"Bouncing" coil on an intermittent wiper relay - Defender Source
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  #1  
Old December 12th, 2017, 09:40 PM
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Eric Wages
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"Bouncing" coil on an intermittent wiper relay

Hi folks, soliciting input to check my debugging process.

I'm in the process of adding intermittent wipers to my '88 110. I've bought the intermittent wiper arm, harness, and programmable relay, and got it all wired up. The problem I'm experiencing is that, when in the intermittent wiper setting, the coil "bounces" and rapidly toggles the pass-through input; it's not staying energized, nor having clean on/off function.

It *does* sometimes stay energized and work properly, but it's maybe 1 out or 4 wipes. When it bounces, it'll reset the timing, or wipe continuously and then reset. I was thinking that maybe the new arm had some schmoo in it, but I checked it all out and it looks good. Ground looks good. I was thinking that the problem is either the parking switch or the new wiper switch.

I'm thinking that the new switch may be culprit as the wipers will park no problem when using any of the two normal settings.

Debugging thoughts? Any guesses on how best to debug before I start throwing more parts at it?
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  #2  
Old December 12th, 2017, 10:22 PM
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John B.
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Sounds like a bad relay. I would first try a stock, non-adjustable relay. Everything else in the circuit is dead simple stuff, so unlikely to cause an issue like that.

This is assuming you have done everything as per a stock 200TDI+ truck's wiring.
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  #3  
Old December 12th, 2017, 10:33 PM
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Eric Wages
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I haven't modified the wiper setup in any way from my original 19J config barring buying the proper timer harness and wiper arm, timer relay, and plugging the assembly into the old harness port and grounding out the relay.

I don't have a non-timer relay, but I'll probably source one and do some more debugging. The relay I've got is a new Bosch unit, so it's not a blue box special.
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  #4  
Old December 16th, 2017, 11:37 PM
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Eric Wages
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Swapped with a unit I got off of amazon. Still "bounces" a little bit from what I hear, likely due to the park switch electrically bouncing. But it's solidly working now, just not adjustable
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Old December 17th, 2017, 03:24 AM
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IME, "bouncing" of a relay at audible frequencies (like rapid clicking) usually results because of a poor electrical connection between ground, Vcc, or the coil energizing terminal. Usually actual switch bounce is at a frequency way beyond what a human could discern.

I think your circuit debugging technique is a good one. It should be easy to shunt the remaining switches in your circuit (the parking switch and wiper switch) to isolate the issue.

Is it possible that the wiper or something uses an varying resistance to act as a primitive method of closed-loop feedback? If so, is it possible that such a varying resistance is driving a voltage divider used to feed the relay? If so, is it possible that a voltage held between +12V and ground could cause a floating condition in the relay?
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