The 300F wiper switch (and probably G, H maybe others) has a few problems
that can drive you crazy, mostly around the washer button.
First some background; wiper blade action troubles are seldom the switch.
It is a very rugged thing, well built and reliable. There are two things that can happen, however.
Number 1; On some wiring harnesses it is possible to plug on the big connector off one pin to one side, which brings on all kinds of bizarre things. While this sounds obvious, if repeated in restoration, changing even the whole wiper motor and the switch leaves you in the same place -- not working. Be sure the plug is correctly attached to the switch pins on the back of the switch.
Number 2; Issues with parking are almost always the park cam and contacts inside the motor housing not the wiper switch. Given how hard it is to get to the motor, restoration should include looking in and lubing all this, being sure the park cam action is positive and contacts clean and making good contact. Some Chrysler or Dodge harnesses have plugs that seem to fit but are wired differently end to end (wiper harnesses from other cars) so try to keep all harnesses as they were originally supplied between switch and motor. The cam contacts keep the motor running after you shut off the wipers till they are parked.
What happens: Due to thinking something is wrong with the dash switch (and that is probably not correct) or as part of restoration, someone tries to get the switch out. The twist control knob is held captive by the washer black push button, so that the push button has to come off first. The button is on a very narrow plastic shaft about 3/32 in diameter that runs clear through the switch workings to a separate washer switch added on the back on a 6/32 stud. The shaft is a very fragile thermoplastic (I know this from trying a shrink sleeve to fix, it melts instantly) and the button has a bored hole in back with a tiny metal clip to grip the thin shaft. Over time the clip sort of sinks into the plastic, notches it, and locks on. Pulling on the knob, which pulls on the button, snaps the shaft at the knob outer face, and the button flies away. (I found mine 30+ years later, under the power seat motor).
I had bought 4 "NOS" switches over the years, and when I opened Mopar box later, all had a broken off shaft! So mechanics had put a good switch, but broken button shaft, back on shelf. First attempt at fixing this involved a metal shaft, but the shaft passes trough a hollow rivet at the back that is alive with 12v. = Failure. This brass rivet comes in two diameters, likely there were two suppliers of switch. One had room in ID of rivet to make a splice in shaft one did not.
The solution to making this fix universal was to move the washer switch back a bit to gain room to splice it beyond rivet using 6/32 nuts and washers as spacers.
Third time was the charm. By using fiberglass rod, it is strong and non conductive; for the vacuum switch for 300F, after the work below, use as a stack first the provided two 6/32 flat washers (sometimes three) and the original nut with attached lock washer as a spacing pile on 6/32 stud. Weatherstrip cement is good on this as you need flats of the 6/32 to stay parallel with the prior mount shape to hold / index vacuum switch square to shaft, --- then a 6/32 lock washer (if it fits) and nut secures it. For later 300 with electric switch for washer (white box), 1 flat washer then one 6/32 nut without a built in washer as a spacer is right, then original nut with attached lock washer to hold it. Switches are different heights, do not over tighten anything on the stud, just moderation here. The electric switch (? G, H) fits in place of Trico vacuum if you want to do that. (if tired of Trico fun?).
After removing the wash switch off the 6/32 stud, and the shaft with it, it has to be cut square; careful on measuring, no 2nd chance. For the vacuum switch, cut the shaft with razor knife on a hard flat surface 7/32 from front of housing. For electric switch is it 3/16; then wind 7 turns of .025 SS lock wire provided tightly together around the 3/32 fiberglass -- like a spring; easiest to do with leaving long ends, then cut off with electrical dikes; flatten cut ends against shaft tightly with pliers. Mix a small batch of epoxy on a sheet of paper, with toothpick put a dot on each shaft, put them in contact and slide "spring" over both so it is centered, embedded in epoxy, try to smooth outer part so no blobs of epoxy, set aside to harden, keeping the shaft square by propping it. Check the fit and clearances on back of switch before it hardens. Stainless should not hang up on rivet which would hold the vacuum switch open, and it should allow the switch to be pushed in. The shaft should be carefully centered and straight, over the rivet hole.
Once hard, assemble with spacers in sequence described above; shaft sticks out about .400; put switch back in car. New button provided (machined from Delrin) has oversize shaft hole on purpose, it has no pull out forces in use, so idea is a dot or very short ring of weatherstrip adhesive at very back of button holds it sufficiently to rod to keep it from falling off. After the knob is on, do not fill with it as then you cannot get it off again. The clip is of no use as all different OD sizes now and grips too hard anyway. Later cars might have a longer button. This one is sized for F. If you want to use old button have to remove clip and old rod. A razor knife can grab under edge of it.
If cutting fiberglass rod (supplied one is cut right), you cannot cut with dikes or fine saw as it tends to splinter at last second. I found that sort of notching it all around 360 in a vise with hacksaw fine blade drawn backwards prevents that, and cuts it square.
We have a kit for $35 plus, with all this stuff, except epoxy and 3M WS adhesive. Note that making the button cost that in machining time.
Contact Keith Simons at
for more information.
Hope this info helps.
John Grady PE