Headlamp Bulb Problem

[Flathead Butch]

Greetings on a cold North Carolina Morning,
My carb is being rebuilt as part of my winter prep for next seasons riding and other troublesome little problems are being addressed. My 35 VLD is still 6 volt with all new wiring. The headlamp is an original Cycleray (I assume it came with the bike). The problem is it keeps burning out the bulb. It works for several runs, either the high or low beam goes out shortly followed by the other. What is the most likely source of the problem? Or how does one go about finding the source? Thanks for your help and tolerance of a woefully ignorant latter day biker!
Butch

[bselph]

On my 33VC I discovered that I had a bad ground on the battery. The bulbs would blow out sporadically. Totally by accident I blew a fuse on the positive side of the battery and when it happened, the bulb burnt out. While fixing the cause I found the bad ground and I have not lost a bulb since. I would check all of your grounds.

[Flathead Butch]

Will do so and thanks for the reply.
Butch

[Jerry Wieland]

#1 cause of excess burning of bulbs is high or low voltage. Many possible causes - Bad battery, wrong generator output, wiring shorts and opens, etc

Jerry

[exeric]

On my 33VC I discovered that I had a bad ground on the battery. The bulbs would blow out sporadically. Totally by accident I blew a fuse on the positive side of the battery and when it happened, the bulb burnt out. While fixing the cause I found the bad ground and I have not lost a bulb since. I would check all of your grounds.

I had the exact same problem with my Chief. Like Bob said, it was a bad ground and once I remedied the poor contact, I never lost another bulb.

[Steve Slocombe]

I'd also start by checking the ground connection. Pre-1935 Harleys were grounded through the forks but Shop Dope 130 of May 8, 1935 says 'Difficulties reported now and then such as repeated burning of lamp bulbs...have indicated the probablities of an occasional motorcycle with faulty ground through head fittings. To be sure of every motorcycle having positive ground hereafter, we are now...running a separate ground wire directly from grounded terminal of ammeter (left side terminal) to motorcycle frame. Ground wire is attached to frame with the screw that secures control coil clamp on left side of frame head'. (This is part 3344-25). 'We encourage installation on all motorcycles not so equipped originally.'