Intermittent Windscreen Wipers

Discussion in 'How To' started by mikedjames, May 23, 2022.

  1. mikedjames

    mikedjames Supporter

    I have a late 73 bus with an early style wiper switch, but hopefully the info here can help others.
    I also have an electric screen washer pump operated by a micro switch in place of the water valve originally fitted.

    My installation goals
    • No additional switches.
    • All wiring in line via connectors so removeable.
    • Prepared to 'lose' fast wiper speed.
    • Wipers should auto park between wipes.

    There are several relays available for fitting to your bus.

    • Aftermarket intermittent relay. A simple relay with a variable pulse rate that switches a pair of relay contacts. Uses e.g. a rotary knob to adjust delay.
    • VW/Audi relay 19 as originally fitted. Fixed delay
    • VW/Audi relay 99 fixed/ programmable delay.
    • vw/ audi 197/198 programmable delay mentioned on the Samba as alternatives.

    More soon.
    Last edited: May 23, 2022
  2. stirlingmoz

    stirlingmoz Supporter

    You have my attention ;)

  3. mikedjames

    mikedjames Supporter

  4. mikedjames

    mikedjames Supporter

    To start off, here is the wiring diagram of the basic windscreen wiper circuit - basically the switch is drawn in a complicated way in the VW diagrams but what it is is this: A slider shorting out adjacent pairs of contacts.

    There are three positions.
    • Fast : 12 volt power from 53a is connected to 53b . This goes to a brush on the motor which is not at 180 degrees on the motor, so the motor has to spin faster before its back EMF plus resistance generated voltage equals 12 volts. This trades speed for torque. Mine did not have enough torque to start on a dry windscreen with the current going through the switch.
    • Slow: 12 volt power for 53a is connected to 53. This goes to a brush on the motor at 180 degrees to the earth connection , this gives maximum torque but limits the speed to about 1/2 the speed of the fast speed.
    • Stop: 53 is connected to 53e on the switch. This goes off to the rotary switch on the gearbox of the wiper motor. This provides 12 volt power for the motor until the position is near park. Then it disconnects the power and when the gearbox is in park position, it shorts the motor out, braking it.
    The fact that the motor is shorted out when the blades are in park position is the reason a lot of attempts to play with the wipers result in blown fuses.
  5. mikedjames

    mikedjames Supporter

    Using a Relay 99 from eBay - this was £12 + £3 postage (June 2022)

    So to begin with, here is a re-draw of @snotty 's wiring for the intermittent wipers.

    It features
    • Passes current through wiper switch
    • Not parking on intermittent wipe cycles as park wiring only used in Off position of switch as original

    • Fast operation as before on position 2
    • Slow operation as before on position 1
    • Intermittent operation on position Off, using extra switch which will give either :
      • one wipe every 4 seconds - just flip switch on
      • programmable wipe - flip Intermittent switch on, turn off for delay then turn Intermittent switch back on
    • Parking when switch turned to off
    • Wash/wipe cycle when Washer Switch button pressed in off position, parking after wipe.

    Last edited: May 29, 2022
  6. mikedjames

    mikedjames Supporter

    This was my version of the circuit : after some testing I discovered that if you held 12 volts on pin T of the relay, it continued to operate the wipers continuously (I still need a longer period of rain to fully test this mode).
    This variation uses the logic of the relay to operate the motor, apart from the parking switch which is still used as before.
    • Does not pass current through wiper switch
    • All wiper operations end in parking

    • Normal speed operations in position 2
    • Intermittent operations in position 1
      • One wipe every 4 seconds, move switch from Off to position 1
      • Programmable wipe, move switch to position 1 briefly, return to off for desired delay, move switch to position 1.
    • Parking in off position.
    • Wash/wipe cycle when Washer Switch button pressed in off position, parking after wipe.

  7. It makes perfect sense ;).

    Triggering the changeover relay in the unit puts a quick dab of +12V on 53M to get the wipers moving, then immediately drops back so that the park switch wiring is as it's supposed to be. After a single sweep, the wipers park nicely.

    'Tis the way VW did it, and aftermarket delays I've seen. You've got to switch the 53 line, or you'll be blowing fuses.
    matty likes this.
  8. Never really looked at this as I have a dash mounted hella unit to do intermittent but on our year of bus there is a down position with a little white plug to stop you moving the stalk in that direction. I’d always assumed that position would, or might provide a feed for an intermittent set up! Originally when I fitted the hella rotary switch I anticipated seeing if that position would be able to switch it on and off and use the rotary switch fir adjusting the timing of the sweep?

