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Headlight Switch Internals/Repair
 
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Pelican Technical Article:

Headlight Switch Internals/Repair

Paul Anders

Time:

2-3 hours

Tab:

$30-$400

Talent:

***

Tools:

Small flathead screwdrivers, Dremel tool with cut-off wheel, tweezers, contact cleaner, DVOM, Dielectric grease, tie wrap

Applicable Models:

Porsche 914 (1970-76)

Parts Required:

Components from a used but functioning switch or a new headlight switch

Performance Gain:

A headlight switch that functions properly

Complementary Modification:

Troubleshoot and repair the headlamp motor
     The headlight switch for the 914 is an insanely expensive item - something near $400 new! Luckily, there seems to be a fairly good supply of used switches on Ebay. I recently bought a switch, not because I needed the switch, but because the insert was wrong - it was the rare, early green fog light insert. I'd wanted this insert, but didn't want to spent $30 at AA for one! I won the auction and got the switch for $9, including shipping.

     After extracting the insert, I checked out the switch - the instrument rheostat wire was bent on the end and popped out. I decided to take the opportunity to see how the switch was made and if it could be repaired. Based on what I learned, here is a disassembly procedure with some photos of the internals. Hope this helps out anyone who might need to rebuild a switch. Note that there are two 914 switches - the "early" skinny one (the one you see here) and the "fat" late one. I don't know how much the fat switch differs...

  1. Remove the knob by unscrewing it from the shaft.
     
  2. The contact plate is crimped onto the body of the switch at the corners. If you have a lot of patience, time, and plenty of small screwdrivers to break, you can try prying the corners away. Or, you can take the easy approach and use a Dremel cut-off wheel and simply cut the corners away. Don't worry about how you'll get the top to stay back on - I have an ugly but very effective way of doing that in the last step.
     
  3. After the contact plate is freed at each corner, it will probably pop up near the front of the switch. To remove the contact plate without damaging the switch internals, you will need to hold the rheostat assembly (at the back of the switch) in place. Hold the switch by putting your fingers of one hand under the body and your thumb on terminals 58a and 58b. While holding these terminals down, slide the contact plate up over 58a and 58b, remove your thumb and slip the plate off. The rheostat will stay in the back of the switch. After removing the contact plate, the switch should look as below (the contact plate is flipped over to reveal the contact pads):

  1. It's pretty easy to see how the switch works. The contact slider block is keyed to the shaft. Each contact slider (there are three) is backed with small springs to press the slider into the contact plate. The bottom of the contact slider block has two springs that push plastic pins into detents in the body to "click" the switch into the three positions. All of the contact plates seem to be silver plated. The entire assembly is coated in dielectric grease for lubrication and to prevent arcing. The rheostat is keyed to the shaft and rotates a contact plate wiper against the resistance spring. Note that the rheostat assembly is electrically separate from the switch part.
     
  2. OK, let's finish disassembly. Carefully lift off the contact slider block from the shaft. There are two small springs in the bottom of the switch that push the plastic pins down - they may fall off into the switch body. Leave them there until later. Put the slider block aside. Pull the shaft out of the rheostat, and put it aside.
     
  3. If your rheostat is OK, leave it alone! If you need to remove it, be aware that there are two small springs that will pop it apart if you simply pull it out without holding it together. The retaining plate is simply held by shoulders and slots in the switch body. Put your thumb on it and pull upwards on the terminals - try to hold it together. Once removed, let the springs move the plate off of the slider and put the parts aside.
     
  4. Below is a picture of the disassembled switch:

  1. Repair will depend on the problem with your switch. Damaged rheostat springs can be repaired with careful use of tweezers. Damage to the sliders can be repaired with good parts from another switch. Damaged contact plates will need to be replaced with a good part from another switch. Worn out contact slider block pins can be replaced with good parts from another switch.
     
  2. Reassembly is fairly straightforward. Use contact cleaner and clean the old grease off of all parts. Coat the bottom of the switch bottom, spring guides and springs, contact plates, pins, and contact plate with dielectric grease. Reassemble the rheostat by stacking the retaining plate, rheostat slider plate, springs, contact slider, and rheostat plate together and insert the assembly into the switch body (make sure the retaining plate is oriented so that the tabs at the top limits the rotation of the rheostat slider plate). Slide the shaft into the switch body and key it into the rheostat. Reassemble the contact slider plate - use a good amount of grease on the springs and pins to hold them in place so that you can slip the slider plate onto the key in the shaft without the pins falling out into the switch body. Make sure you orient the contact slider plate as shown in the top photo. Slide the contact plate back on the top and over the rheostat contacts.
     
  3. . If you carefully bent the corners out when you disassembled the switch, you may be able to bend them back to hold the contact plate in place - good luck. If you used a cut-off wheel as I suggested, you could use epoxy to reaffix the contact plate, but you're in trouble  if you should need to disassemble the switch. Instead, use an ugly, but effective and removable way of holding the plate on - a tie wrap! See the photo below for where to run it through:


 

  1. . You're all done. Use continuity tester or DMM to check the switch operation before installing. Diagrams of the switch internals are at the Pelican Parts web site in the 914 electrical diagrams area.


UPDATE: Regarding the newer "fat" version of the switch
Contributed by:
Tim Kutscha
tim_kutscha@yahoo.com
 

I've included this image to show the later "fat" headlamp switch for comparison.

I've wiped off the dielectric grease so you can see the contacts better.

The only major difference between the "skinny" switch and the "fat" switch is the contact plate on the left. The "skinny" switch passes all current for the headlamps and the headlamp lifter relays passed through one contact(#56). I suspect that all this current causes switch failures, so in the "fat" switch, current for the headlamps goes through one contact (#56) and current for the headlamp lifters goes through another contact (#56K).

Note that in the "fat" version, the contact slider on the left is the same as the two contact sliders on the right. In this picture the contact point driving the headlights is completely burned off and the contact plate it touches was rather corroded. I was lucky enough to have a second "skinny" switch to cannibalize for a good contact slider. If your headlamp contact point is burned off and you don't have another switch to take a contact slider from, you can swap the contact slider on the left (headlamps) with the contact slider on the bottom right. The only functionality you will lose is the parking light indicator on your dash (note parking light contact in picture).

A few other minor points:

- Since I'm cheap and don't have a Dremel Roto-tool, I used a metal file to file down the corners to open up the switch instead of prying them with a screwdriver and it worked fine.

- I got confused by the Haynes manual directions for removing the lamp switch. It says to follow the directions for the hazard light switch. Those directions say unscrew the knob AND the shaft.  For the headlamp switch, you can NOT unscrew the shaft (note the scratch marks on the shaft in the image). Just a heads up.
 

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