Topic: Blowing main 15amp fuse

[katman]

As I said in an earlier post, I'm getting my 77 750K back together after an resto. I had to replace the wiring harness
so I got a used one from a another 77. I had to redo the connections in the wire block were it plugs into the
rectifier plug. I may have not got the yellow wires at the bottom of the plug back into there same slots. Will this
make a difference. Every time I turn the key on the 15 amp fuse blows. Any suggestions
Thanks

[Sdsbassist]

Could be lotsa stuff.

had a 77 that blew because an exposed wire would hit the fender.

[MoMo]

If you are referring to the three yellow wires having them out of whack should not matter as they are only the AC output from the stator that gets converted to DC by the rectifier.  You either have a hot wire connected to ground or the problem sdsbassist mentioned...Larry

Bad harness, key switch, fuse box

[katman]

what color are the hot wires usually

[MoMo]

Red from battery and black out switch are the two basic hot color...Larry

[katman]

Okay,
Everything seems to be connected correctly following my wiring diagram. Tried another fuse block and rectifier.
Still blows main 15 amp fuse when key in switched on.

[katman]

Okay,
Looked over the whole harness and found nothing amis. Must be a break behind the covering. Do the green headlight
grounds go to green in the headlight.

[MoMo]

Do you have the original switch or an Emgo aftermarket?...Larry

[Black 750K8]

what color are the hot wires usually

Maybe this will help.

More from Jonesy:

(I put this together after a few questions about the wiring in these bikes. Some suggested this be put in the FAQ. Hope this is helpful.)

Here’s a general wire guide for the 70’s Honda SOHC/4’s. Some of this may be different for the 650 (I’m mostly familiar with the 350, 400, 500/550 and 750) or bikes factory-equipped with electronic ignition. Consult your manual for specifics.

Main Color/Tracer Stripe Color- Description (Approximate Path, if Applicable)

All Circuits
Red- Constant Hot From Battery (Battery Terminal-Main Fuse-Key Switch)
Black- Switched Power Supply Buss (Throughout motorcycle)
Green- Ground (Throughout motorcycle)

Lighting
Brown- Tail Light Power (Main Switch-Tail Light)
Brown/White- Instrumentation Backlighting (Lighting Switch-Instruments)
Orange- Left Turn Signals (Turn Signal Switch-Front/Rear Signals)
Orange/White- Left Front Marker (Light Switch-Marker Lamp)
Light Blue- Right Turn Signals (Turn Signal Switch-Front/Rear Signals)
Light Blue/White- Right Front Marker (Light Switch-Marker Lamp)
Gray- Pulsing Power for Signals (Flasher Relay-Turn Signal Switch)
Blue- High Beam Power (Hi/Lo Switch-Headlamp/Indicator Lamp)
White- Low Beam Power (Hi/Lo Switch-Headlamp)
Brown/Red- Fused Headlamp Power (Fuse Box-Hi/Lo Switch)

Ignition
Black/White- Coil Power Supply (Cutoff Switch-Coils)
Yellow- Breaker Signal, Cylinders 2&3 (Right Points-2&3 Coil)
Blue- Breaker Signal, Cylinders 1&4 (Left Points-1&4 Coil)

Starting/Safety/Monitoring
Blue/Red- Oil Pressure Signal (Oil Pressure Switch-Indicator Lamp)
Red/Green- Neutral Switch Signal (Neutral Switch-Indicator Lamp-Safety Unit)
Green/Red- Clutch Switch (Safety Unit-Clutch Switch-Starter Button)
Green/White- Horn (Horn Button-Horn)
Yellow/Red- Solenoid Signal (Starter Button-Solenoid/Safety Unit)
Green/Yellow- Brake Light Power (Front Brake Switch/Rear Brake Switch-Brake Light)
Brown/Blue- Turn Signal Pickup (Turn Signal Beeper-Turn Signal Switch)

Charging (3-Phase External Excitation Systems)
Yellow- Stator Coil Output (Stator-Rectifier)
White- Field Coil Supply (Field Coil-Voltage Regulator)
Red/White- Positive Rectifier Output (Rectifier-Battery)

**NOTE- I pieced this together from referring to wiring diagrams I have. This is meant as a general guide and will vary between models/years. If anyone spots an error or omission, please post it and I will correct it. Thanks**

A few more thoughts that may help people:

Another learning I found useful in troubleshooting various circuits was knowing which sides of the circuits are impacted by switches, etc. Typically, most circuits on these bikes can be thought of as having 2 "sides"- a "hot" side (power from the main buss activated by the key switch), and a ground side. For example, the lighting on these bikes (head, tail, gauge, running and turn) is all controlled by a switch (or switches) on the hot side of the circuit, while the ground side of the circuit is always complete.

Basic Circuits controlled (switched) on the HOT side of the circuit:
-Headlight (Both Hi and Lo Beam)
-Tail Light
-Brake Light
-Turn Signals
-Marker Lamps (if equipped)
-Starter Motor (heavy-gage wiring switched by the solenoid)
(Note: while they don't break circuits under normal circumstances, the fuse(s) are all located on the hot sides of their respective circuits.)

Basic Circuits controlled on the GROUND side:
-Neutral Light
-Oil Pressure Light
-Starter Solenoid
-Horn
-Starter Safety Unit (As best I can tell, all sensors are on the ground side)

Special Case: Ignition
Under normal operation, the ignition coils are activated by the breaker points, which are on the ground side of the coil circuits, as the coils are fed constant battery power while the points interrupt the ground side. However, the emergency cutoff switch is located on the hot side of the circuit, coming into play by cutting the battery power to the coils.

And, That Age-Old Question...
...Does it matter which order I connect the yellow wires coming from the alternator to the rectifier? No. There is alternating current being carried by these wires and the diodes in the rectifier take care of sorting out the positive charges from the negative ones.

[katman]

Thanks for the breakdown, and I'm running the stock switch.