Ken, a while back you answered a thread about wiper problems and outlined the voltages at the different terminals of the wiper.Wiper switch not working on a '74.
With the key on I have power to the centre wire of the wiper plug...in high speed position I have power to one other terminal... in low speed nothing changes, low wire does not get hot. I can push and hold the wash position and the wipers will work in low speed.If I take the plug of the back of the switch and jumper from hot side to middle wire, wipers operate in low speed. Never did get them to come on high speed. I'm thinkin' bad switch.Am I right??
Thanks in advance. You always seem to come thru.
Phil

I'll try to never let anyone here down.

When the key is on, the ignition supplies power to the wiper motor. There are three wires between the motor and switch. (Not counting the washers) The switch supplies a ground from the motor when turned on.

It grounds two wires for low speed, and only one wire for high speed.

The colors may be off, but I think the high speed wire is gray, and the low speed is purple, and the ignition hot is white. I could be wrong on these.

When you ground just one wire, the motor runs on high speed. The second wire is added so two of them are grounded you get low.

If we just reduced power to the wiper motor to slow it down it would lose power, and may not move debris from the window. So the low speed wire supplies a reverse shunt that causes the motor to slow, with full power on the high speed, which slows the motor but keeps full power. Oddly enough, this means the wipers use more power on low than they do on high.

The wiper motor must be grounded at the motor to operate. This is due to the park position switch and internal operation of the motor.

Keep in mind, with the switch off, there will be power at the motor wires, they are an open circuit on the hot side, so voltage will be there, but there is no amp flow. A test light would be on.
When the switch is closed the voltage goes to zero, and will show no power, but the circuit is now active and flows amperage. The test light will go out.


So bottom line.
1. Make sure the motor is grounded.
2. Turn on the key, wipers off, and check for voltage at three wires.
3. Turn on the high speed, and see that one wire lost voltage.
4. Turn on the low speed, and see that two wires have lost voltage.

If you don't lose voltage, check the switch and switch ground and wires.
If you do lose voltage and everything checks out, the motor is the problem.

These test are only good with everything connected.


Now here is the kicker. Some GMs do supply hot leads from the wiper switch, instead of ground. But evey thing else is the same. One constant hot, one more hot makes high speed, another added hot makes low speed, but turning on the shunt.

I'm not sure which way you car is. I'll see if I can find it if you need me to. But it should not be too hard to figure it out with a good test light.

Let me know.

|UPDATED|4/21/2004 3:13:49 PM (AZT)|/UPDATED|

Thanks Ken for the speedy response, however now I don't know what I've got.

- First off, there's a good ground going to motor
- As mentioned before, wipers will work if I press and hold washer button
- With key on and plugs removed from motor and switch, I have 12v on one term of each plug

With key on and both plugs attached,
1)-switch off-gnd on 1 wire
-12v on centre wire(this is the one hot with both plugs off)
-12v on other wire
2)-switch in low pos
-30 ohm on one wire
-12v on centre wire
-12v on other wire
3)-switch in high pos
-gnd on one wire
-12v on centre wire
-12v on other wire

At the switch plug (both plugs attached,key on)
1)-switch off
-12v on one wire
-gnd on centre wire
-12v on other wire(this one is hot with both plugs off)
2)-switch in low pos
-12v on one
-30 ohm on centre
-30 ohm on other
3)-switch in high pos
-12v on one
-gnd on centre
-45 ohm on other
Just looking at this now, how can I be getting 45 ohm on wire that has 12v with both plugs off?

Just to throw a wrench into all this, if I wiggle the plug at the motor I can make the wipers work low speed, even with the switch off.

I realize this is difficult to figure out long distance, and would understand if you told me to "sod off"
Thanx again
Phil

I'm going to print this, digest it a bit, then get back to you.

Looking at this really has me wondering. Why Ohm readings and volt readings? An Ohm meter cannot be used on a live circuit, or it will lie. It must be used on a dead circuit. Volt is from a live circuit. Were some of these test mixed? Some were with connections made and some without connection. Sorry but I'm a bit confused. I'm sure you know what you did, but I'm not following. That's the disadvantage of long distance.

So let's start over.

