I had another play with my spare 850 wiper motor and a multimeter today, to see what speed I could get from it.
I have an ex-Fiat 124 Sport wipers 0-68 ohm variable resistor wired into the field circuit.
0 ohms gave standard speed, increasing it up to 22-27 ohms gave more than a 2x speed increase.
At 35 ohms it was no faster than at 27 but had insufficient torque to start.

So....
If you want 2 speed wipers here's what to do:
1. cut one of the field wires and solder some 2 core flex to the 2 cut ends.
2. run the flex out to an on/off switch.
3. wire a 22 or 27 ohm, wire wound 10W resistor across the switch too.

With the switch ON you will have standard speed, with the switch OFF you will have approx 2x standard speed.

BTW I didn't just make this circuit up, I copied it back in 1967 from a Popular Mechanics? magazine, it worked in my 850 back then too.


Why does it work? I'm not an electronics guru so I don't know, but it does.

<edit> typos- I had ON and OFF arse about.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thats awesome Doc, just what ive been looking for and saves having to do a conversion, very handy howto

we'll do a little more work on this and make it into a "How to"

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Stop Licking the Dog...I Don't Care Who Started It

Why the resistor would make the motor twice as fast I don't know (Would suggest a relay in the circuit so the factory switch doesn't take twice as much current), but when the switch is ON the circuit takes the path of least resistance, so thats why things are normal again.

The current draw is actually less when the motor is running fast.
I know how the switch works (it shorts the resistor), what I don't know is why adding field resistance speeds the motor up.
Mick, where are ya buddy...

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Adding resistance to the field would send more power to the armature, so it spins faster, but if the current is less, then there should be less torque as a result, or something. I'll shut up now and wait for a sparky.

your right - more resistance = higher speed,

i cant explain right now as im sleepy lol..... and would have to read through some of last years notes

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backyard performance............. Aint it the best