Topic: what could have caused this?

[78whiteorbs]

The rectifier got fried before, which fried the green wire on your new harness. Using a temp probe is not really the proper way to locate a short, since by that time even more damage is done.

No I wasnt using a temp prob for that. I was using a multimeter set to test continuity by tone. I used a temp probe because the fuse felt especially warm.

[bryanj]

Those fuse boxes, when they get old, are notorious for the clips getting corroded and a loose fit, so much so they can melt the plastic housing and damage the wire connection on the back making it even worse.
Polish the inside of the contact clips and make sure they fit tight on the fuse end, in bad cases replace the fuse box. Most people who do that replace with a blade fuse type.
The black red wire in rh switch should connect to black with starter button released and disconnect when button pushed.
Blue wire goes to headlamp main and blue idiot light(main beam indicator) and should have a resistance not a short. Toning is not a good test you need to measure ohms.

[78whiteorbs]

Yeah knew about the blade fuse block up grade...Does Hondaman sell those?


What does that black red wire do? What's it for? I got no power to headlight ,green(ground), white(lo) or blue(hi).

I was tracing a short that melted my groundwire in seconds. I didnt replace the rectifier  when I installed the new harness as I assumed that circuit was fused but later found out it was not.

Gonna replace that melted wire in the new harness and replace the rectifier and see if that does it.
When I checked the hi beam indicator light was blown too of course.

[bryanj]

Tell me where the other end goes in the switch and i will give you a guess

[PeWe]

Circuit diagram is a must when installing the harness and verify each wire when connecting it.
There are diagrams for download.
http://manuals.sohc4.net/cb750f/

[78whiteorbs]

Peewee I did use a diagram- everything went were the old one was removed. Only 3 extras by the rectifier on the new harnessdont know what they are for. I've I stalled new harnesses before and was pretty straight forward everytime.

[ekpent]

 There are 3 wires that go to the starter button on the 75F. Look on the wiring diagram. When you press the start button it shuts off the headlight to save juice I guess. Black is a power wire.

[78whiteorbs]

Right that's what I was thinking it was. The headlight wires are not getting voltage. I do know that. The bike starts and diesnt melt wires fine as long ad the black with red tracer wire from the starter switch is disconnect from the  starter switch. .maybe that's why no juice to headlight...ah, man I hate electrical probs!

What's the methodical approach here...hellp me out guys. Replace the prolly fried rectifier, that's a given....next...
.
I honestly thought to buy a new set of bars with pods to try and eliminate that from the equation which funny in a way.

[seanbarney41]

try cleaning the starter button with some spray contact cleaner.  If you have to try and take it apart, the plastic is likely to crumble so be careful.  Good thing is pretty much every U.S. market honda from 76-80 or so uses the same right hand control.  Only the wire length varies.

[HondaMan]

Yeah knew about the blade fuse block up grade...Does Hondaman sell those?


What does that black red wire do? What's it for? I got no power to headlight ,green(ground), white(lo) or blue(hi).

I was tracing a short that melted my groundwire in seconds. I didnt replace the rectifier  when I installed the new harness as I assumed that circuit was fused but later found out it was not.

Gonna replace that melted wire in the new harness and replace the rectifier and see if that does it.
When I checked the hi beam indicator light was blown too of course.

Yep, still make them.

The Black/Red wire comes from the Headlight fuse in the fuseblock. This headlight fuse is supposed to get its power from a Black/Brown (some are Black/Yellow) that comes from the un-pressed contact of the START button. This power disappears when the START button is pressed, diverting the power instead to the Start solenoid while killing the headlight.

[bryanj]

I asked to confirm where it goes because there are aftermarket switches out there with the wrong colours  going into switch then the diagram is useless!!!

[PeWe]

I should disconnect all connectors and check everything, functions and look for short cuts. Easy that a connection in handle bar switch shorts to bar or switch housing

Very important to verify each lead on an aftermarket switch where colors are not always exact. Not even switches in a Honda labeled box.
Verify function with a buzzer and mark each wire with tape and note.
Compare with diagram which is a must to follow when working with the electrics.

One thing that usually is missing is the jumper cable from black to brown/white to get the gauges to shine. I do not know if all CB's have that.

Verify everything before connecting battery. At my last build I connected battery plus via an auto multimeter reading the current, a few amps OK feeding coils and light added more when switched on.
Feel if any wire becomes hot was not good enough.
All cabling was new on that bike, aftermarket switches and main harness.

[78whiteorbs]

Thanks for the replies fellas. Ba k at it tomorrow....the control switch appear stock to me. My hunch is that right pod is shorting In the housing or bars but of course have no way to quantify this so I'll be digging back in tomorrow. Cant wait to mark this solved!

[PeWe]

With a cheap automotive multimeter you can measure the current to see where the problem is.
DC 20A

Dwell 8cyl 23-24.4 degrees for CB points gap setting while idle.
Diode tester for rectifier. The diode work in one direction which is most important to verify. Usually 3 diodes in same direction, 4th opposite.  CB750 shop manual ch.8 describe details of rectifier.

Something like this
https://www.ebay.de/itm/352778367986