omg gremlins! i swear i didnt feed them after midnight

[jlew]

first off -

1980 DOHC CB750C 'Custom'

I've had the bike a decade or so; recently started giving me electrical problems.

The issue i'm having is screwy brake light/blinkers.

with the bike running i have running lights and brake light/headlight.

depress the brake and the brake light doesn't illuminate any brighter
signal turning left and left blinkers go out, right stays illuminated
signal turning right and right blinker goes out, left stays illuminated

I've pulled off the rear brake and signals and checked over the wiring and sprayed connectors and buffed up the ground tab.

I've checked the brake switch for continuity- good to go.

rear wiring setup:
rear brake has 2 lights with a G/Y (grn/ylw) and B (brwn) and a common ground to the fender.
rear right has BLK with a light blue marker
rear left has BLK with an orange marker
i'm assuming the ground is IN the blinker housing

front bucket setup:
open up the headlight and OMG its NOT a rats nest. the connectors were even still in their clip-hold locations.
the ground there is buffed and good.
right turn - BLK with a light blue marker and BLK with a light blue/white marker
left turn - BLK with an orange marker and BLK with an orange/white marker


so where would i even start? (fuses are good) grounding issue someplace?

 

[mydlyfkryzis]

Behavior like that is bad ground. The blinkers usually have a ground wire from the mount to the chassis.

Get a jumper with alligator clips. Ground the offending blinker/brake light, see if the issue goes away.

The existing ground wires may have corroded where they connect to the chassis, or the chassis to battery ground may be an issue.

Time to go through the wiring, dielectric grease connections after cleaning them up.

Honda grounds are wired, so issues like this come up when one or more of the wired grounds don't make it to ground.

I'd start at the tailight. If your bike is like most Honda's, there are 2 wires to the tail light, and the taillight housing has a separate ground wire.

 

[jlew]

back from vacation yaaay. its now like 100 degrees when i returned, snow when i left?? wow Iowa weather rules. itching to get riding!!!!

anywho I've pulled my wiring harness trying to chase down this elusive ground. some wires are junked so i'm patching terminals as i go along.

I'm finding that the black/white wire from the spark units has continuity to ground when the spark units are plugged into the harness. black/white runs up to the start/stop/run switch.

i have no idea when it comes to electrical. anyone care to shed some light for me?

 

[jlew]

wow this harness has some CRAZY shit going on.

so on the frame ground its spliced 5 times, and there are 3 grounds running off of it that arent connected to anything and under each splice there are 2 'clipped' wires that were still soldered. is this from the factory or can i assume the PO did a nice hack job?

so i'm replacing one wire at a time, but to slim down the harness whats the implications of just cutting the ground on each plug on the harness side and running that to the frame (see pic)

 

[notlob]

The honda 750 harness has quite a few dark green earth cables with multiple joints in throughout the harness. A wire may have corroded or come loose from the crimp. I would check the bulb holder and the earth to that first, if corroded there you wont get a good earth and the same problems you described.

 

[mydlyfkryzis]

I ran a separate, heavy gauge green wire from the mounting bolt of the reg/rect to the negative terminal of the battery.

There are too many points between the tool box and the battery - terminal that may not conduct well.

Bad connections are best fixed with new connections.

 

[jlew]

Went through and reworked a 'draft' harness. Got new 4/6/9 pin connectors and terminals and snap connectors in the mail today, waiting on a few for colors in wire to arrive before I wore up my final.

Basically stripped the harness and consolidated wires, ran a frame ground for front half of bike and frame ground for rear.

Changed fuse panel up for a single 10A inline and housed it in the bucket, and re-located ignition to a bracket off of the regulator.

Fired up and my lights are back, now going to wire a new harness when all the other colors arrive.

Happy days happy days.

 

[Bert Jan]

You mention the black/white is grounded. Thats bad. Black/white is live wire from ignition.