Topic: Headlight headache - stroke of genius or sheer stupidity?

[jtraceypgh]

Having determined my headlight switch was bad (corroded badly) on my 75 750F, I got a used one (thanks Bobby Cleveland!) to replace it.  After running the wires I found the low beam did not work, but the high did.  I did a continuity test on the circuit from the switch to the junction box (not sure if that's the technical term - the wiring box in the front of the frame) and from the junction box to the headlight bucket.  All was well, but still no low beam...

So I made a jumper to go between the Bk/Y (headlight power) and the W (low beam in the bucket) in the junction box, leaving the W that goes to the switch disconnected, turned on the ignition and whala, low beam!  So here's where the "stroke of genius or sheer stupidity" comes in.  I left the jumper in place and tied the Bk/y to the switch on the handlebars via the connection in the junction box to provide power to the high beam.  I now have both, though the low beam is actually hotwired as opposed to being controlled by the switch.  All the connections are temporary at this point pending the feedback I get here...

Be kind, I'm new at this and winging it!   

[dagersh]

It feels great when you can diagnose and fix your own problems.  I just did a very close thing with my '75 550F - man do I feel great! 

http://www.sohc4.us/forums/index.php?topic=25534.0

Anyway, as long as works for you and you can bring it back to correct at a later time, YOU DA' MAN!!!!

Gersh

[puppytrax]

Are you feeding both low & high beam at the same time???      They're both on at once???   

[jtraceypgh]

Uhhh...yeah, which is why after reading some things on the forum I wondered if it was such a good idea...

[OldSchool_IsCool]

If the original function of the hi/low switch was to turn OFF low when hi is on, then it may not be such a good idea.

1- your stator will struggle to keep you battery charged as you are pumping an extra 40+ watts into your headlight
2- the extra wattage may heat the headlight filaments to a premature death
3- the common ground wire wasn't intended to carry the load of both filaments at the same time.

Again, this is IF the switch is intended to run only one filament at a time. 

[tbone]

You could use the switch to trigger a relay to switch from hi to low beam. Re-trace all the original wiring again first. Sounds like a bad connection somewhere.

[TwoTired]

Uhhh...yeah, which is why after reading some things on the forum I wondered if it was such a good idea...

It's not new idea.  But, running both filaments puts almost twice the  heat in the bulb.  Don't be surprised if it turns into a single or no beam, soon.  Avoid bumps on the read as shock will hasten the hot filament breakage.
I think the stock headlight was 40/50 W.  So, running both filaments makes for a 90 watt draw through the main fuse.  That's 7 amps.  Or, the rating of the H/L fuse.  Don't be too surprised if it goes away, either.
It also increases the power draw through the main fuse, too.  When that one melts, the bike won't run at all.

You *could* just get bigger fuses.  But, make certain you are carrying spares with you on your ride.

Cheers,

[dagersh]

Whoops!   I did not catch that both were on at once....  yeah, probably a better idea to fix it right.  You know Ol' Murphy, it will be a no beam when you are out at night!

[jtraceypgh]

Thanks for all the input, guys.  I was originally operating under the assumption that both were on when the high beam was selected.  Sounds like I need to back up and track down the source of the problem to get it fixed right, which was my original plan until I had the brain storm. 

Suggestions?  TT, I read a thread where you were extremely helpful with such things, could I get some of your time in trouble shooting?  I have an analog multimeter and some basic understanding of wiring...

[TwoTired]

Assumptions:
You have a bike wired as described in the Cb750 Honda Shop manual Wire diagram Pg 248.


The switch gets power from the fuse via the Bk/Y wire.
The bar switch then routes this power to the White OR the Dark Blue wire depending on the Lo/Hi position of the switch.
To prove the switch is functional, set your meter to read volts and confirm indication by placing across the battery terminals. 
leave the Neg (usually black) probe attached to the battery NEG terminal.  Use an insulated extension jumper if necessary.

Turn your key switch on.
With the red probe verify 12 V at the Bk/Y connection going to the bar control.
Then verify the dk Blue wire has 12V with the lighting switch in Hi.
Then verify the white wire has 12V with the lighting switch in Lo.

The White and Dark Blue wires then route to the Headlight plug bullet connectors.  Check for 12V there.  And then check at the plug itself.

If at any point in the probe chase you lose 12V, you know there is a break in the path to be corrected between the access points.  You can jumper around the break to verify, or examine the section with careful visual scrutiny to find the trouble cause.

There are other ways to trace trouble cause.  Using an ohmmeter, for example.  If this method is more to your comfort.  Let me know.
If something above confuses you, let me know.

Cheers,

[jtraceypgh]

Thanks TT.  Sounds pretty straight forward.  May take me a couple days to get to it. 

I don't have the manual you refer to and am not sure what the POs did, but have just done color to color for any repairs I've made thus far (except the temporary jumper). 

One thing I do have a question about is there appeared to be two sets of white wires that run from the left control, one shorter and one longer.  One receptacle is a double female, one of which is empty, the other (which I now know goes to the headlight bucket) is a single.  I kept track of which went where when installing the new control, but am curious where the other one runs and if that could be part of the problem...but I digress...will get back to you after I check the circuits per your instructions.

Thanks again...

[TwoTired]

Dunno about your white wire mystery.  The Wire diagram shows only one white wire from the bar control.  Could you be mis identifying the Light Green Horn Wire as a White one?

The LG goes into a double.  The wire into the harness goes nowhere.

Cheers,

[jtraceypgh]

Light green is a very real possibility...

Thanks for clearing that up.  One down...   

Will get back to you as soon as I get a chance to put a meter on things.

[jtraceypgh]

Well, TT, I've finally gotten a chance to follow-up on your advice and troubleshoot my headlight.  Bottom line, it's working as designed.  Apparently there is a bit of a dead spot in the low beam side of the switch, but it's working.  The bike is not currently on the road (waiting for title from ITS), so I don't know how much trouble it's going to be in the long run.  Will have to deal with it once I find out.

Thanks again for your willingness to give a "hand" (you seem to have plenty according to your avatar!) and for all your help!

[GroovieGhoulie]

Had a similar tale a while ago with my 400F:

http://www.sohc4.us/forums/index.php?topic=6784.0

Fixed the wiring in the headlight bucket and replaced the left-hand control, even though the original control was serviceable if I just sanded the rust off the contacts in the switch.

Seems the dip switch sucks moisture and rusts easy, since I've heard about this before from other folks.

Remember guys, do PMCS (Preventive Maintenance Checks and Services) on those switches!

[TwoTired]

If you clean your switches, don't leave them dry.  Unless you find some with gold contacts, they will oxidize again.  Spray the cleaned contacts with DeOX-It so they have a film to keep atmospheric pollutants from reacting with the exposed metal.  Or, coat them with dielectric grease.  The mechanical wiping action of the contact closure displaces the grease for electrical flow.

Cheers,