with a chalk pencil.  I then just placed the  
second longest cylindrical magnet from the set to the marked location  
on the door plate; the magnet is strong enough that the door lights  
go off when the door closed to the point that you can feel the  
striker pin pressing against the latches, but the latches aren't yet  
engaged, which is pretty much what I wanted.

The magnets haven't fallen off the door yet, but it might not be a  
bad idea to use a dab of super glue just in case.  I've also been  
meaning to paint the magnets black, since the small chrome cylinders  
on the door stand out a little.



The total cost of this project was about $40, which includes the  
switches, grommets, paint, shipping, a bunch of extra magnets, and  
the transistors.  The magnets were easily the most expensive part,  
but that's because I got far more than I needed.  You might be able  
to find switches that ship with stronger magnets and not need to get  
the extra set from ThinkGeek or elsewhere, or just buy smaller  
quantities of stronger magnets, or you could mount your switch so  
that it sticks out more and thus is closer to a weaker magnet when  
the door is closed.  You probably already have paint, blade  
connectors and a crimp tool, so no need to add those to the price.

Overall, the magnets seem to work quite well, and I haven't had any  
problems with my door lights since I installed them.

I can post some pictures if anyone would like to see final the  
installation.  I can probably put together some kits and make them  
available for sale if there's enough interest, although as you can  
see there isn't really a whole lot to this.  A kit would probably be  
about in the $20 range.

-- Joe




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