Motobecane 12V Headlight Dim

I've been restoring my '79 50V and it is running really well at this point. The only challenge I have now is that my headlight is burning really dim even at full power. I have a new/correct 25W 12V GE sealed beam and new correct tail light bulb (which is working fine). My speedo lights are not working and I have bypassed my broken headlight switch as shown in the attached diagram (provided by Shaun, Myron's Mopeds). Could this be the issue?

Any ideas on where/how to trouble shoot this problem? Thanks!


Re: Motobecane 12V Headlight Dim

try to disconnect the bad speedo bulbs, one may be partially shorting out sending power to ground.

replace the connecting block near engine with a new one, or wire nuts. the old connecting block is ridiculous in design, and prone to getting alot of muck in it.

examine wiring throughout the bike looking for pinched, or damaged wires. check all connections inside the headlamp casing.

All of mobies use lower watt bulbs than that (6v-8w, 12v-16w aprox.) allthough if anything, that should be brighter. I might be concerned about it draining too much power.

I do not know about that diagram, but I removed a bad switch from my system. I simply looked at what connections where made with the switch in each position, and wire nutted together the wires to replicate the on position.

Good luck

Re: Motobecane 12V Headlight Dim

I meant to say all of MY mobies use lower... -not- All of mobies use lower....

many mobies from different years, models, or country of sale have different headlamp ratings

Re: Motobecane 12V Headlight Dim

imwayl8 /

Thanks for the tips Dan...I'll give 'em a try!

Re: Motobecane 12V Headlight Dim

Thanks for the post of the diagram. My moby(12V) keeps burning out brake lights! All my other lights are working fine so I have trouble understanding why such a heavy load is burning out the brake light.

Maybe I will wire all three in the diagram and see what happens. Atleast then it won't die if the brake light goes.

By the way, I use a P21W bulb for my moby, nice and bright. My moby is not using a sealed beam setup though.

Re: Motobecane 12V Headlight Dim


I took a look at the wiring diagram for your bike - in typical motorcycle / moped style, the diagram shows what gets connected to where, but gives little useful info on troubleshooting. Important details are left out of the magneto and light switch wiring.

What I'd suggest, is checking the AC voltage between the white wire at the taillight, and frame ground. Then compare this to the voltage between the headlamp terminals. They shoud be the same.

If not, you've got a bad (high-resistance) connection in the wiring, probably local to the headlamp bucket, or the associated grounds. It appears that the lightswitch supplies power to both the head and tail lights from a common point - so if the tail is getting good power, the switch should be OK.

If the issue was a headlamp of too high a wattage, I'd expect the tail lamp to also be dim.. since they share a common feed.



Re: Motobecane 12V Headlight Dim

for those who do not have it, here is the wiring diagrams, and much more

Re: Motobecane 12V Headlight Dim

Argh, I ran into the same problem last night!!

Did you ever find an answer to this??

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account