Slow Car Fast
December 21, 2010 - Time to wire up the wipers.
This should be straightforward, right? Well, no. Things started off easily enough, with one wire for low speed and one for high speed. I'm not exactly sure how to duplicate the intermittent setting, but that's no big deal.
But the Lucas wipers have an extra wire that is for the parking function, to return the wipers to home base if you turn them off halfway through a stroke. It's a 12v signal that is fed back through the low-speed circuit until the wipers are parked. I've been inside a Lucas wiper motor and it's a reasonably intelligent way of doing things mechanically in my opinion, but the problem comes from the fact that there's some switching that needs to be done inside the wiper switch. My Miata wiper switch doesn't have this internal logic. So I need to find some way to have the park wire connected to the low speed wire when the wipers are off, and disconnected when they're on. That's easy enough to do with a relay...except for the fact that I have to have the high speed setting do the same thing.
Finally, after a bit of scratching around, I figured a way to do it with a relay and a couple of diodes, without passing the load from the wipers through the diodes. Out came the soldering iron and it all went together well. There's still one odd behavior, the wipers move fairly slowly in "park" mode even though they're seeing full voltage and theoretically full amps. I'm not sure what's happening there, as I'm pretty sure they worked well before the relay went in. I'll revisit it tomorrow to see what's going on.
I did manage to get the squirter working today, and discovered that it's aimed in completely the wrong direction much to my amusement. As a bonus, the Miata wiper switch includes some logic that swipes the wipers three times after you trigger the washer. Excellent.
Oh, and horns now work as well. Meep meep!
entry 517 - tags: wipers, electrics