Quote:
Originally Posted by HarryM1BYT
My take on this, is that the wipers can be controlled by either the BCU or directly by the stalk switch.
Either source could be forcing the wiper relays on and the wipers to run.
He suggests he has unplugged the wiper stalk, so that only leaves the BCU generating the 'run' signal, or a fault on the wiring.
He might try unplugging the BCU, after disconnecting the battery, then reconnecting the battery to see what the result is.
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According to Haynes's circuit diagram of the wiper switch, the wiper switch sends signals to the BCU exclusively, and only the BCU controls the 2 wiper relays. These signals to the BCU are very low currents, and are, as such, susceptible to dirt and damp issues.
The only slight complication is that the washer switch ALSO directly powers the 2 wire washer pump by grounding one connection of the pump. The wiper connections generally stay within the cabin, avoiding road dirt issues.
However the washer pump connection extends to the washer bottle, which is in one of the most exposed areas of the car to dirt, just behind the front bumper. This makes the washer switch connection to the BCU very susceptible to dirt and damp issues, causing false activation of the wipers, while NOT activating the washer pump.
To summarize, a small amount of dirt and damp on the washer pump connection exposed behind the front bumper, CAN cause the wipers to operate uncommanded, while having NO other symptoms or effects. Be aware, if your wipers run uncommanded.
On a new point, one of the advantages of the design of the R75, is that under most circumstances, loads are switched by "intelligent" switches, that helps to protect the load under abnormal situations, prolonging the life of the electrics, and our cars.
The washer pump is a rare exception, being protected by only a 5A fuse (F9).
I must get a better circuit diagram than Haynes.