Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Later Classics wipers explained

Have been unable to find any in depth explanation of the functioning on the wiper control system used on recent Morgan Classics with wash and delayed wipe, or indeed of similar on any other marque. Below is my attempt at explaining the system based on research into chassis loom, delay relay and wiper stalk. Models at least back until 2006 and onwards to end of Classic production, appear to employ both the same wiper stalk and delay relay so should function similarly. Note it functions standalone with no connection whatsoever to CANBUS, ECU or BCU.

The Lucas 14W two speed wiper motor has the usual self parking mechanism employing an integral changeover switch operated by a cam on the drive wheel. This allows continued current to motor after wipers are turned off until the cam, coinciding with the wiper park position, throws the switch to ground the normally live side of the motor. This puts a short on the motor windings and with help from the motors back emf brakes it, so preventing overrun of park position. The motor has three brushes oriented to allow slow and fast wipe speeds. Wipers are controlled by the right hand Lucas steering stalk.

A downward pull on the stalk against spring detent engages slow wipe, allowing a single wipe with timely release. Pulling stalk forwards against spring operates screen washer pump whilst simultaneously applying +12 volts to a timed hold trigger on an IC within a dedicated six pin wash/delay relay. The IC then conducts on the ground side of the relay coil. As the other side of coil is permanently connected to +12 volts whilst ignition on, this allows it to energise and switch the changeover contacts to allow current to slow speed connection on wiper motor. The coil remains energised by the IC long enough to allow three further slow wipes after stalk is released.

First twist position on end of stalk engages delayed wipers commencing with a single slow wipe. Each of five delay periods are selected by an inner knurled twist selector, longer downwards. Each position switches a resistance array within the stalk in the range zero to 7.5KΩ (max delay) and fed via a flying lead connector to a circuit providing a varying voltage to a second delay trigger on the relay IC. After delay the coil is energised briefly to allow another single wipe before repeating.

Further twists on end of stalk engage slow then fast continuous wipes independant of delay relay. Note in each case after relay coil is de-energised by IC or wipers de-selected, the self parking mechanism takes over such that the briefest of wiper commands will produce a full wipe.

Note the wiper delay relay has a sixth pin labelled "I" and narrower than the others. It appears MMC use a modified 5 pin plug-in base which may not provide an adequate captive connection for same so worth checking.

Replacement part numbers:
Motor: Lucas 14W 12v 2 speed PARK->
Stalk: Lucas STC4016 or SQB161
Delay relay: Wehrle 60 201 002

A very impressive bit of investigation and explanation of the control system for the wipers Richard...

Well done, thank you for the explanation.
Bob.

Thanks for that. Useful info.

For a Morgan that's surprising complex, thanks for the explanation Richard

Mine only turns off when it feels like it sometimes continuing for several minutes.

Thanks for kind comments. I think the wiper functionality is the bare minimum nowadays though Jon. Good news is that all the clever stuff is provided by the delay/wash relay, a simple plug-in replacement. There are other 6 pin wiper relays available with same pin-outs including the one used by Land Rover in conjunction with same stalk as here, so that may be a useful alternative to Wehrle one.

Our F54 Mini goes one step further in functionality. The similar stalk delay switch controls screen mounted rain sensor sensitivity instead of fixed delays. This allows auto chosen delays as needed, even (rather annoyingly) auto switching to high speed if the rain on screen gets too heavy.

Great bit of digging here Richard. Finally demystified the workings of the wipers for me! Thanks.

Richard - do I have your pomission to use your article in the next Thames Valley Newsletter?

PM sent Steve.