[TheMonkey]

Rebuilding my 61 dual speed wiper motor. Connector to wiper motor has 3 prongs. Middle one is the power to the unit from ignition. Bottom one is the high speed grounding switch. Top one is the low speed grounding switch (although both bottom and top must be grounded for low speed to work).

The low speed connector has a heavy ballast resistor just inside motor enclosure going from connector directly to ground strap.

I *think* that resistor has gone bad on my unit. Low speed on bench test is not working and seems to be tripping a circuit breaker or something else not so good. The resistor only shows 4.4 ohms resistance. I'm thinking I need to solder in a new resistor.

Can anyone confirm what the resistance of this should be? It's not in the 61 manual. I'm not sure what years cross eachother, but I suspect specs should be similar for several years.

With plug pulled out, just check resistance from pin 3 (top pin) to case ground. Or can check resistance with plug in if switch is turned to off.

Thanks, Scott.

[TheMonkey]

little more fooling around.

functionally... low and high speed seems to working okay. it's not circuit breaking in low speed like i thought it was. i must have done something wrong on the bench.

but.... in high speed, the resistor on the back of connector plate gets hot and starts to smoke. in low speed, it cools down.

it's possible that some oil got soaked on it and that is what is causing the smoke when resistor gets to normal operating heat in high speed?

hmmph. just don't want a fire ya know?

[TheMonkey]

In the following diagram, the lower connection is the low speed ground circuit, which is the 'upper' connection when mounted in car.

[Stuart]

Here's what I measured at all three terminals on mine, from top to bottom (one probe to the motor housing, the other to the terminal:

14.7 ohms
2.5 ohms
30.3 ohms

[TheMonkey]

Thanks Stuart.

[Stuart]

OK, it cooled down some so I went out to the garage for another look.

I unhooked the connector, but unfortunately the screw holding the ground strap to the body is hidden down behind my tripower manifold. As a result I wasn't able to get a decent grip on it with a screwdriver so I left it connected.

The top terminal still reads 14.7 ohms to ground (measured either from the case of the wiper motor or from the ground strap.)
The other two terminals are open circuits, with infinite resistance.

I then dug out two other wiper motors from a junk box and checked them. Both of them had a reading of about 20 ohms or so to the top terminal, with infiinite readings to the other two terminals. Now, I'm not sure exactly what cars these two are off of...they're both from Pontiacs but I don't remember what years. They look as though they have the same mounting bolt pattern but the electrical terminals are oriented differently - one has them sticking straight out and the other has them laid over flat to the wiper casting. These two both have washer pumps on them, which may be why they look different than the one in my car which doesn't have a windshield washer.

[TheMonkey]

Thanks Stuart-

I think I may have something wrong with my 'Shunt F' circuit or 'Series F' circuit - as seen in the diagram above. When the motor is off, the 'relay coil' is closed. So, when you measure from low speed ground pin (top pin when mounted in car) to ground, it can be either:

1) ground strap unhooked from case, measured from pin to case = 'Shunt F' & 'Series F' in series
2) ground strap unhooked from case, measured from pin to ground strap = 'Ballast Resistor'
3) ground strap hooked up to case, measured from pin to ground = both of above situations measured in parallel.

'Shunt F' & 'Series F' are inside the motor housing.

On your spares, you measured:

pin -> ground case at 20 ohms. Was the ground strap connected to case? Measurement can be made to only ground strap if it is not leaning against case where it enters - leans only against the circuit board.

Mine are:
Situation 1) 5.3 ohms
Situation 2) 20.3 ohms
Situation 3) 4.3 ohms

This foots with resistance calculator (inverse of (sum of inverse))

For reference, the brass ground strap is the circled link in the diagram:



I really appreciate the help, thanks.

Scott.

[Stuart]

I went out and looked at the loose wiper motors again and it turns out they don't have ground straps on them at all, so I don't know what the deal is. Upon closer comparison with the one in the car their casting are configured somewhat differently so they must be from some other year Pontiac.

[TheMonkey]

Okay, thanks. But there still might be enough info to make some kind of conclusion.

When in low-speed mode, the ground is made direct through the switch, and no meaningful current would go through the resistor even though it's there. When in high-speed mode with smoking resistor, the ground switch is opened, so the current from 'Shunt F' goes through that resistor (which it is supposed to).

My middle power pin has 12.1v (wiper motor going)
Voltage at low-speed pin (wiper motor going), low-speed switch open - not grounded is 9.4v.

So, the voltage drop across the 20.3 ohm resistor is 9.4v, which would be 0.46 amps. or 4.3 watts.

Maybe there is just too much current finding it's way through 'Shunt F'.

I guess if you (or anyone) get a chance, could run dual speed wipers on high, and measure voltage at the upper pin (low-speed grounding pin), and voltage on the middle pin (should be 12.x volts, but good for reference).

[TheMonkey]

Well.... I think I might have it.... ready to move on anyway.

I cut out the resistor, and replaced with 2 each 10 ohm resistors in series (10w each). Everything seems to work okay now, and the speeds seem to be okay although I'm not sure how many wipe cycles are supposed to be for each speed, but looks pretty good.

The resistors I put in get too hot to hold them - prob 200 - 220 degrees while in high gear, but the wattage of the resistors should be sufficient. The motor case gets a little warm after awhile directly at the end of the case where the brushes and end bearing are - but not hot.

Anyhow, I'll just assume that the original resistor had correct resistance, but just got too old and brittle to dissipate heat. I'll move on - and hopefully no fires.

Everything painted up and installed. Very buttery.