Help with wipers not shutting off

[Leester]

First off thanks to everyone on this site for indispensable help getting my 1970 280SL back on the road after a long restoration process. Second, I have read and re-read, and re-re-read every post and material in the tech manual regarding the ww wiper function.

As stated in the subject line, wipers do not turn off.

I suspect that my multi-function swith is not working properly and plan to send off to Sead but once I do that, I can't do any more diagnosis until it comes back.

Working today I discovered, by accident, something that seems strange. I have been unplugging and plugging in the connector for the multi-function switch under the dash. I didn't realize it was unplugged and when I turned on the ignition switch I got 12 volts at the wiper motor at both in 4 and pin 1. We know that pin 4 is supposed to get 12V straight from fuse 2 so that makes sense. But how did it get 12 volts at motor pin 1 with the mult-function switch unplugged?

Then I unplugged the connctor at the WW relay and now get 12v only at motor pin 4.   I thought the wiper motor was turned on and off with the multi-function switch.

As an aside, the park feature of the wiper motor works correctly.

If the WW relay connector is plugged in to the relay, it looks like there is 12v at relay pin 56b. In order to get 12v to wiper motor pin 1, I'm guessing that it is gettting that 12v from 56b on the relay to pin 56 on the relay. But if this is correct, it seems like the motor will always run.

So, how is current supposed to be shut off to pin 56 at the relay?  And is this even the right question?

If the multi-function switch connector is connected under the dash, it does pretty much the same thing and pushing on the switch does nothing, which is why I suspected the multi-function switch. But if it performs the same way with the multi-function switch disconnected, then it seems as though it may not be the switch.

I have checked and rechecked the wiring colors and am as sure as I can be that they are correct and I can provide them if that helps.

Thanks in advance for any insight into this.

[BobH]

Hello Lee, the wiper relay is a latching relay, it switches on with a pulse from the stalk switch, and stays on until it gets a second pulse to turn it off.  If the relay is "on", then you will get a +ve supply at pin 1 on the motor, even with the stalk switch disconnected

If the stalk switch isn't working properly, then the relay may not get the reset pulse to turn off.  There's a write up in the manual about how to repair a faulty wiper switch

If the stalk switch seems ok, then I would check the relay, make sure it's switching off when you operate the stalk switch again to reset the relay, perhaps it's sticking in the on position.

If the relay checks out OK, i'm not sure if it might be the internal contacts of the motor, but i'm not sure how these would prevent the motor from stopping though

Please report back

[Leester]

Thanks Bob,  I should have included that the relay I'm using is new from Auth Classics. I do understand that even new parts may not work correctly - have seen that movie. So perhaps next question is how to bench test the relay. And is there a way to replicate the pulse that the relay would normally get from the switch?

I've done a lot on this car myself and I'm not shy about taking things apart but once in a while I'm willing to have an expert with experience handle things.   

[BobH]

Hello Lee, with everything connected, just dab a +ve supply (probably best from fuse *2 or link across from terminal 4 on the motor if easier) onto terminal 86, the motor should either stop, or start, apply it a second time and the motor should start or stop

If that works, but the relay isn't getting the signal from the switch, it's either a bad switch, have a look in the tech manual for a repair, or perhaps a poor connection somewhere between the switch, connector or relay

[Leester]

Thanks Bob, tried that; works like a charm. Wiper motor turned off and parked.

Thank you SO MUCH.

This site and its members are awesome.