MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Wiper Switch Wiring

Rebuilding the wiper switch on my 1968 MGB. Can someone tell me the wires that are making contact for the positions of PARK, LOW SPEED, and HIGH SPEED?
(I am working with the following 4 wires:
Blue/Light Green
Red/Light Green
Brown/Light Green
Green

I'm o.k. with the Light Green/Black and Black ground for the washer switch AND the white and yellow for the overdrive switch.
Thanks!
Eddie
Eddie Haynes

Blue/Light Green is Low Speed
Red/Light Green is Park
Brown/Light Green is High Speed
Green should be the power feed from the ignition via the fuse box. This should also go to the motor.

I keep directing folk to Paul Hunt's amazing web resource for MGBs. He has a full description of how the wiper works here http://www.mgb-stuff.org.uk/electricstext2.htm#wipers
Mike Howlett

Thanks, Mike. I appreciate the info. This is what I need.
Eddie
Eddie Haynes

Mike,
I spent some time checking out the wiring of the wiper switch and motor and found the following.
Blue/Light Green is actually High speed and Red/Light Green is Low Speed. The wipers work fine now. I also did away with the column switch and wired everything to toggle switches (the original switch was beyond repair (may purchase a new one later). That left me with the Brown/Light Green wire for "Park" Never could get that to work (I made a connection between a green hot and the Brown/Light Green - is that correct?

Thanks!
Eddie Haynes

After studying the Link again, I realized the Brown/Light Green connects to the Red/Light Green Low speed switch to activate the parking function when wipers are turned off.
All should be in order now.
Thanks again for the link...
Eddie
Eddie Haynes

As you say, with the manual switch off brown/light green (park) is connected to red/light-green (slow). With the wipers not parked the park switch extends 12v on the brown/light green and hence to the slow speed winding of the motor to keep it running. When the wipers reach the parked position the park switch changes over from outputting 12v to outputting earth on the brown/light-green, and hence the slow speed winding. This has the effect of stopping the motor pretty-well instantly.

When power is simply disconnected from a motor, as in the previous arrangement, the motor only spins down relatively slowly, which can give an erratic parking position depending on how wet the screen is. But when a motor *is* spinning down, it is acting as a dynamo i.e. generating a voltage. In the later park system with earth both sides of the slow-speed winding from the park switch having changed over, and the motor still running, that's effectively a short-circuit on a dynamo output. It tries to generate a high current, which makes it much harder for it to turn (for the same reason your idle slows when you have maximum electrical loads switched on) which stops it very rapidly. This gives it a much more consistent stopping position.
Paul Hunt

This thread was discussed between 26/10/2014 and 28/10/2014

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now