UK Monster Owners Club Forum » .: Technical :. » Electrics » S4 Lighting relay where is it ???

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Old 10-08-2019, 12:14 AM   #31
Flip
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Yes I can see that- just looking through the schematic of my 1997 900 and it's there across the solenoid terminals and I can see why it could be on the blue wire (assuming it is the same of course but we all know what assumption is) from the light switch as that is directly from the 7.5A fuse D4 (turn signals, side, tail and warning lights) and then there is a return wire from the light switch back to the ignition switch where the side light circuit (with ignition on) picks up from the Parking light circuit (steering lock on).

But crucially there is the wiring from the ignition switch through to the General Relay, Fuses, Battery and Starter Solenoid (and obviously going to the Starter and Kill switches) which is all live with the ignition on thus the reason for the diode to protect it all.

You can also see from the schematic why (although it seems to vary bike to bike) that the General relay arcs so badly (speeding up its' demise) from the charge in the coils when you switch the motor off using the key.

Whereas using the kill switch to stop the motor running prevents this while the switch contacts remain unaffected.

If you're intrigued by that, prise the yellow cover off the relay and see if the contacts spark over when you turn the motor off with the key, then try it again using the kill switch.
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Old 10-08-2019, 09:56 AM   #32
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Originally Posted by Luddite View Post
Have a look at the thread Lucaz started on the Ducati Forum, particularly the picture in post #3.

https://www.ducatiforum.co.uk/thread...this-for.4933/

It's a diode to stop a voltage spike travelling back down the loom when the starter solenoid disengages. Does your bike have one in the same place? If not, I'm wondering if yours was moved, as some posts suggest Ducati relocated it further up the loom to protect it from damage.
Thank you .... that now makes much more sense and I'm wondering whether it was a retrofit/modification done at the dealers rather than the factory .... judging by the state of the soldering ?


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Originally Posted by Flip View Post
Yes I can see that- just looking through the schematic of my 1997 900 and it's there across the solenoid terminals and I can see why it could be on the blue wire (assuming it is the same of course but we all know what assumption is) from the light switch as that is directly from the 7.5A fuse D4 (turn signals, side, tail and warning lights) and then there is a return wire from the light switch back to the ignition switch where the side light circuit (with ignition on) picks up from the Parking light circuit (steering lock on).

But crucially there is the wiring from the ignition switch through to the General Relay, Fuses, Battery and Starter Solenoid (and obviously going to the Starter and Kill switches) which is all live with the ignition on thus the reason for the diode to protect it all.

You can also see from the schematic why (although it seems to vary bike to bike) that the General relay arcs so badly (speeding up its' demise) from the charge in the coils when you switch the motor off using the key.

Whereas using the kill switch to stop the motor running prevents this while the switch contacts remain unaffected.

If you're intrigued by that, prise the yellow cover off the relay and see if the contacts spark over when you turn the motor off with the key, then try it again using the kill switch.
That's interesting .... so from now on I should shut her down with the kill switch ?

and probably best to put another diode back into the same place and same orientation?

The text stamp on mine reads "6A05" which seems to correspond to diodes I've found on ebay for about £4 for x5
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Old 10-08-2019, 10:08 AM   #33
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Hi, from the Handbook, " Warning- this switch is mainly intended for use in emergencies when you need to stop the engine quickly"
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Old 10-08-2019, 10:39 AM   #34
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Originally Posted by LVC View Post
Thank you .... that now makes much more sense and I'm wondering whether it was a retrofit/modification done at the dealers rather than the factory .... judging by the state of the soldering ?




That's interesting .... so from now on I should shut her down with the kill switch ?

and probably best to put another diode back into the same place and same orientation?

The text stamp on mine reads "6A05" which seems to correspond to diodes I've found on ebay for about £4 for x5
Personally I would try and prise the yellow cover off the General Relay to have a look at what goes on before worrying about it- it certainly doesn’t seem to affect all bikes. I only found it because soon after buying my bike it seemed to eat relays. A couple of ‘bleed resistors’ can solve the issue but that’s a whole ‘nother thing.

But yes I would definitely look at getting the diode back in the circuit somewhere- they are cheap enough but if you have trouble let me know- we’ve probably got some at work. In addition I would use some heat shrink sleeve over it to give it a little more protection.

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Originally Posted by gemantsdad View Post
Hi, from the Handbook, " Warning- this switch is mainly intended for use in emergencies when you need to stop the engine quickly"
Yeah that’s simply because in an ‘emergency’ your fingers are a lot closer to the kill switch than they are fumbling around with the ignition key.

The ignition switch is simply a way of making turning it on and off secure so only the owner (in an ideal World) can operate it- many old classic bikes (along with competition machines) don’t have keys.
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Last edited by Flip; 10-08-2019 at 10:42 AM..
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Old 10-08-2019, 01:36 PM   #35
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But yes I would definitely look at getting the diode back in the circuit somewhere- they are cheap enough but if you have trouble let me know- we’ve probably got some at work. In addition I would use some heat shrink sleeve over it to give it a little more protection.
Thx, would this one work ?

ebay item number : 113688671255
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Old 10-08-2019, 04:04 PM   #36
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To be honest I’m a little confused as to why they used a 6amp rated diode when, if the blue wire on your bike is the same as mine and on a 7.5amp circuit. Or if like you thought, is the wire for the headlight and therefore on a 15amp circuit making it an even worse choice.

