Couple of MkIII wiring questions

On the hopefully last lap of my "make it run" mystery bike rebuild. Have looked at several wiring diagrams but going to ask to be sure...

This is a positive ground set up with a Boyer ignition.

1. Is it OK to put the coil ground (red wire) directly on the positive battery terminal or should it be grounded to the chassis?

2. Does the Brown/Green wire with the fuse holder connect to the negative battery terminal?

3. Am running the original Lucas headlight. There are two positive ground lugs (one on the headlight shell and on the bulb retaining cap). Where does the red wire (has heat shrink coming from the main wiring harness) and the red stub wire from the pilot light go?

4. In the headlight shell there is an extra nylon connector block with brown and white wires that has no apparent match. Am I missing something?

Many thanks... Want to get this hooked up to see if I have spark and/or other unforeseen problems.

Andy

I just went through this on a MK3, so I think I can answer some of the questions.

Regarding question #2, yes, the brown/blue wire lug goes directly to the negative battery terminal.

For #3, both red wires, one from the bulb and the other from the wiring harness (return for the tach, speedo, and pilot light bulbs) are grounded to the headlamp shell. If memory serves me correctly (and it doesn't always), they should both have bullets on the end and plug into the single ground lug on the shell, one from each side.

For #4, the only brown and white wires I know of at the front are the ones that go to the front brake light switch. The brown and white wires from the front master cylinder switch are in a short harness that goes from the master cylinder switch to the plastic connector you are referring to (I think).

Not sure about #1. Are you referring to the red wire that grounds the coil bracket to the engine, or to a red Boyer wire?

Ken

Thanks Ken -

Very helpful..

On #1 the red wire in question is running from the left side coil into the battery box. Already have a red wire spaded to the head steady from the main harness grounded to the engine. The Boyer instructions simply say earth/chassis ground.

Your comment made me realize that the spare brown/white connector is indeed for the front brake light switch.

Saw your ultimate Norton build also. Very nice..

Thanks again,

Andy

ag12680 said:

1. Is it OK to put the coil ground (red wire) directly on the positive battery terminal or should it be grounded to the chassis?

Click to expand...

If you have a working starter motor you could connect the coil 'ground' directly to battery positive but only if it does not have an additional connection to any other harness retun (red) wire and/or chassis point.

ag12680 said:

2. Does the Brown/Green wire with the fuse holder connect to the negative battery terminal?

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Brown/blue.

ag12680 said:

3. Am running the original Lucas headlight. There are two positive ground lugs (one on the headlight shell and on the bulb retaining cap). Where does the red wire (has heat shrink coming from the main wiring harness) and the red stub wire from the pilot light go?

Click to expand...

Both should be connected to the harness return (red) and not just the headlamp shell. The headlamp shell 'ground' is a return for the front indicators/blinkers to connect to the harness return, it is not a headlamp ground.

The shell ground can be used as a junction point as long as there is a connection to the harness return (red).

I'd also strongly advise against connecting any harness return (red) wires directly to battery positive when a starter motor is operational, as given the right set of circumstances, it is possible for the starter motor current (100A+) to attempt to return to the battery through the harness wiring! If that happens, then the return wiring will burn out as it is not protected by the main fuse!

ag12680 said:

Click to expand...

(Those starter motor/battery cables would probably benefit from an increase in gauge)

http://atlanticgreen.com/cables.htm

LAB

It has a working starter that I will upgrade once I get it running. Kick start only for now...

The heavier gauge red cable terminates on the engine case half bolt. The harness also grounds to the engine at the head steady. Not trying to do anything other than return to stock configuration including the Boyer.

Based on what you're saying, I believe the engine, coils (connected separately to the Boyer) and battery are OK to share a common ground?

Andy

ag12680 said:

Based on what you're saying, I believe the engine, coils (connected separately to the Boyer) and battery are OK to share a common ground?

Click to expand...

Without an operational electric starter, the harness or any other return wiring can safely be connected directly to battery(+).

With an operational electric starter, it is safer to arrange the harness 'ground' wiring so all grounds are directed toward the engine and must ultimately make the return through the heavy gauge positive cable. This prevents any chance of the harness wiring burning out due to starter current passing through the harness return wiring.

The secondary battery "earth"/ground (as shown on the MkIII wiring diagram) is an electrical error, it shouldn't be there whenever a starter motor is part of the electrical system.

I use a coil bracket bolt as the main ground connection point, and run a wire from there to the 'engine'.

Well, the good news is that the bike started on the 3rd kick..

The bad news is that I can't get it road legal until solving the the headlight issue with the following clues:

1. The switchgear and ignition have been checked.
2. The 10 amp fuse blows on the blue/white headlight wire
3. The pilot light is always on.
4. The position of the L/R switchgear has no effect on the head/pilot lights.
5. All the main harness connections have been checked.
6. There is no apparent chafing/damage to the harness.
7. Turn signals and brake/park lights work.
8. Bike starts and runs fine.

Have the wiring diagram from the MkIII online PDF and nearly cross eyed from studying it. Is there a better one?

Appreciate any insights. Have a meter and trying to ring out the harness as best I can.

Fred at Oldbritts told me this is why he just makes his own.. Really don't want to do that...
Andy --

ag12680 said:

2. The 10 amp fuse blows on the blue/white headlight wire

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There must be a short somewhere in that line, or, perhaps in the bulb holder?

ag12680 said:

3. The pilot light is always on.

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As in, "on when the ignition is OFF", ....or?

ag12680 said:

4. The position of the L/R switchgear has no effect on the head/pilot lights.

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The right-hand cluster sliding switch turns the main headlamp ON or OFF (so selects either 'headlamp and pilot' or 'pilot' only). All other lighting (including the pilot) is powered from the ignition switch, terminal 3.

Power to the RH headlamp selector switch should come from a blue/yellow [UY] connected to terminal 4 on the ignition switch.

Power out from the switch is blue which crosses over to the LH cluster, then out to the bulb through either blue/white [UW] for main beam or blue/red [UR] for dip beam. A UW should also run to the console (blue) main beam warning light.

There should also be a second UW feed from the LH switch cluster to main beam from the headlamp flasher (dual horn/HL flash) button.

ag12680 said:

5. All the main harness connections have been checked.

Click to expand...

Well, it seems you've either missed something or there's a short you haven't found?

Your first photo shows no headlamp 'ground' return wire connected to the headlamp bulb holder? I assume you have fitted one (connected to harness red)?

Thank you L.A.B.

Yes, this was all with the ignition ON and with all grounds connected.

Your written description of the affected wiring led me to check and find that the R/H switch (though working properly) had the blue wire grounding to the handlebar through a tiny cut in the insulation. Now everything works.

Interestingly, what I thought was the small "pilot" bulb is labeled as headlight and vice versa. Signal lights have long blink times but I can get it on the road now.

Really appreciate your help!

Andy --

ag12680 said:

Yes, this was all with the ignition ON and with all grounds connected.

Click to expand...

Unless it's a Canadian model MkIII or has been fitted with a Canadian model ignition switch, then I can't explain that.

ag12680 said:

Interestingly, what I thought was the small "pilot" bulb is labeled as headlight and vice versa.

Click to expand...

I don't understand, sorry.

ag12680 said:

Signal lights have long blink times but I can get it on the road now.

Click to expand...

The 8FL flasher relay can be voltage sensitive so can flash slow on battery volts but faster when the engine has been running and the battery is up to full charge.