Wiring loom

[Ian James]

Can anyone recommend a good loom for 73 Mk1 850? Australian?

 

[Dellis]

I’d just make your own. I did and got rid of loads of redundant wires, reduced the number of connectors and moved the switchgear connectors to inside the headlamp shell. It’s not a difficult job and is a bit improvement over the original especially under the tank where I now don’t have a great lump of bullet connectors.

 

[Ron L]

I’d just make your own. I did and got rid of loads of redundant wires, reduced the number of connectors and moved the switchgear connectors to inside the headlamp shell. It’s not a difficult job and is a bit improvement over the original especially under the tank where I now don’t have a great lump of bullet connectors.

But please do the next owner a favor and use the original wire color code. It is a pain in the rear to trace down a problem when a well meaning previous owner makes a nice compact harness with all black wire!

 

[ashman]

Make a wire diagram and a few different rolls of coloured wire, a good wire slicer, and a rachet crimping tool and decent connectors, its not a hard job to do and can get rid of so many useless wiring, I am lucky running a Joe Hunt maggie I have cut back 3/4 of my wiring on my bike, make it simple.
Not sure where you are in Aus but if you near Brissy I would like to help.

 

[texasSlick]

But please do the next owner a favor and use the original wire color code. It is a pain in the rear to trace down a problem when a well meaning previous owner makes a nice compact harness with all black wire!

If unable to use original wire color code, at the very least use a wire number at each end, and provide a wiring diagram marked with the wire numbers.

Note: all wires attached at a common point or terminal should have the same number, or color code. Wire numbers or colors do not change when passing through a passive device .... example, a junction block.

Use clear shrink tubing over the numbers to prevent flagging.

A nail board makes the job neat and easy.

Slick

 

[cash]

I rewired my Mk3 850 15 years ago using modern low resistance wire, connectors and separate fuses. I temporarily connected up everything that would be housed in the headlight shell just to check it would work, and it did. I bundled the rat's into and the shell somehow got the head light fitted. Then went for a test ride and everything worked as expected. It's still like that to this day. How time flies, one day perhaps I might tidy it up, but then again it'll give the one I pass it onto a nice surprise.
Oh! and by the way I'm 74 5ft 5" just over 10st, bad heart, got a gammy right knee and I've got the old lump starting so easily. I don't think I'll be refitting the starter anytime soon.
Thanks Jim Schmidt your cam/follower kit not only improved the motor's running but somehow has transformed it's starting.

 

[concours]

"using modern low resistance wire, "

Do tell, more about this new low resistance wire?!

 

[Jdub]

If making your own loom seems daunting let me tell you that not only will it be easier than you think, you will spend your money on tools you will retain, learn how your electrical system works, and ride free of the suspicion that the electrics will let you down. Plus everything mentioned in this post.

For me, I committed to Tri-Spark parts and adopted Greg Marsh's approach which can be seen here along with the excellent schematic you can see here courtesy of Grant Tiller. Take a few minutes to study this and consider the possibilities. Greg has updated his approach a bit, so a few changes, but overall you are setting a 14g red ground the length of the harness/motorcycle and tapping into that as your dedicated ground. From there, you are simply guiding wire from the various electrical devices into the harness and through to the headlamp, where all wires are joined and a very clean outcome.

PM me for more information if you would like. Total cost from British Wiring (great outfit) was about $250 but I have the tools and knowledge now and this price is about what you would pay for an over the shelf.

Zip ties color code your assembly - yellow indicates outbound wires:

The headlamp is the destination for your connections:

 

[Dellis]

But please do the next owner a favor and use the original wire color code. It is a pain in the rear to trace down a problem when a well meaning previous owner makes a nice compact harness with all black wire!

Well the next owner will be my son. But, yes I have been faithful to the original wiring colours and I have my wiring diagram saved in the bike’s history folder.

 

[marshg246]

But please do the next owner a favor and use the original wire color code. It is a pain in the rear to trace down a problem when a well meaning previous owner makes a nice compact harness with all black wire!