It is still worth finding out which fuse that wire actually goes to just for future knowledge but I think I would be looking at a higher rated diode such as this:

https://rover.ebay.com/rover/0/0/0?m...2F192608781257

These are basically the same kind of ‘blocking’ diode used on those little battery charging solar panels to prevent the battery sending voltage to the panel instead of the other way round.
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Old 10-08-2019, 04:24 PM   #37
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Originally Posted by Flip View Post
To be honest I’m a little confused as to why they used a 6amp rated diode when, if the blue wire on your bike is the same as mine and on a 7.5amp circuit. Or if like you thought, is the wire for the headlight and therefore on a 15amp circuit making it an even worse choice.

It is still worth finding out which fuse that wire actually goes to just for future knowledge but I think I would be looking at a higher rated diode such as this:

https://rover.ebay.com/rover/0/0/0?m...2F192608781257

These are basically the same kind of ‘blocking’ diode used on those little battery charging solar panels to prevent the battery sending voltage to the panel instead of the other way round.
It's on the 15A fuse marked as "Tail Light + Turns + Pilot Light" - 3rd up from the bottom on the box. The 7.5A one above it is for "Passing".

Your choice makes more sense to me, thx
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Old 10-08-2019, 04:50 PM   #38
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It would be interesting to see what the actual current draw on the blue wire is. After cutting the wire but before attaching the diode, you could put a multimeter set to amperes between the two ends and see what it reads with the indicators, pilot and tail lights on.
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Old 10-08-2019, 06:23 PM   #39
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It's on the 15A fuse marked as "Tail Light + Turns + Pilot Light" - 3rd up from the bottom on the box. The 7.5A one above it is for "Passing".

Your choice makes more sense to me, thx
I’m still not convinced the turn signal circuit should be on a lower current circuit than the headlight.

I checked on my YZF600R and the turn signals etc. including the fuel pump is on a 15amp fuse whereas the headlight is on a 20amp but the pattern is the same as my Monster.




Perhaps someone else with an S4 could have a look at their fuse box to confirm or deny my theory?

Quote:
Originally Posted by Luddite View Post
It would be interesting to see what the actual current draw on the blue wire is. After cutting the wire but before attaching the diode, you could put a multimeter set to amperes between the two ends and see what it reads with the indicators, pilot and tail lights on.
Yes I agree and I am sure it is pretty conservative but it wouldn’t be the first time Ducati have used rather marginal wiring on their motorcycles but either way I still don’t understand why a lower current rated diode would be used as if it’s having to work (which presumably it is) it’s only going to keep getting hot and eventually fail as this one did.

Excess heat on the rectification (diode) side is exactly why we get failures in the shunt type regulator/rectifiers.
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Old 10-08-2019, 06:46 PM   #40
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Perhaps someone else with an S4 could have a look at their fuse box to confirm or deny my theory?
Now, we all know that Ducati owner's manuals can't always be taken as gospel but this is what the 2001 S4 one shows...





The blue wire goes into the fuse box at number 14 and the 6-14 fuse should be 15 amps.
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Old 10-08-2019, 09:18 PM   #41
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Yes indeedy ....



Thanks @Flip for explaining why it burnt out .... makes sense if it is only 6A

and many thanks to both of you for taking the time to help - glad to see the willingness to assist is still alive after all the years

I will order one of the diodes suggested at the correct rating and add it back into the circuit where the old one was and then I may even change the insurance to road use (rather than storage) and actually take her for a spin or two
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Old 11-08-2019, 09:22 AM   #42
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Originally Posted by Luddite View Post
Now, we all know that Ducati owner's manuals can't always be taken as gospel but this is what the 2001 S4 one shows...





The blue wire goes into the fuse box at number 14 and the 6-14 fuse should be 15 amps.
Yes very true- thanks for posting that up.
It would interesting to know whether the headlight is on the 20amp circuit of the injectors and coils etc. thus following the same pattern at least.

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Yes indeedy ....



Thanks @Flip for explaining why it burnt out .... makes sense if it is only 6A

and many thanks to both of you for taking the time to help - glad to see the willingness to assist is still alive after all the years

I will order one of the diodes suggested at the correct rating and add it back into the circuit where the old one was and then I may even change the insurance to road use (rather than storage) and actually take her for a spin or two
Glad we helped a bit, it’s always difficult trying to diagnose without actually being able to trace the wires etc. and even harder without a diagram to follow.

Now get it sorted and enjoy it on those lovely French roads around there.
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Old 03-09-2019, 08:02 PM   #43
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Righto chaps .... postie delivered the new Diode today (and his 9 brothers .... for £0.90 for 10 what could I do ^^) so tomorrow is soldering day .... it's not going to be neat but hopefully it'll function and I'll hide it all under heat shrink once we're good

Look out Frenchie roads the beast is back
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Old 04-09-2019, 08:08 PM   #44
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Thumbs up

Well it wasn't far and it wasn't fast but for the first outing she's had in over 4 years ..... god it felt good







Thanks all for your help
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Old 04-09-2019, 08:40 PM   #45
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Glad you got it sorted and good to see it up and running in the lovely looking French Sunshine.
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