1975 Mk III wiring

Needed my Mk III rewired. I have made this statement before" I can rewire but it looks like Gene did it!" I contacted Greg Marsh about doing it and he agreed. He has many improvements and eliminated all the none essential wiring. All connectors are inside the headlight housing and MUCH better quality then originals. What a professional job! Most if not all information on this job is on his web sight. Thanks again Greg!

That is a very clean looking wiring job.
I'll wait for wireless technology before I do this MkIV.

Interesting location for that oil pressure switch.
Nice clean harness Greg.

Deets55 said:

Interesting location for that oil pressure switch.
Nice clean harness Greg.

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That oil pressure switch confused me at first. It's Don Pender's and I sold it to @mean gene, but it was straight when I did. Gene, cut, welded, and cleaned it up to where it looks like it was made that way!

I like the location, but it wouldn't work there without Gene's mod.

When Don came out with the switch, I was in the middle of developing one as I always missed it on Nortons (Triumphs have them), and mine was going to mount there but on the other side. I don't believe in even the appearance of stealing someone else's idea, so I contacted Don and started using/selling his and still do.

For those that are interested wiring their MK3 "my way", I modified my pre-MK3 schematic done by Grant Tiller and then he made a MK3 version. It is linked near the end of my write-up: https://gregmarsh.com/MC/Norton/Norton_1975_Wiring.aspx

BTW, the console is what I'm proudest of. Gene's was in terrible condition and buying all the parts to restore it was going to cost much more than making it trouble-free and much nicer looking IMHO. The warning lights do look different (IMHO, much better), but are not plastic, are waterproof, are LEDs, and retail for $7.99 each on Amazon and cost even less when bought from the manufacturer. https://a.co/d/11A2jzP

I really liked this project - I've wired lots of pre-MK3s but this was the first MK3. The MK3 has MANY more wires than the earlier bikes and I was initially concerned that "my way" which makes most connections in the headlight shell might not work. As it turns out, figuring that out makes plenty of room in the headlight and I'll use those methods on all going forward.

That bike is so clean! It makes it a joy to work on I'm sure. Mine has years of road dinge all over everything one can't wash with the bike assembled.

How much of that extraneous wiring was for Interpol applications? Not that it matters but I'm curious, having worked on the wiring on many of these in the past.

I spent a morning last week reverting my MKIII wiring back to factory, cutting out several connectors I had installed for running lights and a frame-mount fairing I'll never use again. Didn't weigh much but there was a bit of a bird's nest lying on the floor when I was done.

I also re-wired the Canadian headlight assimilator that I'd wired around years ago when it failed. None was available then. If you ride in traffic this is a worthy little device. With the ignition switch in first position the head and tail lights are isolated from the battery and run solely off the alternator so they can't discharge the battery. In second position the lights work normally but can run the battery down sitting in traffic. I don't recall just now if the wiring harness is unique to Canadian models; which mine is.

By the MKIII days Norton had upgraded many of the connectors but sadly not many of those exposed to weather. Some in the headlight shell are better, some not. Ironically, one of the non-bullet type was corroded on mine in the front-stop-light circuit; hadn't worked in years. I'd be interested to know what connectors Greg uses. Can't see from the photos.

On a from-scratch project I did on a 650SS restoration years ago I used brass bullet connectors, both male and female and marine switches with rubber boots. I think I got them all from the marine equipment supplier in town. Non-factory but the owner was pleased.

Thomasa said:

How much of that extraneous wiring was for Interpol applications?

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There are no Interpol wires in the Mk3 harness.

Did Interpol buy no MKIIIs?

Having now looked at Greg's web blog and photos I'm even more impressed at the quality of workmanship. This level of quality takes hours and hours. And not just the hand's-on part. Researching supplies and sources is it's own project.

I need to have Greg rewire the sins I've committed under the dashboard of my AD ('51) Chev pickup. I've taken too many shortcuts (old wires abandoned in place and worse) because I can't physically work under the dash anymore. I can stand next to a bike on the lift however.

Thomasa said:

Did Interpol buy no MKIIIs?

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Were there Mk3 Interpols, yes.

L.A.B., Did Interpol provide their own wiring harness for police accessories? I know MKIIIs could have 3-phase alternators. I have such a kit, though bought aftermarket with a factory part number.

Greg, If there is a next time for MKIII wiring, and I have no reason to assume there won't be, I have a couple of suggestions:
1) Wire the kill switch in such a way that it defeats the ballast-resistor bypass so one can crank the engine with no ignition power ( bypass is of course unneeded on electronic ignitions). I've found that just a few strokes frees up the engine is enough that the starter's torque limiter doesn't release with alarming noises. With my bad hip I don't like kicking them at all.
2) Wire an ignition-kill circuit to the oil pressure switch to kill the ignition if oil pressure is lost. This, of course would require it's own override for starting purposes. I think that could be done in conjunction with the ballast bypass so it would be automatic but that would defeat #1. I have such a circuit on my truck to shut down the electric fuel pump AND shut off the ignition in the case of oil pressure loss. Over the years I've seen several total oil loss events from fractured oil lines and cracked oil tanks on Nortons, and class 8 trucks in which case it was very, very expensive.

I have done #1 on my MKIII but not #2 as I don't have an OP switch. That's a next project.

Thomasa said:

Did Interpol provide their own wiring harness for police accessories?

