[TR] TR250 Windshield Wiper Motor and switch

Greg Lemon glemon at neb.rr.com
Sun Jan 11 07:12:28 MST 2015

I don't think they changed the wiper motor from the TR4a to the TR250, it is 
still the old square body 2 speed with three wires coming out, I couldn't 
tell the colors on mine either, they were too faded, not being an electrical 
guru, I think I just played with the wiring until it worked right, but 
Randall's instructions would have a lower risk of making sparks and smoke.

Greg Lemon

From: "Randall" <TR3driver at ca.rr.com>
Sent: Saturday, January 10, 2015 11:17 PM
To: "'Roger Elliott'" <elliottr at rmi.net>; <Triumphs at autox.team.net>
Subject: Re: [TR] TR250 Windshield Wiper Motor and switch

>> On page 133, he mentions that for high speed operation "Both the
>> terminal 'S' and Terminal 'F' of the dash switch have been shorted to
>> ground."  But the diagram on page 134 for high speed
>> operation seems to
>> show current through the ground and one of the other terminals on the
>> switch.  I would have though with both terminals shorted to
>> ground there
>> would be current through both wires to the switch.
> In effect, there are two coils inside the wiper motor.  For low speed, 
> both coils are in series and there is only one ground through
> the wire marked R/LG on Dan's diagram.
> For high speed, the junction between the two coils gets grounded.  So, one 
> coil gets full battery voltage, and the other gets
> nothing.  In effect, it no longer matters whether the R/LG wire is 
> grounded or not, there will be no current through it either way.
> It just so happens that the switch does ground the R/LG terminal, but it 
> doesn't need to.
>> So, I was wondering, do I need to connect both the R/LG and N/LG to
>> ground to test if the fast speed is working?
> No.  As above, when the N/LG is grounded, it doesn't matter if R/LG is 
> grounded or not.
>> One more question.  The three wires going into the motor all
>> seem to be
>> the same color.  How do I know which should be hooked to
>> which wire in
>> the harness?
> Run the motor until it is partway through a cycle, then disconnect the 
> power and use your ohmmeter (DMM on ohms X1 scale) to
> determine which contact is grounded to the housing.  They will all show 
> some continuity, but one should have a much lower reading
> than the others (roughly the same reading you get if you short the probes 
> together).  That is the R/LG terminal.
> Now measure the resistance from that terminal to each of the other two. 
> The one that shows the highest resistance will be the G
> terminal.  The remaining terminal is N/LG.
> I don't have one handy to try, but it is possible that the speed 
> difference does not show up unless the motor is loaded.  And the
> difference is not particularly large anyway, only about 20%.  If your 
> motor runs when either terminal is grounded, you will probably
> see the speed difference when you get the wipers connected.  If not, there 
> must be a short between the two terminals inside the
> motor.
> It's a shame Dan didn't provide resistance measurements.  Perhaps someone 
> else can.  (I only have the earlier style 2 speed motor,
> which may not be the same as the TR250.  And it's buried in a box 
> somewhere.)
> Randall
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