MOPED ARMY

Yeah your brake light bulb is blown, the battery is only for the turn signals. The ignition runs through the brake light.

I put a brand new bulb in it. Same result.

Here’s the wiring diagram from Myron’s

Someone could have changed the tail light to the one without the resistor also. If that was the case it would blow the brake light though right?

i’ve seen this on minarelli before, there’s corrosion on the contacts of the bulb holder or some other sort of resistance between the ground on the fixture and where the bulb picks up ground.

you can try to isolate this problem with a separate fixture or external wiring, but corrosion on a contact was killing a v1 in exactly the same way you are describing

Let me take a stab at explaining external ignition ground, open for correction. If your brakes are acting like an on/off switch everytime you hit em then your spark is being grounded out.

There are two or more coils under your flywheel that produce power.

They are independant meaning headlight and tail light coil is separate from ignition and brake light coil.

There are two ends of a coil, the hot side which runs to your condenser/points/coil and spark plug. And the other end(blue) ground which runs externally(outside magneto area) to brake switches(2) and to your tail light.

When ground is broken by hitting your brake lever(s) then the path of least resistance is thru your brake light filament to ground which lights it up in the process and keeps spark going.

The entire system is just a few components, not many points of failure. Good wiring, correct working brake switches, clean grounds and operational bulb. An electrical tester and simple diagnostics is sufficient.

Sounds like it has multiple issues. I recommend hardwiring the bike in the simplest possible configuration, then adding in circuits one at a time to diagnose it.

If you have not attempted to bypass the brake switch wires on your brake levers, try that first. Those switches can go bad and cause this problem. Happens on tomos too. If that keeps the bike running then try getting some new switches. There could also be a frayed or pinched wire someplace in the brake wiring that is grounding out.

No they don’t.

Bypassed the switches and runs fine. Hopefully new ones fix it.

You just have to wire out the brake switches! I just ran a wire to complete the circuit. I had to do the same for an older Grande of mine that I just wanted to run.

so you’ve hardwired your brake light off?

if that’s what you did and the bike is running, i don’t think it’s the switches that are your problem.

it’s gonna be in the brake light wiring or corrosion on the bulb socket itself.

use a bit of logic to solve the problem.

so first we’ll do a resting “on” brake switch. in these systems where the other side of the ignition comes in on one side of the switch and ground is on the other side of the switch, a bad switch would keep the bike from running at all because the other side of the ignition is not being grounded.

but, that’s not the case here. the bike runs until the switch is pulled and the connection between the other side of the ignition coil and ground has been broken. when this connection is broken, the other side of the ignition coil now must run back through the wiring to the brake light bulb and pick up its ground after bypassing through the bulb.

now if the other side of the ignition coil can’t get to ground because bulb is burnt out or the wiring back to the bulb is bad or there is a dirty ground for the bulb socket, then the bike will die when the brake is pulled. i bet if you disconnect those two spade terminals your bike will still die right now even with out the bad switch in the system at all.

it happened to us on a v1 microcar after a complete rewire. it took me all of 5 minutes one afternoon to tell my pal how to diagnose it and once we replaced the complete tail light with a new bulb housing, everything worked fine. (edited)

don’t fool yourself, i’m not an electrical engineer.

i just like to solve the problem correctly instead of doing some sort of quick fix if i have the time and tools.

it ain’t hard if you care about winning.

With both the switches killing the engine, and the bulb socket not being corroded, it should be in the wiring. Somewhere.

I did find a ground under the rear fender that was disconnected. I bolted it back on and no rear lights at all. So, with all that taken into account. It should be in the wiring somewhere.