Garelli Tail light mystery

Can someone, who absolutely, without a doubt, please fill me in on the theory of "The Garelli/Italian moped rear tail/brake light circut". I've been staring at this schematic for 3 days and I think I gave myself a lobotomy scratching my head so much. How is it that, when you hit the brake the engine DOESNT shut off? The brake switch ground is attached to the HT coil frame ground. Please tell me how that WONT shut the engine off.

Signed...I forgot..

Re: Garelli Tail light mystery

Darrell Gabbard /

you have what is called a mag coil under the flywheel. one side is soldered on the condensor and the other side is grounded through the brake circuit via switchs that are shorted to the bars until used, then any electricity in the circuit has to follow the least path of resistance. since the mag coil is a shared circuit and produces 12 volts there is more than likely a ceramic resistor that is soldered in parallel around the brake bulb. this ceramic resistor creates a voltage drop in the circuit to where the bulb only needs to be a 6v 10watt bulb and this resistor is low enough to push the remaining electricity through the bulb to ground creating the ignition ground but the resistor is high enough to make sure that the bulb needs to be good because the resistor will not ground the circuit.

Re: Garelli Tail light mystery

Ok there is no resistor anywhere on this thing, would you know what value resistor should be installed? I did stumble upon the garelli books on this website and got schooled up on the theory so, now it's just a matter of Turing it back together and test all my work.

Re: Garelli Tail light mystery

Last line = "putting it all back together..."

Re: Garelli Tail light mystery

Ron Chappell /

K, the resistor in most of these Italian bikes is hidden inside the taillight mounting box - first you take off the whole taillight and then the lens - then you pull off the reflector board (which disconnects the wire clips) and the resistor is mounted behind the reflector board next to the bulb socket. I just went through this with my Motron. It's a typical white ceramic rectangle shape about 2" long. They put it there to keep it our of the weather (I guess).

Re: Garelli Tail light mystery

I already had the tail light assy removed and dismantled then reassembled, it here is no evidence of any resistor ever being there. I suspect it's not original. I'll pick up a resitor and wire it in the mix. Do you happen to know the OHM rating/value should be in there?

Re: Garelli Tail light mystery

I think they are 6 or 8 ohms with a high current rating.

Here's the simplified theory on how this setup works...

There are 2 possible ground paths that can complete the circuit for your high voltage ignition coil. The one of least resistance is a short (0 ohms) to ground through BOTH brake switches. When you pull either brake handle the switch will OPEN and this short to ground goes away. Now is when the 2nd circuit with a path to ground has to be the new path to ground for the ignition coil. The resistance is that of the bulb. If you have a bypass resistor, and the bulb is indeed blown, you need to make sure it does not drop enough voltage to make your coil's spark go weak.

Re: Garelli Tail light mystery

Darrell Gabbard /

look not every ped had a ceramic resistor. most of the tail lights with a duel filament bulb does not have a resistor but are 12 volt bulbs

Re: Garelli Tail light mystery

Put it back together w/o a resistor, everything works as advertised. I had a crappy ground wire at the rear fender ground, replaced the wire and cleaned up the ground, works good now.

Re: Garelli Tail light mystery

i extended the taillight ground thru the plastic sleeve to the HT coil mounting lug.

crappy fender ground eliminated.

Re: Garelli Tail light mystery

Ron Chappell /

hmmm, that's probably not a bad idea - in fact I think I'll do that on mine.

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