Mystery Wire II

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crusadersports

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Can anyone tell me what this wire is for on my MK3? It's lost its insulation, so much so I can't see what colour it was without cutting further into the loom. I have a vague recollection it was an earth wire that went to the headsteady, but with the isolastics I wonder if this really achieved anything?

Should've said I can't find my wiring diagram anywhere... Is it available online?

Many thanks all :) Sorry about the hazy photo

Mystery Wire II
 
Hi, welcome! Is that a bit of yellow insulation near the loom? Or just the bare copper as the rest is? Slice a wee bit of loom wrap... peak in
 
I can't tell. Test it for continuity to a known ground. If not a ground wire, check it to see if it is "live"; you don't want a live wire shorting out to ground. I have a ground wire with an eyelet in the same general area, where other ground wires are also connected. If you can't tell, don't be shy about trimming back the harness a little; you can cover the area back up with a little harness tape. The only useless wires are the extra wires for Interpols and the "hot" red/white wire from the right switchgear.
 
crusadersports said:
Can anyone tell me what this wire is for on my MK3? It's lost its insulation, so much so I can't see what colour it was without cutting further into the loom. I have a vague recollection it was an earth wire that went to the headsteady, but with the isolastics I wonder if this really achieved anything?
Click to expand...

Well the "earth" wire to the headsteady was there because of the isolastics, it provided an earth for the otherwise rubber insulated engine. Previously, I assumed if this was missing, then there would be no return path for the current flowing through the spark plugs, although I was corrected by someone on the forum..
 
How, might I ask, did it lose its insulation? You might want to cut into the loom for more than just identification! Usually the old tape is getting brittle with age and wrapping it with new tape isn't a bad idea anyway.

Russ
 
Old Bloke said:
Well the "earth" wire to the headsteady was there because of the isolastics, it provided an earth for the otherwise rubber insulated engine. Previously, I assumed if this was missing, then there would be no return path for the current flowing through the spark plugs, although I was corrected by someone on the forum..
Click to expand...

If the starter motor is operational, then for the MkIII model, the return path for the complete electrical system should go from the harness to the engine, and then back to the battery through the heavy positive starter cable.
Connecting a secondary return from the harness to the battery positive terminal (as shown on the Mk.III wiring diagram :x ) is a serious electrical error, as there is a chance that should a heavy starter positive lead terminal be left disconnected or become loose or go high resistance, then 100A+ of electric starter current will attempt to return to the battery through the un-fused secondary harness wire when the starter is operated. :shock:
 
L.A.B. said:
Old Bloke said:
Well the "earth" wire to the headsteady was there because of the isolastics, it provided an earth for the otherwise rubber insulated engine. Previously, I assumed if this was missing, then there would be no return path for the current flowing through the spark plugs, although I was corrected by someone on the forum..
Click to expand...

If the starter motor is operational, then for the MkIII model, the return path for the complete electrical system should go from the harness to the engine, and then back to the battery through the heavy positive starter cable.
Connecting a secondary return from the harness to the battery positive terminal (as shown on the Mk.III wiring diagram :x ) is a serious electrical error, as there is a chance that should a heavy starter positive lead terminal be left disconnected or become loose or go high resistance, then 100A+ of electric starter current will attempt to return to the battery through the un-fused secondary harness wire when the starter is operated. :shock:
Click to expand...

Thanks for pointing this out LAB. I wonder if that is what has happened to my bike. The insulation from the wire is just not there- may be because a PO did run an earth to the head steady and it got frazzled like you describe. :shock:

The timing of this is fortuitous- I have the beefed up starter cable kit from the CNW. It comes worth 4 cables. When I enquired what the fourth one was for, I was told this was intended as an earth to the frame, meaning any number of electrical components (indicators for example) could be individually earthed. If I've understood all this, it sounds to me like this would be a very bad idea with a MK3 :oops:

Are there any other errors for the unwary on the MK3 wiring diagram (now secured, thank you :) )?
 
