Rebuilding an m-series 3-lever master light switch

  1. Introduction
  2. Removing the switch
  3. Opening the switch
  4. How it works
  5. Further opening the switch
  6. Repairing broken pins
  7. Cleaning the circuit breaker
  8. Re-assemble the inner half
  9. Clean the contacts
  10. Grease the internals
  11. Putting it back together
  12. Re-install and test
  13. Final thoughts

Introduction

 From 1957 until 2002, m-series vehicles used the same light switch, the venerable 3-lever switch. The top lever, unlocked by the right lever, switches between service and blackout modes, and turns on and off the headlights. The left lever controls the panel/gauge light brightness and the parking lights. As these switches get older, they tend to have problems - new replacements are only $50-$80, but if you have a day spare, you can clean and rebuild the switch you already have. Common problems include needing to wiggle the levers, one or more outputs not working, and the internal circuit breaker tripping randomly. If you did a 12V conversion, you can also upgrade the circuit breaker to a higher current, to power the new bulbs. Since I couldn't find much online about these switches, I decided to write this - enjoy!

Removing the switch

 First, reach up under the dash, and unscrew the big connector - make sure to unscrew the front half, not the back half. If it's stuck, you might need to get a wrench around it, but be careful not to damage it. Next, remove the levers, followed by the four screws in the corners. Now, if your screws are anything like my screws, they've spent the last 40+ years seizing into the switch housing, rusting to the dash, and are under about ten coats of paint. If you want to get them out without stripping them, go to harbor freight (or a reputable store if you so desire), and pick up an impact screwdriver - the type or whack the back of with a hammer. The HF one is $6.99, and they come in handy pretty often. It looks like this:

Put the right tip in, stick it in the screw, turn it counterclockwise by hand, then whack the back with a good-sized hammer repeatedly until the screws are loose. Once they're loose, you can remove them the rest of the way with a normal screwdriver. Reach under the dash, pull the switch through, and head for your shop / garage / kitchen counter.

Opening the switch

 Your switch should look like the one in the above picture - if it doesn't, it's a different version, and the information on this page may not all apply - so take yours apart and write your own writeup! These switches are held together by a snap ring in a groove in the outside housing. You can see it here, with a gap in the middle:

Use a pointy object to get under the ring and start prying it out, like such:

Work your way around the edge, using a flat screwdriver to keep prying it out. If yours has been apart recently, or otherwise isn't corroded into a solid blob, you may wish to put a C-clamp on it, as it's under a fair bit of spring pressure:

Keep prying until the ring pops out:

Now, if yours is like mine, the clamp wasn't too useful, as not only does it not spring, but you need to beat it against solid objects to work it loose, then pry up with a screwdriver:

Eventually you'll work it loose, and it'll begin to slide out. If you don't want to lose track of all the pieces, keep it upside down (that is, with the levers on the bottom) until it's apart, as that's the direction that makes everything stay in place. When you've gotten it up so you can see the seal, it's ready to come apart:

When you pull the two halves apart, the white sheet may come off on one side or the other:

Whichever it is, set it aside, you won't need it for a while. You can now see the insides of the switch - two sets of contact pads on the back half, and two rotating wiper assemblies on the front half:

Sometime around now, at least on mine, you get the whiff of severely burnt plastic.... Hopefully yours smells a little prettier!

How it works

 On the front half, two sets of wipers are connected to the two levers on the front, a larger one for the main mode switch, a smaller for the panel/park control:

The black plastic wiper assemblies lift out, letting you see the mechanicals underneeth:

When you rotate the lock lever, a catch is lowered out of the way of the disc on the main lever, letting it rotate to any of the settings:

The two flat springs between the discs provide the click action - there is a series of bumps stamped into the bottom disc, which depress the springs as they rotate, providing the positive stops on each setting. There should be a spring from the lock lever to the clip on the right side of the top of the image, however my spring looked like this:

Well, that explains why the lock lever never worked right! If you have the same problem, any bit of spring steel could be used to make a replacement. I decided just to leave it out, as accidentally turning on the lights isn't a significant problem for non-combat use, and at least with the loose pieces removed, it wouldn't randomly jam like it did before. The lock lever still works as intended, it just stays in the unlocked position rather than springing back on its own.

With the white piece back on, you can see how the wipers rotate:

Here's the main wiper assembley, in the off position:

I removed the springs from the contacts, to let is sit flush - normally the contacts are pressed down by three small springs. Here it is in both of the blackout positions, showing the triangular contacts connecting the inner rings to the outer bumps:

Further opening the switch

First, remove the O-ring from the housing, being careful not to tear it. A really thin screwdriver down the side can help. Start popping it out of its groove...

Then get a screwdriver under there and start gently prying all the way around:

The contacts should start to pull through the rubber part of the connector:

Yours will hopefully all pull through, rather than leaving two sticking up like mine did! Keep evenly prying, until it comes apart:

Here's more views, showing how it's put together:

The long loop around everything is the resistor for the panel dim setting - be careful with it, as it's hair thin wire. The black block on the lower right is the circuit breaker, with the contacts underneeth it.