Click to expand...

Interpol is the model name sold to police and military, I doubt Interpol actually bought any. Yes the Mk3 Interpol wiring seems to have been additional.

Thomasa said:

I know MKIIIs could have 3-phase alternators.

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Generally the RM23 single phase.

Thomasa said:

That bike is so clean! It makes it a joy to work on I'm sure. Mine has years of road dinge all over everything one can't wash with the bike assembled.

How much of that extraneous wiring was for Interpol applications? Not that it matters but I'm curious, having worked on the wiring on many of these in the past.

I spent a morning last week reverting my MKIII wiring back to factory, cutting out several connectors I had installed for running lights and a frame-mount fairing I'll never use again. Didn't weigh much but there was a bit of a bird's nest lying on the floor when I was done.

I also re-wired the Canadian headlight assimilator that I'd wired around years ago when it failed. None was available then. If you ride in traffic this is a worthy little device. With the ignition switch in first position the head and tail lights are isolated from the battery and run solely off the alternator so they can't discharge the battery. In second position the lights work normally but can run the battery down sitting in traffic. I don't recall just now if the wiring harness is unique to Canadian models; which mine is.

By the MKIII days Norton had upgraded many of the connectors but sadly not many of those exposed to weather. Some in the headlight shell are better, some not. Ironically, one of the non-bullet type was corroded on mine in the front-stop-light circuit; hadn't worked in years. I'd be interested to know what connectors Greg uses. Can't see from the photos.

On a from-scratch project I did on a 650SS restoration years ago I used brass bullet connectors, both male and female and marine switches with rubber boots. I think I got them all from the marine equipment supplier in town. Non-factory but the owner was pleased.

Click to expand...

Don't know of any specific Interpol wires. Eliminating the points, rectifier, Zener(s), Assimilator, Capacitor, and under tank connections greatly reduces the connections and removes a bunch of wiring. The only added components in this MK3 are the oil pressure switch (no additional wires needed as the red warning light that was for the assimulator is used), and two diodes to make an LED turn signal warning light usable. Using a Tri-Spark ignition also reduces connections over the EIs.

I have until now always used Lucas-type bullets from BritishWiring.com. They are superior to the originals. There was no way that those connectors would work in the MK3 headlight as there are many more wires and bullets are inline which makes routing require longer wires. So, almost all in-headlight connections are WAGO 221 Lever connectors. Since used in a motorcycle, although not required, each bare wire was not touched by my fingers, and each was dipped in Permatex Dielectric grease then the excess wiped off with a clean blue towel. There should never be a bad connection with them, but if there is it's very easy to replace the connector, they have a built-in test port, and they cost less than bullets and connectors. All connections outside the headlight are new bullets and connectors as these are usually better being inline connectors (for instance in the taillight). The only spade connectors used are the front and rear brake switches. Ring terminals are used on the coils and the coil terminals were well cleaned with a brass brush and the covered in dielectric grease so the common problem cause by spade terminals there won't occur.

BTW, I was going to use Molex "Mini-Fit Junior" connectors which are similar to the originals, but they are max 18ga AWG and the correct wire is a slightly greater OD, much more expensive, a much greater PITA, and take up way more space.

Thomasa said:

L.A.B., Did Interpol provide their own wiring harness for police accessories? I know MKIIIs could have 3-phase alternators. I have such a kit, though bought aftermarket with a factory part number.

Greg, If there is a next time for MKIII wiring, and I have no reason to assume there won't be, I have a couple of suggestions:
1) Wire the kill switch in such a way that it defeats the ballast-resistor bypass so one can crank the engine with no ignition power ( bypass is of course unneeded on electronic ignitions). I've found that just a few strokes frees up the engine is enough that the starter's torque limiter doesn't release with alarming noises. With my bad hip I don't like kicking them at all.
2) Wire an ignition-kill circuit to the oil pressure switch to kill the ignition if oil pressure is lost. This, of course would require it's own override for starting purposes. I think that could be done in conjunction with the ballast bypass so it would be automatic but that would defeat #1. I have such a circuit on my truck to shut down the electric fuel pump AND shut off the ignition in the case of oil pressure loss. Over the years I've seen several total oil loss events from fractured oil lines and cracked oil tanks on Nortons, and class 8 trucks in which case it was very, very expensive.

I have done #1 on my MKIII but not #2 as I don't have an OP switch. That's a next project.

Click to expand...

There is no ballast resistor so no bypass and Tri-Spark will work down to 8.5 volts so none is needed. Yes, I know that the coils are boosted with the bypass but it's not used with any EI I'm aware of since there's no way to boost - they are like a single 12-volt coil and there's no boost room.

The kill switch provides power to the EI. The oil pressure switch has one side grounded - when there is pressure there is no circuit. What you suggest would require a relay (mechanical or electronic) that reversed that logic. That would be cool except.... Hot day, sitting at a light at idle, the oil pressure switch is on the edge and often flickers the warning light - read as shuts off the engine if I used it like you say so a bunch more electronics would be required to get around that and that would slow response time if you lost pressure. The oil pressure switch is not a high precision device - below 4psi it is surely closed, above about 7psi it is surely open in between it is in entropy. Sounds bad, but then an oil pressure gauge will likely read zero at that time and scare the crap out of you! At least a flickering light tells you there is some pressure, and that the light is good.