L.A.B. said:
Old Bloke said:
Well the "earth" wire to the headsteady was there because of the isolastics, it provided an earth for the otherwise rubber insulated engine. Previously, I assumed if this was missing, then there would be no return path for the current flowing through the spark plugs, although I was corrected by someone on the forum..
Click to expand...

If the starter motor is operational, then for the MkIII model, the return path for the complete electrical system should go from the harness to the engine, and then back to the battery through the heavy positive starter cable.
Connecting a secondary return from the harness to the battery positive terminal (as shown on the Mk.III wiring diagram :x ) is a serious electrical error, as there is a chance that should a heavy starter positive lead terminal be left disconnected or become loose or go high resistance, then 100A+ of electric starter current will attempt to return to the battery through the un-fused secondary harness wire when the starter is operated. :shock:
Click to expand...

Grief, that would make your day wouldn't it! Leaving off any of the high current leads from a conventional starter motor usually means that the starter motor just won't take any current. Was that too boring for Norton? :p
 
Old Bloke said:
Grief, that would make your day wouldn't it! Leaving off any of the high current leads from a conventional starter motor usually means that the starter motor just won't take any current. Was that too boring for Norton? :p
Click to expand...

Whoever designed the 850 Mk.III Commando wiring harness obviously designed the T160 harness as it also had the same error, a few months after the release of the T160, Triumph issued a service bulletin to their dealers instructing them to cut off the ring terminal and tape the wire back to the harness of every T160 they encountered that still had it attached.

I don't know if a similar service bulletin was ever issued to Norton dealers.
 
I can see the potential problem, but if the only ground from the battery is to the engine, then how do all the other electrics get their ground in the Isolastic system?
Jaydee
 
jaydee75 said:
I can see the potential problem, but if the only ground from the battery is to the engine, then how do all the other electrics get their ground in the Isolastic system?
Click to expand...

I did say previously that:
If the starter motor is operational, then for the MkIII model, the return path for the complete electrical system should go from the harness to the engine and then back to the battery through the heavy positive starter cable.
Click to expand...

So: harness-engine-battery, not: engine-harness-battery as it is in a non-electric start system and the harness return/ground to the head steady suits either.
 
L.A.B. said:
Old Bloke said:
Grief, that would make your day wouldn't it! Leaving off any of the high current leads from a conventional starter motor usually means that the starter motor just won't take any current. Was that too boring for Norton? :p
Click to expand...

Whoever designed the 850 Mk.III Commando wiring harness obviously designed the T160 harness as it also had the same error, a few months after the release of the T160, Triumph issued a service bulletin to their dealers instructing them to cut off the ring terminal and tape the wire back to the harness of every T160 they encountered that still had it attached.

I don't know if a similar service bulletin was ever issued to Norton dealers.
Click to expand...

So an earth wire to the head steady is a bad idea (on a MK3 with working electric leg).

'So: harness-engine-battery, not: engine-harness-battery as it is in a non-electric start system and the harness return/ground to the head steady suits either'.

So an earth wire to the head steady is a good idea (on a MK3 with working electric leg).

Sorry LAB, call me daft but I don't understand the distinction. How do you ensure these earthing points are all in the right order when the wiring diagram is suss?
 
crusadersports said:
So an earth wire to the head steady is a bad idea (on a MK3 with working electric leg).

'So: harness-engine-battery, not: engine-harness-battery as it is in a non-electric start system and the harness return/ground to the head steady suits either'.


So an earth wire to the head steady is a good idea (on a MK3 with working electric leg).

Sorry LAB, call me daft but I don't understand the distinction. How do you ensure these earthing points are all in the right order when the wiring diagram is suss?
Click to expand...

It's not the head steady wire that's cause of the problem. The problem is when a secondary earth/ground/return harness wire is connected to the battery positive terminal in addition to the heavy gauge positive starter wire as it can cause the high starter current to take an alternative return route to the battery = through the harness.

Mystery Wire II
 
christulin said:
Wouldn't that just blow the fuse?
Click to expand...

