Grounding Vespa SI brake lights, this applies to most Italian mopeds.

So if you didnt already know, Vespa mopeds (and most Italian mopeds) have some finicky wiring. They can experience weird issues resulting in loss of spark. It all has to do with your rear brake light bulb being blown out or losing connection. If your bike cuts out when you pull the brakes or has intermittent spark, this is probably your problem. Some mopeds came with a safety feature that killed your spark when your brake light was burned out. It is debatable if that was really a good idea if you own a Vespa lol. On one hand, it is good to have the brake light to be seen but then on the other hand it compromises the reliability of the bike. I say this because I am fixing my girlfriend's Vespa SI and I really dont want her to have to carry tools and extra bulbs on her and have to fix it if it burns out.  With the setup I am explaining you can ground out the brake light and just have a run light on at all time. Also with this setup, your bike will still run even if all the light on your bike burn out. There are more in depth ways to do this but the way I do it leave the bike open to having the brake lights hooked up later and it only takes about 15 mins!

 First thing is you need to make a 3-5 inch wire with a male connector and a 6mm circle end.

 I love shrink wrap.

 Looks nice.

 Blue wire = Brake light. Green wire = Run light.

 I use files to make sure all my grounds will be good.

 Looks ready. Also note that this was painted factory Green over the factory Orange.

 The Black wire is the stock lighting fixture ground. Put the new ground wire you made on the same ground bolt as the Black wire. 

 What the ground wires look like with the taillight assembly installed.

 The very bottom male connector gets grounded and the top male connector gets the Green wire connected to it.

 Using the ground we just created, we connect the Blue brake light wire to it to ground it out. I like this way because you dont have to cut the original wiring harness.

 Everything wired up properly. 

 Brake light becomes your run light.

Done and now the electrical system is more reliable.