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Have a new (to me) 1975 R90/6. Was starting fine until I fixed the indicator lights. They now work fine, whereas before left hand signals previously would flash but then stay lit.

Now, bike will not start when I press the rhs start switch. No click of starter, nothing. New starter relay and voltage regulator, new battery cables, battery testing over 12v. Starter relay red wires light both sides with test light. Headlights: low beam fine, high beam fine, park works.

If I connect my test light to negative and touch it on brown wire on rhs starter switch, bike fires right up.

What do you think? My next guesses ground somewhere, lhs switch faulty, or maybe diode behind connector board shorted, or something connected to light relay. Any help greatly appreciated, really got me puzzled. Thanks all.

Winstonfly wrote: ↑Fri Jun 10, 2022 4:30 am If I connect my test light to negative and touch it on brown wire on rhs starter switch, bike fires right up.

Welcum.

As usual....Simple to troubleshoot in person, harder when done remotely...
Test the neutral light switch and clutch switch and their circuits.
Current should only flow one way through that diode on the board.
Should be an easy fix.
This diagram might help.

https://www.r90s.info/Articles/R90S+Wiring+Diagram.pdf

OK, I assume that... when you say "If I connect my test light to negative and touch it on brown wire on rhs starter switch, bike fires right up" you mean that you short the brown on the starter button to ground AND press the button, the bike turns over...

If this is true, the issue is almost certainly in the circuits that earth the ground side of the starter button. This is the matrix of switches and diodes that provides a ground when the bike is either in neutral or the clutch is pulled (or both). Some questions...

1) Have you tried starting the bike with the clutch pulled?

2) Does the neutral lamp on the dashboard work correcly?

With the answers to these questions, it should be possible to say where the problem is.

I am attaching a functional wiring diagram for the Starter/Clutch/Gearbox interlock wiring which may help with the problem. There is one inaccuracy... the label Green/Black at the top should read Green/Blue.

Let me know the answers.

Rob

Rob Frankham wrote: ↑Fri Jun 10, 2022 12:30 pm This is the matrix of switches and diodes that provides a ground when the bike is either in neutral or the clutch is pulled (or both).

You used 'diodes' in the plural form. Is there more than one for this circuit?

Rob Frankham wrote: ↑Fri Jun 10, 2022 12:30 pm I am attaching a functional wiring diagram for the Starter/Clutch/Gearbox interlock wiring.....

Looks like it didn't 'attach' ????

If everything was working OK before messing with the flashers, this wire probably was probably accidentally disconnected.
That would explain it.

Thanks very much GSPD and Rob. Answering those questions:

I’ve tried starting bike with clutch pulled in, in neutral and in gear. Nothing.

The neutral light operates correctly. Looked for abnormal illumination whilst doing all this and operates normally.

My understanding as per wiring diagram is that in more immediate circuit in question there is a single diode behind the connector block lhs of connector in 85b LKK proximity. I did try testing this with a multimeter yesterday, not sure I did it right, but checked both directions by switching red and black and got zero readings either direction.

Did you check the blue/white wire I pointed out in my previous post?

The diode doesn't affect starting; it's s only there so the neutral light doesn't go 'on' every time you pull in the clutch.
If the diode fails (open circuit) the bike will only start with the clutch pulled in regardless of if it's in gear or in neutral.

I don't think that type of diode can have a 'short circuit' type failure. Rob F, what say you?

Based on your initial post...
Temporarily by-pass the safety interlock circuit(s) by running a jumper wire from your battery negative to your starter switch blue/white wire; the bike should start when you press the start button, wether it's in neutral or in gear, wether clutch lever is in or out.
If it doesn't, your actual starter switch contacts are faulty but I really doubt that because you said everything worked before fixing the flashers.

Thanks GSPD, that worked. Not a permanent fix, but I guess it confirms quite a few things.Starter and solenoid must be fine etc.

The blue/white wire from your starter switch to the board is broken/disconnected...or the board is cracked (very unlikely).
You need to restore continuity from that blue/white wire at the switch and BOTH blue/white wires at the board (red arrow and the wire right below it).
That will restore everything back to norbal.
If you're unsure, post a clear pic of your circuit board, I can pinpoint exactly what you have to do. p.s. Please call me gspd, GSPD is my bike.

OK, so here is the diagram... I've corrected the wire colours...

If you can answer the questions in my previous post, it shouold be possible to pinpoint the source of the problem.

Rob

Thanks very much to both of you. I’ll post some photos in the morning that might help. Rob, I posted answers above but let me know if there were others I missed. I noticed today the previous owner had removed clutch switch on lhs. Also checking out that wire in particular gspd . Thank you