Topic: Any wiring specialist ? electrical break down CB 750 K2

[aminemed]

when key is turned twice it is on park. I believe that all motorcycle lights should be on. Ignition not possible though

[HondaMan]

when key is turned twice it is on park. I believe that all motorcycle lights should be on. Ignition not possible though

When the key is turned 2 times to PARK, the rear taillight comes on and the little Brown wire in the headlight bucket receives power, too. In Europe, when this bike was produced, several countries required there also be a small pilot light in the headlight, which turned ON with this key position. It was to be turned ON whenever the bike was parked in certain metropolitan areas, to limit the time it could remain.

[aminemed]

Here is where i stand today, run a few wire test:

Ignition switch:

Only red wire is +12v. Black wire with key turned on position 1 doesn't display any voltage.

Headlight bucket:

Blue wire: ok +12v
White wire: ok +12v
All black wires: +12v

I noticed that there is a female brown wire without a male wire, don't understand...

yet, there is not light

Rear stop:
Brown wire: no voltage
Red and yellow: +12v

rear stop is working only when key is on position 2 (park).

Fuse box:
It is in a bad shape but managed to make it work by cleaning it a bit

Starter solenoid
red wire: +12v
black wire: there is a black wire going from the starter relay and i guess this the black wire that goes to the key switch. Is it supposed to be @ 12v when key is on ?

any clue on that ?

[aminemed]

yes i do blk and white is ok ! what I don't understand is that I have 12v in the headlight bucket ! blue and white are both displaying 12v (without having any light though) and other black wires are 12v as well

[Mr. Mike]

12 volts on blue and white in the headlight?
Wow, I thought the 12volts was switched to blue OR white depending on the switch position. Seems there is trouble at the keyed ignition  switch (coils and lighting) as well as the hi/low beam slide switch (hi and low beam wires showing 12volts). All this from hooking up the module incorrectly. Guess you were right when you said it all went "boom".

[HondaMan]

Hmmm...check that main ground? On the 750, this is a Green wire at either the front coil brackets' mount, with a CLEAN bare spot under it, at the frame, or else it is underneath the seat, on the seat-lock bracket (also must be cleaned periodically).

[Spanner 1]

Fuse box 'in bad shape' is not gonna do it !, also are the battery terminals shiny and the ring terminals on the + and - wires. Must be shiny, not just clean 

[Spanner 1]

It's common to measure 12v in a circuit with no load and then to measure 0v when the load is applied = #$%*ty battery connections/ground / fuse box

[aminemed]

I finally know what was going on. It's so stupid that i hope to not be banned from this forum

My main ground wire was the cause. I fixed it and now all my lights are back.

Bad news is (and need your opinion on that), my lithium battery is damaged. Motogadget was warning that reversing polarity can damage battery, so that's true.

I plugged it to a charger and measured its voltage: +13v, but when i plug it to my bike, i do not have enough power to start the bike. Battery voltage drops under 10v when i measure it just afterwards.

[540nova]

I was going to suggest you thoroughly check all grounds, but you had plenty of advise thrown out, already.
Glad you got it sorted out.

Sent from my SM-G955U using Tapatalk

[aminemed]

before throwing another 150 bucks to buy a brand new lithium battery, i just wanna do a sanity check:

is there anything that can drain a fully recharged battery just when trying to start the bike. I fully charged my battery with, voltage is higher than 13 volts. As said before in my other posts, my battery was displaying a voltage higher than 13 volts until i tried to crank the bike.

I measured its voltage these last two days after a full recharge, voltage was stable around 13.5 v. Any bike start attempt would drop its voltage to 9.8 volts and with this voltage, bike do not want to start.

I'm then wondering if there is anything i'm missing here, any wire, etc, that can cause my battery to loose its voltage. thnx for your input

[540nova]

Absolutely.  These bikes are notorious for that, if it doesn't start after just a few attempts. You're better off kicking it until it's in tune well enough to fire up instantly.

Sent from my SM-G955U using Tapatalk

[aminemed]

Just to add a small precision, when fully charged battery is at 13v, not only after its full charge, but it remains at this voltage without any drop, that's why I'm wondering if anything is going on in the bike itself

[Keith]

Yep....bad ground is my guess, a simple voltage drop test will find this in a few minutes. Everyone shoud learn this essential test.

[Spanner 1]

It's common to measure 12v in a circuit with no load and then to measure 0v when the load is applied = #$%*ty battery connections/ground / fuse box

Yes, if the circuit had both a POS and a NEG connection. But the statements were “bad fuse block” and “poor ground”. If these were the cause, then there wouldn’t be a reliable voltage measured the other side of the circuit. Capisci?!

What ?.... with the Black meter lead on the battery Neg. and the Red lead on the red to the ign. switch and you read 12v, then turn the ign. 'on' and voltage drops to 0, proof of #$%*ty battery connection or #$%*ty main ground ( as OP confirmed today ).

[aminemed]

13.0v is not fully charged for most lithium batteries. As said before, they don’t tolerate being over-discharged. If it drops to <10v when turning the key ON, you’re toast.

not when turning key on, it remains above 13v in this case. It drops to 9.8 volts when I hit the electric start. Engine cranks without firing up

Then I believe as well that if the battery is completely toasted it wouldn't go up to 13.7 volts when i charge it. Guess so..

[aminemed]

13.6 volts (that's the voltage of my battery). When key on, battery voltage does not drop.

[aminemed]

13.6 volts (that's the voltage of my battery). When key on, battery voltage does not drop.

Thanks. That is not the impression I had from your prior posts.

battery voltage drops when i press start button, engine cranks then battery is around 9.88 volts all of the sudden

[aminemed]

lithium lifepo4 battery, 12v 4.6ah. Was working greatly, one pressure on starter and bike fired up.

[aminemed]

240 A

[nuwonder]

Would be good to do a quick test with another (good) battery, if you can get a spare cheap. Perhaps the old battery is still ok after charging?

Also, is your engine grounding properly with the frame? I had all kinds of electrical trouble back in the day because I overlooked this.

[aminemed]

i'm going to jump start the bike with my car battery

[aminemed]

Ok sorry made a mistake and took a wrong value from my meter.

I took my meter again and this time measured correctly:

Voltage battery, bike off: 13.69 volt

Key on and kill switch OFF: battery voltage starts dropping, almost 0.1 volt / sec, i turned the key off and battery voltage remained at 12.7 (and did not revert back to 13.6 volt..)

With kill switch ON: worst..battery drops quickly at 12 volts and lower

I took off battery and connected it to my wall charger until voltage was around 13.6. This time, i disconnected my tail light wires (don't know why i did it, seemed to me that i was doing something as a pro). Anyways, same phenomenon, but this time i quickly pressed the elec start and bike started for a few seconds..(did not start for 3 weeks now).

Battery is now at 12.47