Topic: Headlight blowing

[Quorthon]

72 cb500k. 

 I was having some headlight problems with my old sealed beam.   It would randomly turn off and I would have to hit it to make it work.  The high beam also did not work.

I replaced with a new sealed beam wagner unit and high and low beam worked fine while off.

I started it and it still worked fine, then as I was about to pull off I gave it one last high rev and it blew.  I checked it with my ohm tester and it is blown.   The connector gets 12.4-5 volts at idle and up to 14 or so at higher rpms.   The fuse is good. 

 Why did it blow?

[TwoTired]

Is the headlight still mounted as a stock one is?  Is the vibration isolation rubber still there?  Is the rubber still soft?

[Quorthon]

Yes, stock headlight in stock location.  I do not see any rubber anywhere.  Where is it supposed to be?


It blew both the high and low beams while sitting in place and revving the motor.   Didn't seem to be excessive vibration.

[gravano]

You might want to check to make sure your headlight switch isn't corroded and switching back and forth from main to high as you rev your engine.

[Quorthon]

I will.  Would that blow a headlight bulb though?   I was watching the beam while it was working, I was revving it and it wasn't changing.

[gravano]

It's more likely that it would blow the fuse, but it's an easy thing to check.
Good luck.

[raymond10078]

Since your voltage measurements are OK, I'm left wondering if both filaments were on at the same time?  I see it as possible if both filaments were on at the same time, and for too long, that both could open (too much heat).

[TwoTired]

Yes, stock headlight in stock location.  I do not see any rubber anywhere.  Where is it supposed to be?


It blew both the high and low beams while sitting in place and revving the motor.   Didn't seem to be excessive vibration.

The upper fork covers have rubber isolation between cover, trees, and fork tubes top and bottom.  At least they are supposed to have them.  It's a bit of a struggle to get them back on and aligned, so perhaps a PO took the easy way and left them out?

Blowing both filaments at the same time is either shock or overheating or both.  The stock H/L switch is supposed to only have one filament lit at a time.  If both filaments are powered, the bulb can overheat.  If the V reg is maladjusted or faulty, then the revving can make the voltage climb, and that make the filaments draw more current/extra power.  If that is added to having both filaments on at the same time, along with vibration... poof.

Was the headlight really bright before getting very very dark?

Cheers,

[Quorthon]

It did seem pretty bright, which I attributed to the new bulb.  Hmm.   The high and low beams did work fine and switched pretty cleanly between the two.   

I will pull the switch apart and see what it looks like.

Also, it didn't seem to get up over 14.? volts when revved high.  That's normal right?

[TwoTired]

14.5 or 14.7v is highest the battery should be charged to.  Where did you measure the voltage?  At the bulb?  Where were the meter probes placed?

[Quorthon]

Yes, at the bulb plug.   Black to green, red to white.

[Quorthon]

I did some more testing and it looks like the white wire is getting power on low beam and they are both getting power on high.   

So seems to me this means the switch is bad.

I pulled the switch apart and there is no corrosion or anything out of the ordinary looking.


I really dont want to get a new switch and run the wires internally through my clubmans again, ugh.

I think I am just going to unplug the high beam wire and run it like that.

Sound right?

[TwoTired]

If you look at the wire diagram and specifically the dimmer switch function, the switch has a make before break arrangement while passing between the high and low beam selections.  This is done so the headlight won't go dark if the switch is partially bumped.  Anyway check your switch and be sure it is able to move through the full range of movement so that both filaments can't be both on indefinitely.

Cheers,

[scottly]

It blew both the high and low beams while sitting in place and revving the motor.   Didn't seem to be excessive vibration.

Are you sure it really blew, as in melted the elements? That would take a pretty high voltage to do, not just both high and low beams on at the same time.

[Quorthon]

I did check out the switch and looked at the back of it while moving through the settings.   Visually it looks fine.  While there is some slop and slight binding while sliding it, there is nothing that I would think is out of the ordinary.


I have not  made sure the bulb actually melted the filaments, I will take another look, but it is kinda hard to see since it is a sealed beam.

I am also going to take a look at the grounds and make sure they are ok.

Here are some picture of my headlight wiring.  Is there anything that jumps out at you?  Wiring is definitely one of my weak points.

Are these in the right places?


The rest look funny?

[dave500]

umm?has the po fitted a relay thats sticking maybe?so both lo/hi are working?that or the switch needs looking into,,they are fiddly to dissemble but can be done,if you dont think you can take it apart and get it back together dont,if you can find an old switch take it apart for practise.