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| Gatvol Member Since: 10 Dec 2024 Location: Aberdeen Posts: 1   
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Some Insight into wiper Park Switch by Lucus
So, I came across a really bizarre problem with my TD5 2004 Defender. Some time after installing a new wiper motor complete with rack and wheel boxes, one day, try as I might, the wipers would not switch off. Once they were triggered, either by switching them on or by pressing the screen clean stalk they would just continue to thrash. The situation seemed to deteriorate. First, I was able to get them to park if I turned the ignition off when they were more-or-less at the end of their stroke, in the park position, but after a time this seemed to stop working. Of course, they would stop when the ignition was switched off, but when the ignition was turned on again, they would thrash away. At that stage the only way to get them to stop was to physical arrest them in their park position when all the initiation sources had been cancelled. Looking at blogs and the like it seems that others had experienced similar problems. I had the old park switch, from my previous wiper motor, and replaced the switch but it seemed to make no difference. I replace the wiper relay but that fixed nothing. From the circuit diagram in Haynes, and many blogs on the subject, it became clear that experts did not understand how the switch actually worked, and I could not make head or tail of it. But I came across this link which describes its function in considerable detail. https://www.gomog.com/BLAIR/tech/electrica...Motor.html It is directed at a TR 6 sports car but to quote, ”Although written specifically for a TR6, it is typical for many later model British cars.” What is not grasped by many of the “experts”, explaining the function of the switch, is that it is not simply a switch which cuts power of at a dead-spot, when the button on the rack crown-wheel reaches a specific position. There are 5 wires from the wiring harness and three forward to the wiper motor. From the diagrams in the above document, looking at the 5-pin plug on the park switch, 2 of these pins are switched off and another 2 are connected as the plunger is lifted by the button. I verified this, with a meter, on the old park switch from the wiper motor I removed several months ago. The justification for this is that the switch momentarily puts a reverse bias on the motor to stop it dead, connecting it, not to the battery, but to the residual charge residing on the field windings. That was all very enlightening, but did not end my trouble with the switch. I resolved to order a new park-switch and replace the existing one, happy that I also had another spare from the old wiper motor. I followed some standard instructions for disassembly to access the wiper motor. First task was to pull the blade arms off the spindles. This made logical sense for me, as I had to consider the possibility my wipers might still “run-away” on a dry windscreen. Getting to the wiper motor is not a trivial endeavour, but I have now done it several times and blundered on. Much of the dashboard has to come out. I progressed to the instructions for removing the existing park switch, but noticed that one of the spade connectors appeared to be loose. I pinched it up a tad and pushed it back onto the mating prong. I decided to see whether that could have been the problem all along, reconnected the battery, and tested the function of the wipers. They appeared to work perfectly for both the wash function and the intermittent wipe. The wiper spindles rotated, paused and rotated again and did all the correct jiggery pokery, in accordance with the switch functions selected. I cursed myself for sloppy workmanship and proceeded to start reassembling the dashboard, but night fell, and I had to postpone the work. For some reason, thinking about the job that night I resolved to put the wiper arms back on the spindles before I proceeded, to further confirmed that all would function satisfactorily. I chided myself, as it was illogical to believe the wipers baring in the windscreen might make a difference to their functionality. But that is exactly what happened. With the wiper arms replace the problem reemerged and the wiper now “ran away” once any operating function was selected. While this was illogical it was also a reality. I had to reverse the reassembly I had done the previous day, and then remove the existing park switch. I compared the three switches I now had. The replacement I had bought on eBay was Land Rover part LR057182, which visually appeared identical to the switch I removed. The older switch was dimensionally compatible but one could see it was from a different manufacturer. The travel on the plunger was different on each switch, but the way in which they switched pins was essentially identical. I verified that the new switch would function correctly with the wipers loaded onto the shafts and bearing in the windscreen. I reassembled everything and, touch wood, the wipers now function satisfactorily, and I hope will continue to do so. Reflecting back, I can also now understand why the failure manifested. Just prior to this problem starting, I replaced my windscreen under an insurance claim, and the suppler also elected to replace the wiper blades. I did not associate this with the “run-away” wiper problem until recently. Commenting on what I have deduced from this wiper park problem I can say that some, or all of these factors may be relevant, because they are variables in the nature of the aftermarket equipment we install on Land Rovers, particularly Defenders. These are the variables: the size and thickness of the dead-sector insulator button on the wiper crown wheel, the stoke of the switch plunger and other associated dimensions, the sequence in which the double switching occurs and the drag of the wiper on the windscreen. I suggest, if you replace the wiper motor assembly, recover and keep the park switch from the old motor. I don’t believe you can have too many of those little switches to juggle about with. Please don’t comment that this blog doesn’t make sense. I’m posting it precisely because most of it didn’t make sense to me then and now. |
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10th Dec 2024 3:44pm |
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| Roverdrive Member Since: 11 Aug 2024 Location: Wirral Posts: 15
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Thank you for taking the time to type "War and Peace".
Much appreciated |
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16th Dec 2024 2:59pm |
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