Topic: New 750 wire harness installed, dead headlight circuit

[Popwood]

This is something of a ‘75 750 frankenbike. I’ve installed new wire harness and everything is working except the headlight circuit. I’ve triple checked all the connections and they are sound. So, I have no power to the headlight, no power, obviously to the high/low beam switch and no power to the dash highbeam indicator. Headlight lamp is good (plugged it into my 550). From the right handlebar switch, the brn/white is plugged into headlight bucket brown/white multi-connector, the black wire connected to bucket black multi-connector. All fuses OK. I rarely ride at night so can’t remember last time I had headlight on, should that matter. Where do I, how do I unravel this problem? 

[bryanj]

One of the years harnesses needs a jumper wire in the headlamp usually the ones with 3 fuses

[Rayzerman]

Can't comment on the 750 specifically, but my 350F right handlebar switch is grounded via a plate inside that makes contact with the handlebars.....

[Popwood]

I hear about this mystery jumper. I’ve read it’s about 3 inches long. What does it jump, wire color connections? Does it have anything to do with headlight circuit?

[Popwood]

Hmm? While I said in the original post the fuses looked good, when I put a test light on the installed fuses only the 15amp fuse lit up.  should the other two? One of the others is a headlight fuse.

[bryanj]

That suggests you need that "jumper"

[Don R]

 Correct me if I'm wrong, I'm thinking black to brown? Male on both ends. Honda used one wiring harness for all bikes, the US had different lights than most countries.
 Does yours have the headlight on switch, or is it always on except when starting?

[newday777]

This is something of a ‘75 750 frankenbike. I’ve installed new wire harness and everything is working except the headlight circuit. I’ve triple checked all the connections and they are sound. So, I have no power to the headlight, no power, obviously to the high/low beam switch and no power to the dash highbeam indicator. Headlight lamp is good (plugged it into my 550). From the right handlebar switch, the brn/white is plugged into headlight bucket brown/white multi-connector, the black wire connected to bucket black multi-connector. All fuses OK. I rarely ride at night so can’t remember last time I had headlight on, should that matter. Where do I, how do I unravel this problem?

"This is something of a ‘75 750 frankenbike"  ?!!!!! 🤔🤔🤔🫣🫣🫣

Pop this is where it gets Scary! Like Ricky said to Lucy, "Lucy you got some Splanin to do".....
Going to need pictures of your bike and what is Frankenbike about it.

The 1975 year was a one year wonder with some wiring different changes that happened from the right had switches from on K4, then on the K5 and once again then on the K6 and then the K7 and K8 switches and the K5 involves the little jumper in the lighting circuits....
I ran into this on my 75 K5 a few years ago when I had my headlight bucket opened up to do something in there. But What was it??? My rememberer is foggy at this time of the morning in bed without digging in to the bucket of my K5. At first my headlight wasn't working either, got it working. Then after some time past, coming home from a bike night I flipped on the high beam to see further and pop goes my lights at 65 on a 2 lane...Eeek! Thankfully I was riding next to a friend took lead so I could still see to get home.
You posted another thread on the headlight bucket a couple weeks ago and I mentioned there was a little jumper wire in the K5 bucket, did you find it? (that was just as I got the news from my sons that their mom had had another heart attack and then a week later she passed), I just got back home from being out there with them for the funeral a couple days ago and I am busy working on a job so I don't have time to get into my shop to move bikes around and then open up and dig through my K5 bucket, probably until Saturday, to help you through the maze.
PM your number and we can talk on Saturday as I dig it out. I'm in NH so am an hour ahead of you there in OH(?) according to your profile. I have to pack up some tools this morning to head over to the job an hour away fir today and tomorrow.

[Bodi]

When DRL rules came in in a few countries around 1975, Honda deleted the headlight on/off switch but did not revise the harness. A jumper was put into the pod switch wiring cover tube, joining black and brown. It pokes in about 6 inches and can easily be pulled out. No replacement pod assemblies included this jumper.
So male bullets on both ends, plugged in a black and the brown (brown/blue) at the headstock ratsnest.
If you can find the correct country Honda wiring diagram for your year it shows the jumper. The general export version has the on/off switch.
Here's the jumper on a 400F wiring diagram:

[newday777]

When DRL rules came in in a few countries around 1975, Honda deleted the headlight on/off switch but did not revise the harness. A jumper was put into the pod switch wiring cover tube, joining black and brown. It pokes in about 6 inches and can easily be pulled out. No replacement pod assemblies included this jumper.
So male bullets on both ends, plugged in a black and the brown (brown/blue) at the headstock ratsnest.
If you can find the correct country Honda wiring diagram for your year it shows the jumper. The general export version has the on/off switch.
Here's the jumper on a 400F wiring diagram:

