APRILIA RS 125 : Aprilia RS 125 motorcycle motorbike starter motor circuit testing ( will not turn over , no crank issue )

Aprilia RS125 workshop manual for sale Ebay UK

Ok so its quite simple and robust but it can be problematic at times to narrow down any faults with the starter system .

here is a wiring diagram of all wiring side components .

Aprilia RS 125 motorcycle motorbike starter motor circuit testing ( will not turn over , no crank issue )

so on the electrical side you have ( click on each to see tests posts all will be done within next week )

battery , key- ignition switch , start button , kill switch , stand switch , starter relay , starter motor .

mechanical

Bendix , bendix cover , starter ring ( flywheel ) .

So if i came to a bike that would not start or turn over No crank issue .

firstly id charge the battery or use my jump starter kit , watch this video to see how the starter bendix fails to
engage when the battery is not charged enough .

Next try to start does it click or try to turn but stop or clunk this can give you a good idea of problem but for this post ill just go step by step according to our list above .

Low amp side ( control side )

the low amp or control side is used via relay so that you can control and major or high amp circuit with a small switch or push button at the handlebars , the low amp control circuit close the contacts of the relay to
operate or touch the 2 large starter motor circuit wires together .

I would jump straight to starter relay turn key on and test at relay for 12v to earth on one of the small connectors ( yellow/red) if you get positive here this verifies the Key - Starter button - test the other small connector now ( green / yellow ) this should have continuity to earth .

here i show tests with my 12v light tester

First plug the connector end to negative on battery and the other probe end into the Yellow / red wire one of the small wires going to starter relay ( key / starter button side ) .

when you press button the test light should light up to show a good path through the key to the starter button and then onto the starter relay .

connect scope on a rope (test light ) connector to negative terminal

connect probe end of test light to yellow and red wire

( 1 of small connector at relay )

operate button and it should light .

This tells me that the Key and the starter button work if it did not light i would check fuses although this would of been first on the list , test key and starter button and then look at any connectors in between the key and starter relay .

Next i connected to positive terminal of battery as this side of relay should be going to earth .

and at first it did not light i moved the stand up and down and nothing

so i disconnected the stand switch and eventually got it to light up .

( So my problem here was stand switch not earthed the

low amp circuit side of starter relay )

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( though it was simple now half way through 2 hours in and i am still rambling on )

High amp direct battery to starter motor side

OK so looking at the wiring schematic for the starter system the 12v high amp starter motor circuit goes from

an earth battery down via the positive ( red ) high amp wire to one of the large relay posts ( red wires )

One of these larger red wire should be permanently live so connect test light ( scope on a rope ) to the negative terminal of the battery and test both wires at relay the one that lights up is the permanent live feed direct from battery if non light up you have wiring problems from battery to relay post ( or an earth problem )

Now set your test light on the opposite side cable - large post red cable this is the wire going direct to

the starter motor , press the starter relay button and you test lamp should light up meaning that relay is in fact

working and closing the internal high amp contacts , it might be good to read this post of testing relays

now so you understand how it should operate .

Now if the test light lights you can move on to the starter motor now , if it does not light then

we know the control circuit is ok so it must be relay failure ( replace this and move on to starter motor )

Testing at starter motor , so we now know that the control side of relay is ok and the high amp direct

power supply to the relay is ok and that its passing through the relay ok too .

So testing at the starter motor now begins , test for 12v at starter motor terminal with button pressed for starter operation if not 12v is found then check wiring from starter relay too the starter motor and dismantle the starter connection and rebuild cleaning it .

If you do have 12v here its time to do a volt drop test watch this excellent video to understand voltage drop and how its important regards starter motor testing