What I am outlining is for a non-delay wiper system. The delay is similar, but there is more to it. I dug out a wiring diagram for a 79 C3, but all the C3s are the same color codes, etc. This should work for your car.

This is a bad assumption, but we will for the time being assume all connections are good for the sake of description. More on bad connections later.

There is a white wire from the fuse box which is hot with the key on. This powers up the wiper system. It also splits off to power the washers.

There is a plug for the washers with two wires on the washer motor. One is the white hot lead, the other pink wire goes to the wiper switch. When you push the washer switch, the washers are grounded and activate.

The wiper motor has a three wire plug. These include the white power wire, the gray low speed wire, and the purple high speed wire.

Again the white is hot all the time. The other two should also be hot, due to the fact they are connected through the motor, but are not grounded. The purple and gray go directly to the wiper switch.

When the wipers are turned on high, the purple wire becomes grounded, so voltage is flowing, but the voltage drops to zero, and a test light will go out. The gray is not grounded and still shows voltage, and will light a test light. When the wipers are turned on low, both the purple and gray are grounded through the wiper switch and voltage is zero, but there is current flow.

Due to the park postion switch in the wiper motor, the motor must be grounded to operate. This would make you think the wires become hot to operate. No so, they become grounded.

With the wipers off, you may only have power on the white and purple, the gray may be grounded at the wiper switch. Remember there is park position switch inside the wiper motor. The wipers won't run on low unless the purple high speed wire is grounded. This is the main wiper motor ground. The gray grounds an additional shunt so the wipers will operate on low speed.

Here are the wiper switch wires.
Gray, from the low speed at the wiper motor
Purple from the high speed at the wiper motor
Pink from the washer pump
A smaller gray for the dash light
and a Black ground wire. If this loses it's ground, nothing works. All of these work by grounding them, through the switch.

If you have bad connections you may not get the drop to zero. You can find this with your test light by finding power on one side of a connection, and nothing on the other. But this connection could be at the switch, in which case you would show power through the entire circuit. It's not grounded. Keep in mind the internal switch in the motor.

If you disconnect the wiper plug it can get confusing due to the fact you have the internal switch. So the only testing you would want to do is check the wires to the switch. Connect your test light to a hot lead, and touch the disconnected plug from the wiper motor, and operate the switch. Each wire should respond when you operate the switch in different positions. You can do this test with an ohm meter. One meter lead on each the wires, the other on ground. Don't test the white wire this way. It's the hot lead. If the key is off you will get a feed back response which will only confuse you. Just look for power on the white wire with the key on.

Operating the wipers with the washer switch is good information. When the washers are activated, the washers also have a switch to ground the wiper motor to operate the motor for several swipes to clear the window, then they shut down. This means the motor is okay. So we know the problem is either the dash switch, the wires and or connections, or the park switch in side the motor assembly. This park switch can be replaced without replacing the entire motor assembely. It does require removing the motor doing some soldering. The three wire plug on the wiper motor goes to the park switch. You can see this when the washer pump is removed.

When the washer pump is off you will also see a plastic cam under the pump cover. This must be turned to line up with a hole in the cam and a hole in the pump cover and held in place with a pin, drill bit, cotter pin, etc. This holds the cam in the correct position when the pump cover is reinstalled. The wiper motor must be in the off/parked position when installing the pump cover. If it's not aligned correctly, it can be noisy, erratic, or inoperative.

Give it another shot. Test with everything connected, unless you are testing the switch by itself with the motor unplugged.

Let me know what color wires do what when you are testing. If it has delay wipers we have a bit more to check.

I would take a close look at the connections for bad contacts or a shorting wire at the plug, perhaps under the washer cover, due to the fact it changes when you wiggle it.


If anyone cares, I added a picture of me in my car. Just click on my link in my sig. Not a good pic, my daughter took it. (I made her give it back )

|UPDATED|4/24/2004 10:55:52 AM (AZT)|/UPDATED|

O.K., thanks again Ken. It's supposed to rain yet again tomorrow so maybe I'll get a chance to work on it again and double check my readings.
BTW it is not a delay wiper.
If this doesn't work I'll probably leave it for now as I don't drive it in the rain anyway!
Just hate to have something beat me.

Phil