Anyone following my method is doing that! It's critically important to me as a large portion of the bikes I work on have terrible wiring. I no longer fix terrible wiring - I will re-wire or send you on you way. That's a new policy due to a guy with a 79 Bonneville that had every gadget you can put on a old bike - some I never knew existed. I wish he had used all black wire - he got an old harness and used whatever color for whatever.

Read just the first page and you'll understand: https://www.gregmarsh.com/MC/Norton/Norton_1974_Wiring.aspx

BTW, the "experts" like to complain that I don't add a bunch of fuses and so forth - the bike is wired the same, but with proper gage wire when the original is too small, and I detest the jumble of wires under the tank and all the extra bullet connections that causes. Since the frame is not a part of the ground on a Norton, I add a 14ga Red ground write from the headlight to the taillight and to keep from the stupid practice of running multiple 18ga red wires in a serpentine fashion, I splice into it where needed. I also run three white wires from the master switch: 1) One to the Left-hand switch console 2) One to the Right-hard switch console, and one to everything else. This ensures that the single white wire serpentine in the original harnesses is not overloaded. BTW, run with your headlights on and a standard horn, push the horn button and the wire is overloaded. If the horn is not sounding but intact when you push the button, it's possible to see smoke!

 

[johnm]

Anyone following my method is doing that! It's critically important to me as a large portion of the bikes I work on have terrible wiring. I no longer fix terrible wiring - I will re-wire or send you on you way. That's a new policy due to a guy with a 79 Bonneville that had every gadget you can put on a old bike - some I never knew existed. I wish he had used all black wire - he got an old harness and used whatever color for whatever.

Read just the first page and you'll understand: https://www.gregmarsh.com/MC/Norton/Norton_1974_Wiring.aspx

BTW, the "experts" like to complain that I don't add a bunch of fuses and so forth - the bike is wired the same, but with proper gage wire when the original is too small, and I detest the jumble of wires under the tank and all the extra bullet connections that causes. Since the frame is not a part of the ground on a Norton, I add a 14ga Red ground write from the headlight to the taillight and to keep from the stupid practice of running multiple 18ga red wires in a serpentine fashion, I splice into it where needed. I also run three white wires from the master switch: 1) One to the Left-hand switch console 2) One to the Right-hard switch console, and one to everything else. This ensures that the single white wire serpentine in the original harnesses is not overloaded. BTW, run with your headlights on and a standard horn, push the horn button and the wire is overloaded. If the horn is not sounding but intact when you push the button, it's possible to see smoke!

Yes I should really redo the wiring on my bike as you suggest. It's the only really dodgy thing left on the bike and I'm ashamed to look under the tank.

In my defence I did begin to instal a brand new loom with the unnecessary wires stripped out and the very first bullet connector I touched on the new harness pulled off in my hand. So I stuck that in the maybe box.

Next I decided to start from scratch including a horn relay. But I kept blowing fuses. After a long time I discovered the also brand new rectifier regulator was internally shorting to earth. It had been checked for problems but on a wooden bench so the short never showed up until I mounted it on the bike.

By this time I was so disgruntled that I simply patched up the harness that I had fitted about 25 years ago.

So still stuck with the junction mess under the tank. Maybe one winter I'll attack it again. I have all the correct coloured wires.

 

[Ian James]

Make a wire diagram and a few different rolls of coloured wire, a good wire slicer, and a rachet crimping tool and decent connectors, its not a hard job to do and can get rid of so many useless wiring, I am lucky running a Joe Hunt maggie I have cut back 3/4 of my wiring on my bike, make it simple.
Not sure where you are in Aus but if you near Brissy I would like to help.

Thanks Ash I'm at Coleambally f,ing miles away.

 

[seattle##gs]

For the main power wire from the key switch to the headlight toggle I use the thinwall 28 amp wire available from BRITISH WIRING here in the states. It is only slightly bigger than our 18 gauge yet carries 28 amps...more than enough capacity. Same with the red ground wire. For all the others I use the normal 18 gauge wire from the same source and it carries 8.75 amps
With no turn signals:
**I have one brown-blue wire from the key switch to the toggle
**one white wire to the ignition
**one brown-green wire from the headlight to the tail light. It makes a "T" in the battery area and the extra leg goes to the brake switch
**one red wire from the headlight to the battery are where it grounds to a bolt in the frame. All other grounds gather at this point. Then a single red wire goes from this point to the battery.

