Modern Vespa

Hi there, I've got a strange problem. Bought a scooter in an auction. ECU/MIU/Throttle body was missing and ignition lock damaged. I bought and fitted new ECU+lock set, coded ECU to brown key and bike starts.
But it starts when applying one of the brake levers- not the start button. First I thought its something simple, but after checking all things it doesn't look like it. I checked brake switches, kill switch, start button, starter relay. They all work as it should. All the wiring looks new-it doesn't look like somone has tampered with it
Also I've downloaded workshop manual for 2008 GTS 300 Super- should be similar. There is a section with a simplified starting circuit diagram- looks simple: power is going through the ignition switch to fuse to either brake switch and through start switch to starter relay to ECU. Yes, one of the starter relay wires going to ECU unlike older bikes. I measured voltages between switches and components with ignition off, ignition on and when brake applied and I get strange readings:
1.There is continuity between brake switch and start button. But with ignition on 12V on start button and no Voltage on brake switch. With ignition on there is 5V to other side of the start button wire.
2.There is continuity between one of the wires from start button to starter relay with ignition on and not pressing starter button.
3.Also when i start the bike there is no voltage present on one side of the starter relay

So to sum up : I am completely confused- can someone steer me to the right direction. Thanks!

Check which sides of the switches and relay you are measuring by using the wiring colours shown in the wiring diagram.

http://manuals.wotmeworry.org.uk/Vespa/GTS300%20Super/

The wiring may have been messed with by whoever removed/tampered with the ECU and ignition switch.

Initial thought is the relay which switches power to start switch when the brake is applied is wired wrong try switching the feed wires around,
I think what should happen (but I will stand corrected) is;
You should have no power to the start switch without the brake lever applied, when the brake lever is applied this will also throw the relay on the same circuit and feed power to the start switch, which in turn will also throw power to the starter motor, this way when the scooter has started and you press the start button in whilst running (without the brake applied) the starter switch will not throw power to the starter motor and try to mesh,
If this is correct it will also enable the settings which can be altered with the start switch to be accessed whilst running and not throw the starter motor into mesh whilst doing so.
I hope this helps but please if you find the solution please share with us cause we might need the info one day

Thanks jimc for the wiring link- will be very useful. Just can't understand why 3 wiring diagrams on that pdf- they look the same.
And thanks dieseldog for explanation- thats how it should work I think!

I will check with a wiring diagram and will report back!

Looked at the wiring diagram and did some further testing, but something is totaly not right there.
Up to the brake switches all seems good: power comes with ignition on, when you press the brake power goes further, but it's not reaching start button.
Instead there is power on outgoing pin on start button after I swich ignition on, but no power to incoming starter relay pin! But when i apply brake there is a power to incoming starter relay pin (bike starts). Somehow seems like start button is removed out of the loop.
I am thinking maybe it's something to do with a ECU? Because another thing I've noticed that after I start the bike (with a brake) and bike is running and i press the brake -starter motor is not spinning anymore. So I am thinking that's not just a simple splice-and-bypass of the start button.
I am considering making new mini-loom (rear brake light, brake switches, start button, starter relay) to cut the unknown, but it's a big one...
Lost...

Dieseldog- about what relay you are talking? In the simplified wiring diagram there is no start relay as such like on some other bikes. I know there are 3 relays at the front: fuel pump relay, headlight relay and I think fan relay. Please correct me if I am wrong. Thanks

Note that the ECU provides the 'ground' of the relay's coil. This can measure any sort of voltage with a high impedance meter (the average multimeter) when the ECU wants to inhibit starting, and is only pulled to ground when the ECU is happy for the starter to be actuated. So this circuit is disabled when the immobiliser is active, and also when the engine is running and 'happy' (headlight comes on).

Chase the wire between the brake switches and the starter button - white/black IIRC.

Chase the wire between the brake switches and the starter button - white/black IIRC.

This would be the logical thing to do,

I just posted my initial thoughts when I said about the starter relay, I will have a ganders at the wiring diagrams and see what I can make of them, ( I hadn't looked before posting, sorry if it's caused you more problems).

Does the starter button have to be pressed in and kept in when starting the scooter with the brake lever, I.e the starter button is the brake lever and the brake lever is the start button is this how it works/starts now?

Hi Dieseldog, no problems at all. Just thinking out loud too.
Tried to trace the wiring with a diagram, but wire colors are different.
I can start scooter with a brake lever - don't need to press start button.
The brake wire White/Black going into the loom and changes color at start button. And because I am always getting power on Red/White pin at start button - it's not clear if there is a power from the button. Cos it's all earth with ignition off. The other Brown/Red wire have no power after I press brake lever. So presumably Brown/Red should carry power to starter relay when I press the start button (wire color at the starter relay changes again to White/Black). But that's not the case. Even if I press start button (there is power on both pins) - no power to the relay. I get power to the relay only if I press brake lever.
And jimc, I am aware that ECU grounds the power from the relay, but my test lamp doesn't show voltage on that side of the circuit!? Is that normal?
Any insight appreciated! Paul

I have the exact same issue with that year engine. I've a GTS 125i.e. that i've swapped the motor out with the 2014 GTS i.e. engine I purchased off of eBay. I've installed the ECU/throttle body and when pulling in the brake lever the bike starts and idles however when i give it throttle it dies. Also the red immobilizer light doesn't blink. Did you ever resolve your issue?