Author Topic: Blue/red wire off harness (Read 911 times)

mr.brandon · « **on:** April 23, 2022, 09:54:46 PM »

Hello gang, I had a bad accident awhile back and am now rebuilding my bike. I have a 1974 k model and am trying to find out what the blue/red wire is in the harness? I believe the light green/red is oil pressure, but not sure? Also..I have a black thick gauge (battery cable) from starter motor... does that connect to ground (-12v to battery) or (+12vside) side of solenoid? Is that the ONLY wire to hook up for starter motor? (The green/red (on starter side, under case) gets grounded? Sorry, lots of questions... I REALLY can use the help!

bryanj · « **Reply #1 on:** April 24, 2022, 03:24:01 AM »

What you need is the wiring diagram for that year/model which i dont have as it never came to UK.
Big wire from starter goes to solenoid, it grounds via the casing and frame.
Green/red wire varies by year
Blue/red could be EITHER power feed for headlamp fuse OR indicator buzzer as i understand it depending on exact year/model

69cb750 · « **Reply #2 on:** April 24, 2022, 03:41:25 AM »

Blue/red is oil pressure switch
Green/red is neutral switch

mr.brandon · « **Reply #3 on:** April 24, 2022, 07:52:13 AM »

Thank you... so I really could just cap off both green/red and blue/red from harness and not connect,ground, etc. If I am using a bobber frame and running both headlights off of a toggle (+12v) to (-12v) from other headlight connect?there is just the one ground for the starter not a (+12v) line?

TwoTired · « **Reply #4 on:** April 24, 2022, 07:57:22 AM »

You might look at reply #9 in the electric FAQ for wire color/ function guides.

mr.brandon · « **Reply #5 on:** April 24, 2022, 08:19:22 AM »

Or... if I use both wires,.. hook both to (+12v)?

mr.brandon · « **Reply #6 on:** April 24, 2022, 08:29:50 AM »

I have no yellow/red wire (that I can see) is that the 12v+ for the starter motor (won't work without it?)

Don R · « **Reply #7 on:** April 24, 2022, 10:41:55 AM »

http://oldmanhonda.com/MC/WiringDiagrams/CB750(K3-K7).jpg

Don R · « **Reply #8 on:** April 24, 2022, 10:46:34 AM »

You have a starter safety unit that complicates things a bit. Your start button makes the ground that completes a circuit to energize the start relay. The relay gets 12V from the other wire in that pair at the unit.

mr.brandon · « **Reply #9 on:** April 24, 2022, 10:57:59 AM »

What other wire (color) the big black battery cable from the starter motor?

69cb750 · « **Reply #10 on:** April 27, 2022, 11:11:31 AM »

The oil switch provides ground when engine not running, the other wire to the light has +12 volts when ignition is on.
The neutral switch provides ground when in neutral, the other wire to the light has +12 volts when ignition is on.

mr.brandon · « **Reply #11 on:** May 03, 2022, 09:33:21 AM »

What other wire (color) to what light?I DO NOT have a stock '74 cb750k, only the engine in a bobber frame. I ran +12v to the solenoid (from batt.) Ran the big black battery. Cable from starter motor to -post on solenoid and another -12v from that post to -12 on battery then grounded another wire from -12v on battery to frame. The green/red from solenoid goes to push button start button and the other line off that "push" button goes to -12v on battery, the yellow/red off of solenoid gets grounded. Then +12v goes to the (grounded) oil pressure wire (with a light in between the +12v terminal on battery. And the connection at the harness) does that ALL sound to be correct?

Don R · « **Reply #12 on:** May 03, 2022, 02:05:59 PM »

No.
It sounds like you have the - negative side of the battery connected to the solenoid. There should be only + from the battery to the solenoid and the feed to the starter. A small red wire connected on the battery side of the solenoid feeds the fuse panel.

- on the battery, only goes to the frame/engine bolt or a green (honda color) chassis ground.

Any DC electrical device (load) needs positive on one side and negative on the other.

Don R · « **Reply #13 on:** May 03, 2022, 02:09:54 PM »

http://www.hondachopper.com/garage/simple_wiring_diagram/simple_wiring_diagram.html

mr.brandon · « **Reply #14 on:** May 03, 2022, 11:02:09 PM »

Hilarious, i pretty clearly don't know what I am doing so... I am trying to learn and look to those with knowledge for help.you instill fear in my heart but give absolutely no direction. Thank you.

mr.brandon · « **Reply #15 on:** May 03, 2022, 11:15:32 PM »

Thank you Don R., you have been a TREMENDOUS help to me and it is extremely appreciated. I believe I have it all wired except for the blue/red(oil pressure) which is grounded at the starter..I will hook +12v to it w/ a light in the middle. I believe that is correct? What I am kinda wondering about is the VERY light green/red (neutral switch) it comes out above and below the starter motor housing.Below, I believe gets grounded on the motor...Above (at harness) I "think" either hook to +12volt or...cap off?I don't know about this one.im not sure about the blue/red either but REALLY don't know about the neutral (how to connect it on both sides although, as I said, I think it gets grounded on the side that is below the housing).I could probably use help on both though?

robvangulik · « **Reply #16 on:** May 04, 2022, 05:45:21 AM »

The neutral light has a permanent connection to a hot plus wire, and the other wire end is connected to the neutral switch on the engine, which completes the circuit to ground/engine when in neutral.

Don R · « **Reply #17 on:** May 04, 2022, 03:17:29 PM »

The neutral switch is located on the bottom of the engine, the wire goes up from the bottom, through the sprocket cover into the harness and comes out in the headlight bucket where it goes to the Neutral
indicator light, the other wire from the bulb wire gets 12V+ from a black feed in the headlight bucket. Black is hot when the key is on.
It's the same idea as the oil pressure switch/ light.

mr.brandon · « **Reply #18 on:** May 05, 2022, 05:18:13 PM »

So... I had a hanging neutral switch wire which I though was supposed to be grounded on the engine(which is what I did) coming out of the sprocket cover it ends at the harness.i don't have a stock headlamp w/all the birds nest of wire, I have only 7 out of the harness..1)if I cap off the neutral switch wire but leave it grounded will the bike still start and run? Or... 2)if i connect a bulb to it (out of harness) and on other side of bulb hook it to a spliced regulator black, will that work3)same as 2 but instead of splicing the black, run from the bulb a line to "ignition"(which will be hot when key is on).will any or all of those work?the oil pressure I will hook a bulb out of harness and on other side +12volts.this should answer all questions for my project. Thank you all with a very special thank you to Don, you have REALLY helped me man!

mr.brandon · « **Reply #19 on:** May 06, 2022, 11:20:02 AM »

Alright perfect. I don't have a horn but, the harness does have black... I will splice the black to both wires or run to my ignition on my key switch which should be the same as black (hot) when bike is running. Thank you much

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Author Topic: Blue/red wire off harness (Read 911 times)