So the bulk of the wires is narrowed down to 4 wires going from the headlight area to the battery area. The headlight toggle switch distributes the 12V to the switches. The ignition wire (white) is separate from the main harness and dead ends under the tank where it plugs into the boyer. Grounding in that area (boyer, coils, cylinder head) is gathered at the frame coil and tank bracket. Then one red wire is spliced into the main harness ground.

I did an autopsy of a stock beaten up original wiring harness. I counted 19 red ground wires! And maybe 12 brown-blue wires if my memory is correct.
Throwing away the stock regulator-rectifier circuit and the points ignition wires elimates a ton of wires.

 

[Dellis]

For the main power wire from the key switch to the headlight toggle I use the thinwall 28 amp wire available from BRITISH WIRING here in the states. It is only slightly bigger than our 18 gauge yet carries 28 amps...more than enough capacity. Same with the red ground wire. For all the others I use the normal 18 gauge wire from the same source and it carries 8.75 amps
With no turn signals:
**I have one brown-blue wire from the key switch to the toggle
**one white wire to the ignition
**one brown-green wire from the headlight to the tail light. It makes a "T" in the battery area and the extra leg goes to the brake switch
**one red wire from the headlight to the battery are where it grounds to a bolt in the frame. All other grounds gather at this point. Then a single red wire goes from this point to the battery.

So the bulk of the wires is narrowed down to 4 wires going from the headlight area to the battery area. The headlight toggle switch distributes the 12V to the switches. The ignition wire (white) is separate from the main harness and dead ends under the tank where it plugs into the boyer. Grounding in that area (boyer, coils, cylinder head) is gathered at the frame coil and tank bracket. Then one red wire is spliced into the main harness ground.

I did an autopsy of a stock beaten up original wiring harness. I counted 19 red ground wires! And maybe 12 brown-blue wires if my memory is correct.
Throwing away the stock regulator-rectifier circuit and the points ignition wires elimates a ton of wires.

Agreed, if you do it yourself you get rid of quite a lot of wiring and more importantly a lot of connectors too.

 

[B+Bogus]

I do wonder how much money Norton 'saved' by using a single loom with all the Police siren wiring included on all their builds?
Unless I'm doing a 'correct' build, I replace all the connectors with Jap style bullets. The original connectors buried into chunky black junction blocks have been at the root of most of my electrical gremlins over the years - you have to yank on the wire to disconnect - if it does, and there's no strain relief when installed, so there's a fatigue point just where you can't see it.

 

[kommando]

I do wonder how much money Norton 'saved' by using a single loom with all the Police siren wiring included on all their builds?

Their chosen route was to build the Interplods down the standard production line and then to convert them in a separate department as each Police region/dept wanted different features. I don't think they wanted to go the same route as the Longbridge Show dept and put a guy from the Show dept in the body as it dropped on the assembly line and then get him to tell every operator to either fit or leave off the parts he normally fitted, so having a common harness reduced the stripdown required in the conversion. Whether it made £ sense really depended on how many Interplods were made.

 

[L.A.B.]

Most Interpol wires were additional, only short sections were included in the standard harness.

Police siren

Alternating horns.

The 850 Mk3 harness had no Interpol wires.

 

[Ian James]

Can anyone recommend a good loom for 73 Mk1 850? Australian?

Thanks for the replies. I will make my own.

 

[joe czech]

if it's not too late to add to the conversation, on my 74 Mk2, i installed a lucas servive replacement harness. for the most part, plug and play, i did a slight mod for the tri-spark, but other than that, no issues.

side note - i used this contact grease on all bullet connections. about 4 years now, not one harness related electrical issue.

 

[ashman]

Did you get a tin of Lucas smoke as well.