Topic: New Wiring Harness Recommended?

[Popwood]

I’ve had off and on electrical issues with my 1975 K5 750. Currently struggling with battery not charging problem. I’ve put about 10K miles on it since bought used and the few problems I’ve had are all wiring related. I’ve done all maintenance on this bike and my ‘75 550 over the past 15 years so I’m not too concerned about digging into this project. So now that she’s about to turn 50, I’m thinking about a new wiring harness. Over the years I’ve found melted wire insulation, unexplained wires here and there, some just spliced in and a tangled mess in the headlight bucked where wires from a Windjammer fairing tapped into lighting not done very well.

Is a new wiring harness in order? Or is that just wishful thinking hobgoblins will magically disappear? And if a new main harness is in order, recommendations on where to buy? And if I do, what other electrical issues should I be prepared to address? Like the the things that plug into the main harness?
 
Thanks for your input.

I’ll be most grateful for advice

[Alan F.]

https://vintagecb750.com/collections/electrical/products/wire-harness-24-4001

[Popwood]

Can I assume the link is to a harness you recommend? Do you have experience using one? Thanks.

[BenelliSEI]

I’ve used a few of their harnesses. Make sure you order the one for your bike. They have been great for me. I recall one (I think it was for a ‘75 cb750F) that had a wire colour that was a different shade, but once sorted it worked out fine.

Most recently I installed one on a cb750K0 and it worked perfectly.

[CycleRanger]

A new harness is cheap compared to the hassle of an old, brittle, damaged harness.

[scottly]

Currently struggling with battery not charging problem.

Like the the things that plug into the main harness?
 

The problem you had with the neutral and oil pressure lights was caused by a lose connector plug. Was there a white, a green, and three yellow wires in that same plug? Those are the wires that go to the field coil and stator of the charging system. I would take a close look at that plug before replacing the main harness, as far as the charging problem.
BTW, the rat's nest in the headlight bucket is normal.    

[Alan F.]

Can I assume the link is to a harness you recommend? Do you have experience using one? Thanks.

Yes, you would be correct to think that, Sir.

Their reproduction harnesses heve been recommended to me by several members in recent years. I have bought other items from this vendor before and their general quality is high. I have a K8 harness in transit and will be ordering this K3 harness soon.

[pjlogue]

I agree with CycleRanger and a new harness is a good idea.  If you go the new harness route I would also recommend replacing the plug and metal connectors to the alternator.  These get corroded over time and the resistance in the connector goes up and will melt the plastic connector.  I would also invest in a bullet connector kit and crimper and replace any connectors from the handle bar controls that are inside the headlight bucket that are in bad shape.  Clean all connectors that can be reused with 0000 steel wool and apply Dielectric grease to ALL connectors when you put in the new harness.   I would also invest in a good multimeter and wiring diagram before you begin.  I would also recommend pulling the 3 fuses in the fuse block, clean the contacts in the block and replace the old fuses with new ones. 

This is what I have done for my '76 750K and '76 GL1000 and I have had absolutely no problems with either bike since their restorations.  The only problem I had while doing the wiring is the new harness may not have the exact color wires the original harness had.  New harness may have shrink rings at the connector that match the color (or close to it) instead of the color stripe on the original harness wire.

-P.

[MRieck]

A new harness is cheap compared to the hassle of an old, brittle, damaged harness.

You can say that again. Wiring harnesses are made to be replaced especially after 50 years.

[MauiK3]

You can also check Yamiya, good products. I used one of theirs on my K3 750.

[rocket johnny]

don't forget to order the harness for the dashboard .  it is not included with the main harness .  after replacing the main harness on my 76 k-6 all was good for a few years then i would blow the main 15 amp fuse .  it turned out to be the rubber boots around the bulbs on the dashboard were rotten and shorting out .  replaced that and life has been good so far ,,,

[Kelly E]

For hard to clean connectors I hold the connector in a rag and spray into it with battery terminal cleaner. After the cleaner foams up rinse it out with non-clorinated brake cleaner and dry it out with the air nozzle. After drying I inject dielectric grease into the female half of the connection and assemble. When I resurrect a bike or a car I clean every connector with this method. I have had excellent results doing this. I even got everything electrical in my 72' MGB GT working.

[Jerry Rxman Griffin aka MuthaF'er]

I FINALLY replaced every piece of my harnesses that I could find plus the ignition lock set. FINALLY haha no more charging issues

[Popwood]

Currently struggling with battery not charging problem.

Like the the things that plug into the main harness?
 

The problem you had with the neutral and oil pressure lights was caused by a lose connector plug. Was there a white, a green, and three yellow wires in that same plug? Those are the wires that go to the field coil and stator of the charging system. I would take a close look at that plug before replacing the main harness, as far as the charging problem.
BTW, the rat's nest in the headlight bucket is normal.    

Scottly, took a closer look at that plug and you nailed it! three yellow, white and green. Also think I saw a red white. It was properly plugged together  but also looked quite dirty. I’ll clean the contacts thoroughly. Clearly, the yellows white and green are running between the field coil and stator to the rectifirer, yes? After cleaning I’ll see if battery is charging while running engine at 4000 rpm or more.

[scottly]

White field coil wire goes to the regulator, green field coil wire goes to ground, and three yellows go to the rectifier. After cleaning, try the field magnetism test again.

[Popwood]

All good! Cleaned that multi-wire plug best I could (how do you clean the female side, such a tiny opening?), gooped up with dielectric grease, put the battery back in, turned system on. Encouraged when bolts clung to the three screws fastening on the alternator cover. Feeling good. Put tank back on and fired her up. Multi-meter read up to 14.7 volts on battery poles with engine revving at 4000.

Thank you all sooo much, you da best!!!