Failing Headlight Dip on a CB550f

[MickP]

This is very much a newbie question but I can't figure it out by myself... I have a '79 CB550f, I can't get the headlight to switch on to full beam. I checked the fuse box and the previous owner has installed fuses that are above what they're supposed to be- for instance the 7a fuses were replaced with 15 ones, and where the 15a fuse should have been someone had stuck a 35a fuse there. Not the kind of thing you normally check when you buy a bike and I've only done a few miles on it. The main beam was operational when I got the bike and it's sat covered in a dry garage for about four months- criminal I know... but I do run it twice a week.


Anyway, is this fuse situation this likely to be the source of my problem or am I missing somehting even more obvious? I'll admit that I haven't actually taken the headlight apart, but the lamp works on dipped beam and the park lights also work so I'm guessing the bulb itslef is fine. Any suggestions would be really helpful!  Ta

[SteveD CB500K0]

The headlamp bulb is a dual beam so it is quite possible that the high beam filament is blown. Easy to test.

The fuse thing is a bit more worrying. Put standard values back in and see what happens.

[MickP]

Thanks man, no luck yet though

OK, I put standard value fuses back in, nothing changed. I then checked the bulb which looked fine, but I removed and replaced it anyway. At some stage someone's replaced the standard fitting bulb with a modern three pronged halogen bulb like the one below (far left), the wiring looks to be original although it's hard to tell. The park lights and low beam are running off a seperate bulb located below the main light so they're completely seperate.

Am I right in thinking that this has happened because of the non standard value fuses that were installed previously? Something somewhere has obviously bitten the dust but I have no idea what it'd be, I doubt very much that it's the switch itself as it was working fine a few months ago and has been used little since then.

Ah, frustration...

[Bryanj]

Doubt its anything to do with a fuse value, more like a corroded connection or switch

[florence]

Do not worry about the fuse problem at this stage.  Sometimes people put any old value fuse in if they don't have the correct one to hand.  I know that is not the correct thing to do but it happens.  Simply put the correct fuses in place and forget about them.  They do not affect what happens in the wiring, they just protect it from surges; instead of your wiring setting on fire, the fuse simply blows.

Consider the bulb problem.  The three pronged bulb is the standard fitting for this bike; it is the same as fitted to mine.  They have two filaments, one for dip, the other for main beam.  Put a multimeter on the bulb and check that both filaments will let a current pass through them.  

I have found that the most likely cause of failure apart from bulb blowing is the connector, where it goes into the bulb.  Try gently bending the prongs of the bulb outwards so that they make a tighter fit in the connector;  it only needs to be a small amount however.  If this does not work; get a multimeter and check for current in the connector.  Scrape the  meter probes on the metal to ensure you have a good connection.  If this fails then work your way backwards through the wiring system until you can find out where it does work.  Look at the wiring diagram if that helps you and just think of it like plumbing.

Work on one part at a time and do not think about the spaghetti of wiring otherwise it becomes too daunting.