That was 1976 in the USA

[Popwood]

Thanks for the info newday and Bodi. To answer some of your questions….This bike does have a headlight on off switch on the right handlebar. The wires in the unit are black, black/white, brown/white, yellow/red and green/red. The starter button and kill switch work fine. In the bucket, the wires black and brown/white attach to the multi connectors for their respective colors. I will include here a photo of a jumper that was attatched to the old harness in the bucket cluster. The jumper is solid brown. Here’s a quesrion: I have Hondaman’s fuse box installed, spade fuses. Using. light tester, the 15 amp fuse will light with key switch OFF or on on both sides of fuse. The 7.5 amp will come both sides with key on and headlight switch in on position, but not in off position. The 5 amp fuse will not light the tester on either side of fuse with the key switch on and headlight switch off or on. This fuse circuit has solid brown wires. I tested continuity for the fuse and a spare, neither lit.

[newday777]

Yes that is the jumper.
The switch has the second position to the far right for the tail "parking light " then you will have the 5a fuse power.

[newday777]

That jumper goes in the solid brown and to the brown w/white stripe. (Notice the white rubber end on that male pin)

[Popwood]

Newday, the brown white coming from the headlight on/off has a male end in bucket. A workaround, I harvested a multi plug from the old harness.  In the new harness I had an unused brown female so used the jumper connect it to the brown white multiconnector. with key switch on and light switch still no headlight. what do you think? 

[newday777]

I'm not able to get to my shop to confirm until Saturday

[Popwood]

Newday, I understand you are busy until Saturday.  PM you with my phone number shortly. Ohio on same time zone as you.  Thanks for your help.

[Popwood]

Someone please explain how this could possibly work; getting power to head light. The headlight switch connects a black wire to brown/white wire when switched on. The head light wires are green, blue and white, green ground, white and blue going to the low beam, high beam switch on the left handle bar. Seems to me there is no power to headlight itself. Wouldn’t the “on” wire in on/0ff switch connect to the white low beam wire in the high/low switch so the light would go on when turned on?

[Bodi]

I believe the on/off switch controls power to the HEAD fuse, and from there it goes to the high/low switch then to the headlight (also powers the instrument lights). If you have an on/off switch the HEAD fuse power should follow that switch and have 12V with it on and none with it off. Then trace what's going on in the high/low switchpod.
Don't rely on unofficial wiring diagrams, I'm yet to find one that is complete and accurate. Use the Honda diagram (owner's manual or service manual) specific for your model, year, and market if you can find one.

[HondaMan]

Someone please explain how this could possibly work; getting power to head light. The headlight switch connects a black wire to brown/white wire when switched on. The head light wires are green, blue and white, green ground, white and blue going to the low beam, high beam switch on the left handle bar. Seems to me there is no power to headlight itself. Wouldn’t the “on” wire in on/0ff switch connect to the white low beam wire in the high/low switch so the light would go on when turned on?

Yep...you've got the VietNam-made RH switch? It's colors was copied from another Honda harness (IIRC the CB350 has those colors?).
The Black wire from that switch should go to a Black wire in the headlight. The Brn/Wht wire should go to the fuseblock (normally on a Brn/Red in Honda's main harness) and return to the headlight as another Brn/Red (in Honda's harness) which goes to the LH Hi/Lo switch. Some main harnesses will have a Brn/Yel from the ON-OFF switch's connection to the fuseblock, then returning to the headlight as Brn/Red, instead.

Aftermarket stripes and wire colors notwithstanding...

If your main wire harness is OEM from the 1975 era, check the colors of the plug into the fuseblock, and see which colors enter the fuses from the left side (of the original fuseblock, not mine). There should be a Red/White (from the battery (+) which will usually be just Red at the 15A fuse (bottom one), then the middle 2 wires will be Brown/Red, and the 2 top wires will be Brown. The hint is: the Brn/Red ones (Blk on my Fuseblock) will be the 7.5A headlight fuse in this version.

Here's the catch: if the wiring harness is a 'blended' version made from the F0 bike (Honda did this sometimes, in production) then the top fuse will be connected to the headlight instead of the middle fuse, and the 7.5A fuse must change positions in the fuseblock. Then you have to trace which wires make that trip, instead, back to the headlight, because they can be Blk/Yel or Brn/Yel instead of a Brn base. This is more common in the K6 than the K5, but I have seen it here in my own garage on K5 before.

The mysterious "jumper" that appears in production bikes usually only shows up in those bikes without the "OFF-ON" headlight switch on the right handlebar. Or in the K6 where the START button only has 2 wires on it instead of 3...and those don't turn off the headlight during electric start, either.