No, because the fuse is on the negative side of the battery and the high Amp supply current for the starter obviously doesn't pass across the fuse.
 
My T160 wiring diagram shows separate wiring directly from the battery to the starter (starting assisting motor) though a relay. There is a fuse between the battery and the other stuff.
 
christulin said:
My T160 wiring diagram shows separate wiring directly from the battery to the starter (starting assisting motor) though a relay. There is a fuse between the battery and the other stuff.
Click to expand...

Yes, your point being?
 
L.A.B. said:
crusadersports said:
So an earth wire to the head steady is a bad idea (on a MK3 with working electric leg).

'So: harness-engine-battery, not: engine-harness-battery as it is in a non-electric start system and the harness return/ground to the head steady suits either'.


So an earth wire to the head steady is a good idea (on a MK3 with working electric leg).

Sorry LAB, call me daft but I don't understand the distinction. How do you ensure these earthing points are all in the right order when the wiring diagram is suss?
Click to expand...

It's not the head steady wire that's cause of the problem. The problem is when a secondary earth/ground/return harness wire is connected to the battery positive terminal in addition to the heavy gauge positive starter wire as it can cause the high starter current to take an alternative return route to the battery = through the harness.

Mystery Wire II
Click to expand...

So (assuming positive earth) the main earth is the red cable running from the positive terminal to the crankcase stud behind the barrel. You're saying a secondary earth wire from the positive terminal (as depicted on the factory wiring diagram) is bad? Ok, so as I don't have this bad secondary earth wire, does this mean an earth wire to the head steady is therefore a good idea? If the frame is isolated from the circuit because of the isolastics, I don't see the point in an earth wire to the head steady. I can't see one on the diagram, but I think that is what I have in the picture in the first post.

Thanks for your help with this LAB. We'll get there, I promise! :mrgreen:
 
crusadersports said:
L.A.B. said:
crusadersports said:
So an earth wire to the head steady is a bad idea (on a MK3 with working electric leg).

'So: harness-engine-battery, not: engine-harness-battery as it is in a non-electric start system and the harness return/ground to the head steady suits either'.


So an earth wire to the head steady is a good idea (on a MK3 with working electric leg).

Sorry LAB, call me daft but I don't understand the distinction. How do you ensure these earthing points are all in the right order when the wiring diagram is suss?
Click to expand...

It's not the head steady wire that's cause of the problem. The problem is when a secondary earth/ground/return harness wire is connected to the battery positive terminal in addition to the heavy gauge positive starter wire as it can cause the high starter current to take an alternative return route to the battery = through the harness.

Mystery Wire II
Click to expand...

So (assuming positive earth) the main earth is the red cable running from the positive terminal to the crankcase stud behind the barrel. You're saying a secondary earth wire from the positive terminal (as depicted on the factory wiring diagram) is bad? Ok, so as I don't have this bad secondary earth wire, does this mean an earth wire to the head steady is therefore a good idea? If the frame is isolated from the circuit because of the isolastics, I don't see the point in an earth wire to the head steady. I can't see one on the diagram, but I think that is what I have in the picture in the first post.

Thanks for your help with this LAB. We'll get there, I promise! :mrgreen:
Click to expand...

Oh, Lab will correct me here :) but I'll try and give my view on what he means.

In his diagram above

1. The wire marked R going to the "Engine Earth(Starter)", Is the thick cable designed to return the current flowing through Starter motor possibly 100amps to earth(the battery +ve in the Command).
2. The wire marked R which Lab has marked with a big red X is an earth connection, probably to the head steady, this would be a normal wire in your harness designed to take maybe 20 amps.
3. This is the wire that Lab said should not be fitted to the headsteady as it was a mistake in the diagrams because...

..if the thick cable breaks, or gets disconnected, then the current through the starter motor will return to the battery through the normal wire, and as this wire can only take @20amps, running 100amps through it will likely fry the wire right through your wiring harness. Messy.

So I think what Lab is saying is that Mk3 with the starter motor should not have the secondary earth to the headsteady.
 
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