Wiper motor switch swap issues 73 GT vega

[gt350fme]

I am trying to use an aftermarket wiper switch but there must be something I am missing, unless I am mistaken there are only 3 wires and all are grounds, 1 ground links the other 2 grounds that go to the wiper motor to complete and ground circuits slow and fast.
Problem is the aftermarket switch will only support the fast mode and the slow mode just won't function.
Is there something in the stock switch that the aftermarket switch does not have like some resister or something?

Painless universal wiper switch is what I'm trying to use, I have a pic of the switch poles on my iPad but it's too big and won't post, I will have to get one onto my pc and post it.
Any ideas would be appreciated

GT

[bugdewde]

Sorry, I don't have any info for you..... but I'm subscribing to this thread because I have the same issue in my '72 Kammback. I'll swap on a stock switch soon to see if that is the issue. I'm betting it is.

[gt350fme]

I have concluded that this universal 2 speed switch will only support one speed because the 1 and 2 switch positions don't combine together at the same time ever, and they need to in one of the positions for slow speed to work, A and AB not A or B.

Unfortunately vender info from my internet searches for a universal 2 speed wiper switch don't specify if any positions link together, so I have some more research to do.

[zeke]

GM should have labeled the terminals "run" and "low" instead of "hi" and "low", would have avoided a lot of confusion.

High speed grounds the high terminal only, low speed grounds both.

Off shorts both terminals to achieve low speed park via the internal park switch.

[zeke]

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[gt350fme]

Thank you Zeke for shedding some light on this subject for future reference.

Turns out that wiper motor # 40-140 for the h body was also used in many other GM cars from the mid 60s through mid 70s, and the stock round switch from this time period is a match.

[zeke]

NP man. I think it was around 1985 - 86 that GM changed the control to an actual hi/lo setup. (one terminal grounded for either operation). Any switch from the 70's should work.

[ir_efrem]

Old topic, but I thought I might add my $0.02 here for possible switch replacements.

Lets label the switch connections with arbitrary numbers

1 - Ground
2 - Washer pump +12v
3 - *Low speed +12v
4 - *High speed +12v

* yes I know that 3 and 4 are together for actual low speed and there are resistors involved in the circuitry.

Anyway purchase a universal wiper switch with 4 positions. 1 for off, 2 for washers, 3 for Low speed, and 4 for high speed.

Add 2 Schottky Diodes (in parallel) with the Anode on 4 and Cathode on 3. I use 2 diodes because it drops the Diode voltage loss in half. At this voltage and amperage, 2 general purpose Schottky Diodes will have a voltage drop of .1 or .2(ish). I would say to get 2, 60v 10a Diodes. The SBM1060LSS_AY_00001, from Digikey.com is exactly what I would use. They cost $0.31, order several just because Diodes are handy and they are going to charge you like $7-$10 for shipping anyway. Do NOT cheap out and buy some unknown brand from Amazon or Ebay. Just spend the money in shipping and you will know that you are getting a name brand quality part (you have been warned).

When switch is in position 3 voltage will flow from wire 4 to wire 3, then to ground, through the switch. This activates Slow wipers.
When switch in is position 4 the diode blocks voltage from back feeding into wire 4 from wire 3. This activates Fast wipers.

I'll be doing this exact modification to my 80 Monza. I will report back.