TR2/3/3A Electric to Wiper motor TR-3

I have four TR-3 wiper motors (2 on cars, 1 parts and one for the car I am restoring. All have two terminals marked 1 and 2). Wiring harness and electrical diagram all have two wires. BUT on the one I am about to install there is a third terminal marked E. Using an ammeter it appears to ground the casing but does not show continuity to either terminal 1 or 2. Power to one either terminal 1 or 2 and ground to the other of those two and the motor runs. What was terminal E for? Only thing I can think of was maybe it is where you'd ground a windshield washer fluid pump. Tom

'E' does indeed stand for 'earth' or ground. What it does is complete the circuit when the motor is parking. For approximately 3/4 of the motor's total motion, you should see continuity between E and terminal 1 (and a fairly low resistance, which would probably show as continuity, to terminal 2).

If it doesn't, then your park switch is not assembled (usually have to remove it to remove the rack, so it's generally not in place when the motor is on the bench) or isn't doing it's job.

It sounds like you have a DR2 motor which is used in the Austin Healey 3000 and has a self-parking feature as described by Randall. You can use the motor without the self-parking feature, but you may have to experiment with which ground to use, otherwise it may never shut off when you turn the switch off.

Starting at TS12568, the TR3/A/B also used the DR2 with self-parking (unless the rare 2-speed wiper option was fitted). Apparently some had the 'E' screw and some did not, but they all needed to be grounded for proper operation. (Although I have seen them work from being grounded through the wiper linkage, it's probably not a good idea.)

Sorry for the poor quality, this is the best photo I could find at the moment. If you look closely, perhaps you can see the ground screw and the wire to it, near the two main terminals.

Just to add more info, the DR2 in the Austin Healey has the hot lead powering the motor all the time. The dash switch is wired to ground, so the circuit to ground is interrupted by the turning the switch off. The 2nd ground goes to the self parking mechanism. It overrides the switch when the metallic portion of the self-parking mechanism is in contact with the ground wire. There is a portion of the self-parking mechanism that is non metallic and that is where the motor will stop -- hopefully at the base of the windshield if it is adjusted properly. For this to all work properly, the motor must be insulated from ground -- hence the use of rubber mounts.

TimK said:

For this to all work properly, the motor must be insulated from ground -- hence the use of rubber mounts.

Click to expand...

That's odd. On the TRs, the motor is grounded (the 'E' screw goes directly into the case), and the park switch completes the circuit between a wire from the #1 terminal (visible as a loop of white wire in the photo above) and the motor case. Otherwise it works as you described, terminal #2 has power whenever the ignition switch is on, and the dash wiper switch grounds terminal #1 to make the motor run. When the wipers are away from the 'park' position, the park switch also grounds terminal #1.

Is the motor hard mounted to the body or does it have isolating rubber mounts?

Rubber grommets at the mounting bolts to the bracket. You can see 'em between washers in Randall's pic. At th' base where the gearbox is attached to the mounting bracket.

The assembly is mounted through rubber grommets.
"E" is a lug held in place by a long bolt that screws into the case.
John

The self-park feature is not documented very well. Most of the wiring diagrams I have show power coming from the switch, not going to the motor first so the switch (or self-park switch) can complete the ground path. Perhaps that's how the original (no park) and 2-speed motor was wired.

However, a year ago I thought I'd finished a small portion of my restoration, when Randall noted that my self park function should work. After taking the motor apart another um-teen times, it should work now (once I have a functional car to attach it to). The self-park wire was broken inside the unit, and the wire/insulation was in need of replacing anyway. It's a PITA because that wire is soldered to a lug on the cap (that can rotate for adjustment) and the other end is soldered to the winding/brush assembly (lug #1). The wire length is only about 6", but passes through the housing, subassembly frame and gear cover. The gear cover is an illusion, and one would think it didn't need to be, until you try to assemble it.

When the E terminal is connected to ground, it connects the assembly/case to ground, allowing the self-park switch to function. The rubber mounts are not to eletrically isolate the unit/case from ground (though they do). Maybe for noise isolation ?! Both motor terminals are isolated from the case.

Now that my unit self parks, I can park it and move on to more important things... Thanks for pointing out what was not so obvious.

In case anyone is interested, there is a wiring diagram showing the correct wiring for the self-parking TR3 wiper motor at
https://i258.photobucket.com/albums/hh260/TR3driver/TR3ALHDSCHEMATICMODIFIEDFROMPRAC-1.jpg

(Click on the image to get the full-size view, I can't seem to figure out a direct link.)