flat battery maybe

Sounds like fuse 1 is corroded....... or ignition swith needs a good clean

Experienced the same issue just recently on " Red"     cleaning ignition switch was the fix 

Quite a few posts on this proceedure in the forum

Good luck

is it a 2 valve or 4 valve K100RS?

When you turn the key on, you should hear a faint click from the relay box, that's the load shed relay closing as it gets power from the ignition switch to pin 86. If it loses power when the brakes are applied, clean the ignition switch. If it doesn't lose power, the problem could be at fuse one or the kill switch. A test for this would be a temporary jumper wire to bypass the kill switch. Or if there's power going into the kill switch, but no power coming out, with the button pressed (which supplies fuse one) it's the kill switch. In other words, is fuse one supplied with power when the ignition is on, and also when the start button is pressed?

Give the fuse holders a spray with electrical contact cleaner, and replace the fuses with new ones, even if they have continuity. Check that they are tight, and that the  wires have full, clean contact to the relay holder. The fuses are deliberately the weakest link, and deliberately the easiest thing to do.

It will help if you tell us if it is 2v or 4 v. For 1990 it could be either and they are different.

Has it ABS?

Thanks for all the suggestions!

It is a 4V without ABS. Seems I could start by checking the ignition switch based on your replies. I am also planning to check the light bulb monitor.

Will post an update once I have had the chance to try these!

Cavaliere ordinario wrote:Grazie per tutti i suggerimenti!

È un 4V senza ABS. Sembra che potrei iniziare controllando l'interruttore di accensione in base alle tue risposte. Sto anche pensando di controllare il monitor della lampadina.

Pubblicherò un aggiornamento una volta che avrò avuto la possibilità di provarli!

Ho la stessa moto tua, ho avuto lo stesso problema lo scorso anno e l'ho risolto con la sostituzione del blocchetto di accensione posto sotto alla chiave di avviamento.
Un saluto.

Cannot remember if Finnish people speak or read Italian.....

The 4V bikes have a switch on the centerstand, wich sometimes cause trouble.
Unplug it (connector in right triangle) and "shortcircuit" it, bike should start.

Arlina wrote:Cannot remember if Finnish people speak or read Italian.....

The 4V bikes have a switch on the centerstand, wich sometimes cause trouble.
Unplug it (connector in right triangle) and "shortcircuit" it, bike should start.

... but what are translators for!!

Mon aéroglisseur est plein d'anguilles.

Laitch wrote:Mon aéroglisseur est plein d'anguilles.