    In any case it’s s very worthwhile mod to have intermittent. Coupled with the use of Rainex I hardly ever have the wipers fully on!
  9. mikedjames

    mikedjames Supporter

    There is also the very simple intermittent relay circuit off eBay.

    Yes, I think I misinterpreted the way it worked in the Position 1, where it just connects the power as usual, whichever way the relay is positioned.
    The intermittent operation overrides the Off position with single cycles going back to park.
  10. mikedjames

    mikedjames Supporter

    99 Relay Basic operation
    All of these circuits are based on the 99 relay which has the behaviour that when neither I or T are at 12 volts, 53m is connected to 53s.
    The relay is triggered by:
    • "I" being switched to 12V permanently or by the programming sequence of a quick dab on "I" followed by a programming gap to copy, followed by "I" being held at 12V permanently until you want the wipers to stop.
      In this case it pulses the relay on, connecting 53m to 15, until it detects the voltage on pin 53s going to 12 volts, at which point it "knows" the wipers have moved from the park position, so it switches the connection back to 53s, then delays for the programmed period when it repeats the connection to 15, waiting for 53s to go to 12 volts and so on.
    • "T" being switched to 12V permanently, the motor will run, with the relay being held connected 53m to 15 until you let "T" disconnect, at which point it will wait for 53s to go to 12 volts then switch the relay back to 53m to 53s being connected.
      The wiper blades then park.
      There doesnt seem to be a time limit here, it seems to repeat a single cycle forever if you hold "T" at 12 volts, only parking when "T" is disconnected.
    Wiper Switch - the mystery position
    After more experimentation, I find that my wiper switch has four positions, but two of them simply are park positions, the shorting connector bar just connects the parking power to the 53 motor connection. My switch has lost the plastic wedge that blocks this position
    Last edited: May 29, 2022
  11. Some switches (including mine) seem to have the plug missing, so you have stalk position that does…nothing.
  12. Mines like that as o removed it and lost it
  13. :rolleyes:
  14. Taking "I" to +12V starts the intermittent wipe function. The wiring for the wiper switch in slow or fast will override the intermittent function by proving +12 to the motor in parallel with the intermittent relay. Taking "T" up to +12V (from the washer switch) starts the short period of four or five wipes when you operate the washer pump.
  15. mikedjames

    mikedjames Supporter

    I think that with the '19' relay, 12 volts on the "J" connection causes a simpler repetitive connection of 15 to 53m every 4 seconds. Basically a slow flasher unit in its earliest incarnation, with the flasher being activated by 12 volts on the J connection.

    The wash/wipe on later buses uses a more complex switch where the washer operation also disconnects the parking connection from 53 and connects it to 12 volts briefly.

    If you only have a simple relay which has a single contact, putting it in series with the black wire will cause the slow speed operation of the motor (and parking) to become intermittent based on the motor stopping all the time that the relay is activated and the normally closed contacts are opened.

    Ideally what you need is a relay that does the same as the 19 or 99 relay, and briefly disconnects the black wire and connects the motor to 12 volts as the relay pulls in.
  16. mikedjames

    mikedjames Supporter

    The "T" staying at 12 volts actually starts an indefinite sequence of those 4 or 5 wipes, you can hear the relay clicking briefly periodically as it gets "cancelled" by the voltage reappearing on 53s, and then immediately restarting the sequence. Hence my cheat of using the fast position on the wiper switch to "keep washing the screen but with the washer pump turned off"

    One other aim of my "different" wiring was that I noticed that my wiper switch was partly responsible for slowing down the wiper motor by being worn and blackened inside. I stripped mine down , cleaned the contacts and brass slider , and everything went faster. I also refreshed the cable tie holding critical parts together.
    So I decided to go for a solution that just like a hot start relay , no longer passes current through the wiper switch.
  17. “T” will keep the wipers going for as long as you operate the washers.
  18. scrooge95

    scrooge95 Moderator and piggy bank keeper

    If anyone works out how to make that position into an intermittent option, I'll happily remove my plug! (and pay the person in question to make it all happen... wiring diagrams are a foreign language to me)
  19. I have plug envy...

    You may find in the unused position, there aren't actually any contacts in the stalk switch, mean buggers :(

    Could do it with a separate switch on the dash and an intermittent relay. Easy, for a person of your skills :thumbsup:
    scrooge95 likes this.

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