M38 headlight burnout

warsawillys · Post by **warsawillys** » Tue Aug 16, 2011 8:44 pm

I have gone through two left side 24V headlights on my M38. I thought the first time it was a defective bulb but now I think I am the dim bulb. It worked fine when I installed it and check it out. It continued to operate for about 10 minutes then poof.

What could cause the bulb to burn out? The only thing I can think of is for it to get more than 24V but how can that happen? If it is the regulator, why wouldn't the other side burn out too? Any ideas out there?

Don

Post by **wesk** » Tue Aug 16, 2011 10:51 pm

Check system voltage with a digital volt meter. Should be 24 to 28.5 with the engine running around 2500 RPM.

Check all connectors for corrosion. Check for bad grounds. Corrosion and bad grounds will give you a higher resistance and lead to a hotter running filament.

Use a good Ohm meter to check for a good ground from the lamp's ground wire connector all the way to the frame.

warsawillys · Post by **warsawillys** » Thu Aug 18, 2011 6:26 am

Thanks Wes. I'll check it out. Bad ground would not be surprising.

Don

warsawillys · Post by **warsawillys** » Tue Sep 27, 2011 7:03 pm

Hi Wes....looks like I might have a high voltage issue....I get 30.5V from the headlight connector to ground on a digital meter when running the engine around 2000 rpm.

It puzzles me that I haven't burned out the other headlight after going through several on the one side.....maybe it has a slightly tougher filament?

I also checked the ground and it looks solid as far as I can tell.

Is this a regulator or generator problem (or dumb owner problem)??

Don

Post by **wesk** » Tue Sep 27, 2011 9:31 pm

You need to adjust that regulator to 28.5 Volts.

For the over-voltage to consistently burn out only one lamp on one side means that lamp has a high current rate issue the other one does not or that lamp is not mounted as tightly as the other and the filiment is weakened by vibration.

Are both your headlamp buckets oriented the same for the bulb tab index? If not you may have a filament mounting orientation issue. Most filaments require horizontal orientation and if mounted towards a vertical orientation will generally fail early in life.