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Re: Make that rear wiper work right![200/85] posted by Martin T on
Sunday, 14 February 1999, at 6:18 p.m.
The front and rear wiper relays may look the same (but the front relay should be black while the rear one is yellow, though) but you cant swap them.
The difference isnīt related to the load - itīs all in the construction of both the relays and the wiper motors. The front motor has got two more connections than the rear one which in fact is a really simple construction with only one positive terminal. The front one, however, has got an internal sensor which will return a ground signal, I think, when the wipers are in the "parking area", i e in the lower part of the windshield.
The front relay uses this signal for internal timing - when using the itermittent function the relay switches on each cycle exactly as long as the sensor "feels" ground (you could here the relay "click" on and off). This is because the wipers should be able to leave the parking area. The rear relay works different because itīs supposed to give more than one single "wipe" per cycle, normally three wipes. In that case, the relay doesnīt have to relate to the wiper location - it just turns on for a few seconds, and then shut the wiper of.
Iīd guess this function was implemented because of the incredibly sleepy rear wiper on the pre 84 models - the newer ones are greatly improved, and uses a relay which will only produce single "wipes" in each cycle. But the "ground" sensor isnīt there and thatīs why the front relay doesnīt work as supposed to.
--Martin T