Bulb blowing

I'm going to post on LCGB as well but here's the problem. very bright brake light at tickover and as soon as the revs rise the bulb blows. new switch fitted when rebuilt. I've disconected the pink from the stator and bridged across from the horn circuit (orange) and all works as it should, indicating a short or something in the wiring or coil for the brake light circuit. I've removed the stator and stipped the outer wiring sheath off. No signs of a short here. How can I test the coil itself? All the coils are in circuit so a simple test lamp is no good. Anyone know what ohm rating the coil should be. Can it be tested without unsoldering it.

Thanks, Paul

Hi Paul!

A common problem with 6v Lambretta's (Luna or otherwise) is bad earths, the stator pumps out various voltages and a standard system "floats" so the the voltage and current can be all over the place, it's only proper earthing that keeps things in balance. Luna's from new didn't have much return electrical continuity, so separate earths for rear light, coil, headset etc. are a must. I don't think you need to worry about the coil resistance, they probably aren't the problem.

Eventually after much mucking about with my Vega (and also my 12v GP) I added an earth wire direct from the stator and created a new junction point in the electrical junction box using car crimp bullet connectors. (Note, this doesn't fit under a standard Vega rubber cover, you need to use an S3 deeper type). This then connected to the rear light, coil and headset, effectively by-passing the frame (earth return) system. Look out also for HT leakage on the rear light, I found this when I removed a blown rear bulb with the engine running and got blue lightning sparks.

I hope this helps, remember Vega's where designed down to the very cheapest manufacturing solution. When you do get it working without blowing, the lights will be like anemic glow-worms

Thanks for your reply. What you say makes good sense but I don't think this is the problem. I do have good earth. It would not explain, unless someone else corrects me, why the bulb shines so very bright before blowing. I will try a seperate earth anyway. Back in the late sixties/early seventies I had two Vegas, one was the only brand new lambretta I ever bought, and used them as daily transport. I never had a problem then. If anyone else has a theory I'm all ears!.
Thanks for your time,

Paul

paul, was the switch tested first? i know you say it was new, but i have had these from new before and not work.
was both the bulb fillaments illuminated?
have you got the right wattage bulb in?
vibration also plays a part, this can lead to bulb blowing.
the back light and the light/numberplate holder are all in need of a good earth, just check if your machine has been repainted etc.

Daz, all the points you raise have been checked and are as they should be. I'm putting it all back together today and I'll report back but I haven't found anything wrong. I think it is the stator coil for this circuit. By the way what does the coil with the purple wire power? Looking at the wiring diagram it has a 'gap' in the coil with no continuity across it when tested with a simple test lamp. Likewise what does the coil with the brown wire power? Both seem to go to the 'lights' part of the handlebar switch.

Paul

paul from memory purple is lights and brown is power to switch

Daz, Gordon, I'm eating a massive slice of humble pie! I did have the two wires to the rear light the wrong way round. All good now. It only goes to show that after all these years a simple schoolboy error had been made and I had convinced myself I had the wires on the correct terminals. I started to doubt myself when I was working on a series 3 the other day ( the terminals are colour coded ) and just out of interest I changed them over and the bulb blew when revved up just like the Vega. I'm sorry for wasting your time with this post but maybe down the line someone else will have learnt from my stupidity.

Paul.

paul, alls well that ends well, glad you got it sorted out, did you not see the pink and black spots on the vega back light terminals?
dont worry about making stupid mistakes i have made loads