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Firstly, Merry Xmas and holiday greetings to you all from Japan.

I've been fitting an Amazon aftermarket starter solenoid to my '97 900SS today and it comes with extension wiring and connector (no more original white connector shaking loose) So far, so good. But when I started removing the insulation on the old frame side connector, I found this diode. Is it standard? If so, I'll refit into the new connector. If not, what's it doing there?
 

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The diode prevents a reverse current spike from the solenoid when it switches off and the field collapses.

It's not required but is protective in purpose.
 

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The diode is better to have in than out.

Here's a couple of threads from a while back on the topic... The first one has a post from me as to why you should have the diode - and what it does (prevents back EMF from the coil of the solenoid relay). Part of my learning process on this forum. ;)

http://www.ducati.ms/forums/57-supersport/325713-starter-relay-coil-connections.html

http://www.ducati.ms/forums/57-supersport/422986-diode-replacement.html
Steve, many thanks for that, today in fitting a new connector to match the new solenoid, I buggered up the old diode in failing to remove it from the old connector, so proceeded without. Bike started up as if on steroids, couldn't be happier. Then I read your above links and although Punch, whose opinion I totally respect says do without, I'll err on the side of caution, and will now source an appropriate IN4004 diode and refit.
 

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Steve, many thanks for that, today in fitting a new connector to match the new solenoid, I buggered up the old diode in failing to remove it from the old connector, so proceeded without. Bike started up as if on steroids, couldn't be happier. Then I read your above links and although Punch, whose opinion I totally respect says do without, I'll err on the side of caution, and will now source an appropriate IN4004 diode and refit.
Yeah, Punch is a smart cookie - even if he is an Aussie... ;) IN4004 or a IN4007 should be OK if you can't get a IN4004. When I fitted my new solenoid, I just hooked into the original wiring, and left the OEM plug with diode in place. It's all worked fine so far (3-4 years). I didn't want to remove the OEM plug, just in case I ended up fitting a OEM solenoid at some time in the future.

At least with fitting the diode, you can't go wrong - while not fitting it, leaves you open to possible problems in the future.
 

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Steve, many thanks for that, today in fitting a new connector to match the new solenoid, I buggered up the old diode in failing to remove it from the old connector, so proceeded without. Bike started up as if on steroids, couldn't be happier. Then I read your above links and although Punch, whose opinion I totally respect says do without, I'll err on the side of caution, and will now source an appropriate IN4004 diode and refit.
I don't remember writing "do without" but maybe that was some time in the past after a few drinks!

I would certainly not "do without" on an EFI (ECU) controlled bike as the seriously negative (reverse polarity) voltage pulse could blow the crap out of the ECU

Please post the link to thread where you found that and i will post a correction in case someone in the future reads it.

From other posts/threads it does appear that the 5X ECUs might not have reverse polarity protection as those posts indicate that reversing the battery unintentionally can blow an internal PCB track. Makes me think there is not a diode inside the ECU to protect it from this cockup.
 

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I don't remember writing "do without" but maybe that was some time in the past after a few drinks!

I would certainly not "do without" on an EFI (ECU) controlled bike as the seriously negative (reverse polarity) voltage pulse could blow the crap out of the ECU

Please post the link to thread where you found that and i will post a correction in case someone in the future reads it.

From other posts/threads it does appear that the 5X ECUs might not have reverse polarity protection as those posts indicate that reversing the battery unintentionally can blow an internal PCB track. Makes me think there is not a diode inside the ECU to protect it from this cockup.
Hi Punch - it was this post: http://www.ducati.ms/forums/57-supersport/325713-starter-relay-coil-connections.html#post3262801 - and another one in the same thread (a bit further down) where you said it. But that was when we were all figuring out what exactly it did, and why. :) Then we worked out the why of "why is it there at all?", and things changed to 'replace it!'. ;)
 

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Hi Punch - it was this post: http://www.ducati.ms/forums/57-supersport/325713-starter-relay-coil-connections.html#post3262801 - and another one in the same thread (a bit further down) where you said it. But that was when we were all figuring out what exactly it did, and why. :) Then we worked out the why of "why is it there at all?", and things changed to 'replace it!'. ;)
Guilty !!

Can't explain as I have known about diodes across coils for years.
Maybe, just maybe, it was on the assumption that ECUs would have a a diode in the power supply rail to provide reverse polarity protection.

For the sake of a few cents, they certainly should be fitted to the starter solenoid.
 
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