Hello Everyone. New to the forum and I need some help with a wiring issue. Not sure what to search to find out if it's been discussed before and I hope someone can point me in the right direction. I am building a 1977 CB750K basically from a junker. I swapped a 750F front triple tree and rear swing arm along with the Comstar wheels. It all came together nicely and I just finished up wiring yesterday. I started with a new harness and the only electrical upgrades are blade fuses, Dyna S electronic ignition and coils as well as the rectifier upgrade. I'll try and post some pictures of the bike later on. When I finished wiring and hooked up the battery, the lights came on even with the key in the off position. I actually unplugged the key switch and still had lights. I didn't blow any fuses and was able to test that everything was working properly. Needless to say, the battery drained in around 10 minutes while I was testing the signal lights and headlights and brake lights. Starter works too. Somewhere, I have a power line back feeding through the frame. I unplugged all of the lights and dash controls and still have the problem. I think maybe it is in the rectifier and charging system setup, but I haven't got that far yet. Can anyone help me with a place to start? My guess is that this isn't too uncommon of a mistake since most of the wiring was pretty straightforward and the harness wire colors matched the wiring diagram.
Wiring Problem
- Thread starter fatbob
- Start date
themotoworks
Been Around the Block
sounds like you have a keyed positive wire going straight to the battery, if everything works with the key unplugged
Maritime
Over 10,000 Posts
Did you buy the harness or make it? If it was a made in China deal they sometimes make mistakes and wire a connector wrong. If you made it yourself you may have missed a wire. the main power wire usually goes from Battery to RR then to key then out to all your accessories and coil etc. If the connections are mixed up you could have bypassed the key.
Maritime
Over 10,000 Posts
Is is a Spark Moto? If so Matt will help you figure it out. He's got great customer service. If ebay special you'll need to trace the power from the battery out to figure out where the issue is.
Maritime
Over 10,000 Posts
Nice work so far.
Maritime
Over 10,000 Posts
Just noticed the diagram I posted has a mistake, the top has Horn but it is you starter button. Also I don't know what the Starter motor safety switch is but it has direct power from the battery and Alternator so if miss wired or malfunctioning could be where your issue is.
I bought the harness from 4 into 1. Yes it is the upgraded regulator/ rectifier also from 4 into 1. That didn't come with any instructions. Does anyone have a diagram that is modified for this hook up? It was pretty straight forward to hook up, plug into the harness plug and I think 2 extra wires that matched color of the harness. I think this is most likely where the problem is. I unplugged and tested the lights and the brake switches last night. My plan was to dig into the wiring for the R/R tonight but I thought I would seek some advice form the experts that have also had to troubleshoot electrical issues.
Starter motor safety switch? I have a neutral switch and a clutch switch. Not sure about a starter motor safety switch. Come to think about it, when I turned over the starter to prime the oil pump, I had the bike in neutral, but the clutch safety wasn't wired yet. Starter still turned over though. You might be on to something there.
Maritime
Over 10,000 Posts
So the way the clutch and neutral switches work is, as long as one is on you're good. If in Neutral the starter is grounded. If not but clutch is pulled, starter is grounded. so not having the clutch hooked up didn't matter if you were in Neutral. A quick google brought up a bunch of SOHC threads about that ^^^ causing issues when re-wiring the CB's
Maritime
Over 10,000 Posts
I don't really see a difference on the diagrams. As for the safety switch:
http://forums.sohc4.net/index.php?topic=60528.0
https://www.dotheton.com/index.php?threads/what-can-i-get-rid-of.44246/
Basically it's the unit that tells the solenoid it's ok to run the starter. It's the reason you could start in neutral without the clutch pulled. There are much more modern easier ways to do that today.
http://forums.sohc4.net/index.php?topic=60528.0
https://www.dotheton.com/index.php?threads/what-can-i-get-rid-of.44246/
Basically it's the unit that tells the solenoid it's ok to run the starter. It's the reason you could start in neutral without the clutch pulled. There are much more modern easier ways to do that today.
Maritime
Over 10,000 Posts
Ok, on lunch here so I read some shit. Did you buy this: https://4into1.com/main-wiring-harness-32100-341-703-honda-cb750k-1973-1975/ or this https://4into1.com/main-wiring-harness-32100-410-010-honda-cb750f-1977-1978/
also there is a different diagram for the 77 CB750K7 late model.
http://manuals.sohc4.net/cb750k/technical_reference/WD750K7.pdf
it doesn't have the safety switch, it runs a Diode that if bad will allow the + all the time. so depending on the harness the wires may be routed wrong.
also there is a different diagram for the 77 CB750K7 late model.
http://manuals.sohc4.net/cb750k/technical_reference/WD750K7.pdf
it doesn't have the safety switch, it runs a Diode that if bad will allow the + all the time. so depending on the harness the wires may be routed wrong.
the one for the 1977/78. It has a diode and I assume the diode is working because the signal lights flash. I have the diode from the original harness that I can plug in to see and I think you can test with a multimeter. I will test the diode tonight. Thanks for so much information. I really appreciate the help getting me at least looking at the right things. The original harness was cut up nd had a bunch of custom circuits wired into it. It was helpful for some things and I labelled most of the connections when I took it off, but with all the splices, it was hard to figure everything out.
