Topic: Head light stopped working......huh?

[dylboss]

So, was driving the other day and the head light just stopped working all the sudden.  Thought it was a bad bulb or something, so I pulled it.  Tested the circuit with a modern bulb I pulled from one of my other newer bikes that had the standard 3 prong connection.  Still nothing.  I don't get it.  All the wires look uncorroded, and all the other electrical stuff works fine, blinkers, brakes, indicators by the tach/speedo.  All fuses look fine too.  Any ideas?

Thanks.

[TwoTired]

The starter button/switch has a headlight interrupter.  If the switch disintegrates (usually caused by a leaky master cylinder sometime in it's life), The switch gets weird, sometime the headlight stops sometime the starter stop working sometimes both.  The switch plastic holds the contacts in correct orientation as long as it intact.   If not, random things happen.
Check out a wire diagram for a 78 Cb550.  Toss the Clymer.

Check for power out on the Black/red (I think) from bars to headlight fuse.  If dead, curse the bar switch.

Cheers,

[Spanner 1]

The old 'fuses look fine' syndrome again  ..... Here's the thing, the h/l is on a fuse all by itself and everything else will continue to work fine if the h/l fuse is blown..... very likely the fuse is broken under the cap where a visual inspection will not reveal the problem. The fuse  blowing this way is caused by A. it being prolly 30 yrs. old! and B., subject to many, many heat-up and cool down cycles  due to a corroded fuse holder,even, as Two Tired says , the corrosion can be 'transparent'.  Time to polish the fuse holder, put a new 7A h/l fuse a new 5A tail fuse and a 15A main fuse in their positions, Be shure each fuse is a tight fit in its clips and undo the 2 screws on the fuse holder to look at the connections on the backside too.... good luck 

[dylboss]

thanks guys.  I'll check the fuse stuff first, before I start chasing starter button/switch issues.  Sounds a heck of a lot easier.   

[madmtnmotors]

The actual headlight switch on my CB750K8 was the culprit for me. I was able to nurse my headlight switch for a while but finally had to replace it. I don't know if the 550 is similar, but I wasn't too happy with the Honda switch, especially the "Always on" feature. Found a 3-position micro toggle switch at Radio Shack that actually fit in the stock switch position, so now I have an off position. The switch has held up well, even in wet weather.

[dylboss]

The actual headlight switch on my CB750K8 was the culprit for me. I was able to nurse my headlight switch for a while but finally had to replace it. I don't know if the 550 is similar, but I wasn't too happy with the Honda switch, especially the "Always on" feature. Found a 3-position micro toggle switch at Radio Shack that actually fit in the stock switch position, so now I have an off position. The switch has held up well, even in wet weather.

Good to know.  Thanks.  Maybe i'll tear apart the switch tomorrow to inspect.

[madmtnmotors]

You might want to try isolating the problem with a meter first. You should be able to check your switches from the wiring in the headlight bucket. Find the switch leads, disconnect the from the harness (so you don't fry the ohmeter) and check for continuity across the switch with an ohmeter (or continuity tester) in both the high and low positions. Jiggle the switch side-to-side while your at it to see if you can get momentary contact. If you seperate the switch housing , at least check for continuity across the switch, AT the switch (with power off, or at least disconnected), before tearing the switch itself apart. Things are pretty tight in the switch housing and can be difficult to disassemble/reassemble, so bring your patience. Electrical problems can be maddening, but a methodical approach, eliminating the possible causes one by one has served me well.

Bring your patience!

[dylboss]

You might want to try isolating the problem with a meter first. You should be able to check your switches from the wiring in the headlight bucket. Find the switch leads, disconnect the from the harness (so you don't fry the ohmeter) and check for continuity across the switch with an ohmeter (or continuity tester) in both the high and low positions. Jiggle the switch side-to-side while your at it to see if you can get momentary contact. If you seperate the switch housing , at least check for continuity across the switch, AT the switch (with power off, or at least disconnected), before tearing the switch itself apart. Things are pretty tight in the switch housing and can be difficult to disassemble/reassemble, so bring your patience. Electrical problems can be maddening, but a methodical approach, eliminating the possible causes one by one has served me well.

Bring your patience!

Thanks Madm.  Patience is not one of my virtues, but I'm working on that  .

[bollingball]

Madmtmmotors Do you have a part # for that radio shack Sw.?

[madmtnmotors]

Well, looks like Radio Shack no longer carries the same switch that I used. I guess things change in 15 years. Radio Shack now only carries the single pole version of this switch but I was able to find it here:

http://www.scootersperformance.com/zen/zen-cart-v1.3.8a-full-fileset-12112007/index.php?main_page=product_info&cPath=2_51_62&products_id=186

There may be other sources on the web, but this is the first one I found. Things are very tight in the switch housing, and I may have had to enlarge the switch opening ever so slightly. A well few well place swipes with a round file would likely suffice if necessary, it's been so long since I installed this switch I can't remember exactly what was involved. I do remember soldering the leads to the switch with very short bits of heat shrink for each connection to the switch and possibly rtv silicone (or liquid electrical tape) to help weather proof everything prior to reassembly. TEST FIT EVERYTHING BEFORE CUTTING WIRES! And make sure this is what you really want to do, hopefully verifying that the switch is indeed the culprit before attempting to to do this modification. Here's what mine has looked like for so long that I almost don't remember what it looked like with the stock switch:

[madmtnmotors]

Here is the listing for Radio Shack:

http://www.radioshack.com/product/index.jsp?productId=2062486

Indicates "Out of Stock" online but also indicates "Available at most stores".

Single pole, Double Throw (SPDT) with center "Off" position is the one you would need. A Single pole, Single Throw (SPST) won't accomodate Hi/Low.

[dylboss]

Thanks to all for the help.  Turned out to be a bad connection at the fuse.  Sanded the connection points and all is working.

[Spanner 1]

 

[madmtnmotors]

Glad to hear you found that problem and that it was not the switch after all (because replacing mine was a PITA). Them electrical problems can try your patience, which is why the methodical approach of eliminating what is NOT the problem works so well.

[kingj6]

The old 'fuses look fine' syndrome again  ..... Here's the thing, the h/l is on a fuse all by itself and everything else will continue to work fine if the h/l fuse is blown..... very likely the fuse is broken under the cap where a visual inspection will not reveal the problem. The fuse  blowing this way is caused by A. it being prolly 30 yrs. old! and B., subject to many, many heat-up and cool down cycles  due to a corroded fuse holder,even, as Two Tired says , the corrosion can be 'transparent'.  Time to polish the fuse holder, put a new 7A h/l fuse a new 5A tail fuse and a 15A main fuse in their positions, Be shure each fuse is a tight fit in its clips and undo the 2 screws on the fuse holder to look at the connections on the backside too.... good luck 

Where is the headlight fuse on a 1978 Honda CB 550K?

[LesterPiglet]

With the others. Under the left side panel. 4yo thread, not bad.