Repairing broken pins

 Hopefully you can skip this step - and if you do find a switch like mine, go buy a new one! However, I wanted to get this one working, so I went ahead and fixed the broken pins. When I pulled the inside out, the plug looked like...

And the inside...

D'oh! Well, at least that explains why going over bumps and wiggling things always made all the lights flicker! The ends of the pins are both corroded from years of being broken, and burnt from frequent arcing. I had two contacts completely broken off, and one almost broken all the way through - you can see it crooked in a lot of the images. Here's the main power feed:

"Well there's yer problem!" And here's the mostly broken one:

And the two pins.. note the pitting from arcing every time my lights blinked:

First step, clean them up nice and shiny:

And then solder them back onto the stubs:

Again, if your switch also has broken pins, getting a new one is probably a better bet - getting solder to wet these was a pain, and the life expectancy of the fix is unknown.

Cleaning the circuit breaker

 Many people have problems with the circuit breaker - the contacts get dirty or worn, causing the bimetal strip to heat up quicker, and trips at incresingly lower currents every time. Easy enough to fix - use a small screwdriver, and stick some sandpaper in:

Slide it back and forth, wiggle it around, etc. Then flip the sandpaper over and repeat to get the other contact. When that's done, use a piece of cardboard to do the same:

This will get out any little particles that could keep the contacts from closing properly.

If you're running a 12V system, you could either drill out the rivets and use a larger circuit breaker in its place (miniature ones, smaller than the one used in the switch stock, are available in 20A and 30A at most auto part stores, which should be plenty for most 12V conversions), wire up a second circuit breaker in parallel (they'll share the load, or at least mostly share it), or jumper the circuit breaker with a piece of wire and use an inline fuse or circuit breaker in the wiring harness before it feeds the switch.

Re-assemble the inner half

Once you've cleaned or replaced the circuit breaker, it's time to put the inside back together. Start by healthly greasing the rubber plug with any dielectric grease:

The grease will both aid insertion and make sure it's waterproof. Carefully insert the inside, making sure to line the pins up with the holes, and gently press it through.

Clean the contacts

 Your contacts are probably dirty, burnt, or otherwise a problem. Take the inside...

And flip it upside down and run it on a piece of sandpaper:

Then get any places that didn't get by hand, and you'll have shiny contacts: (I also soldered a rivet with a corroded-away head to the contact it feeds)

The wiper contacts look like:

Each one has a small spring to press it against the contacts. Remove them, replace any broken springs, and rub the sandpaper on them by hand. Don't use a flat surface like for the other contacts - you want these to be rounded, not flat - just use your finger to press the sandpaper into them. Put the contacts back on the plastic arms with a spring under each one, and make sure they move freely. If they bind, try rotating it 180 degrees, or swapping them around with others of the same type,

Grease the internals

 Go back to the other half of the switch, and clean out as much crud as you can, being sure to get the mating surface of the two halves clean:

Remove the two switch shafts, and clean them too. Then, using any good grease, get all the moving parts:

Put some dielectric grease around the contact pads on the back half, then put the white plastic sheet on top, then liberally grease the paths the wipers rotate in. The grease on the back will hold the plastic in place during re-assembley, and make life a lot easier!

Putting it back together

 First, put your wiper arms back on the lever shafts:

Pop the big O-ring back in its groove, and apply more grease:

You should now have two halves - do a check of the workbench for any parts that escaped....

Flip the back over, and start inserting it into the top. Be sure not to bump the bottom half or turn it sideways or upside down, or all the little contacts will fall off, and you'll have to take it back apart to put them back in place.

Start pushing the halves together. The O-ring will probably catch, so you'll need to go around the edge and pop it down into the housing. Since you're fighting a lot of spring pressure, it's time for the C-clamp again. I got out a nice big one, and used a small screwdriver's handle as a spacer so I didn't press against the lever shafts:

Gently tighten the clamp, being sure the O-ring doesn't get pinched, until the two halves are back together. At this point it can be turned sideways again or moved around, as the contacts are now firmly in place. Start the snap ring on one side:

And work around pushing it in. If it pops up like this when you remove the clamp....

You probably didn't have the clamp tight enough, or you deformed the snap ring prying it out, in which case you need to carefully bend it back into shape. It took me a lot of wrangling to get it back together, so take your time, and be prepared to pop the snap ring in and out a bunch of times...

Yay! If all went well, you have one of these again:

Re-install and test

Take it back out to the jeep, push it through the hole in the dash, re-install the four screws, re-install the levers, screw the plug back on, and it's time to test it out!

Flip it through all the settings, making sure every light works, and go for a drive to make sure your switch is nice and reliable - after all, not buying a new switch gets you almost a tank of gas! (If you have a jeep, not anything larger, obviously...)

Final thoughts

I hope this writeup helps someone - enjoy!

And yay! I have lights again!