On mine the main ground cable goes from the battery
POS to the top left of the cylinder head.
Once I forgot to hook this up and indeed the thinner wires were carrying all the ground and started to burn up.
That is the reason for not
having a harness wire connected to the battery
positive terminal as stated in the service bulletin so if you have one fitted now then it's better to remove it.
Of course I then installed the ground cable but I later discovered that its connection to the cylinder head was loose. So I remedied that but I'm now thinking I should install an auxiliary ground.
There shouldn't be any need for an "auxiliary ground" as long as the connection remains tight (self-locking nut?) or move the existing cylinder head ground cable closer to the starter motor.
Should it be from the starter motor casing to either of the two locations Tridentman nicely provided?
Why not just move the existing cable to (or closer to) the starter motor? An additional cable running from the starter motor to one of the previously mentioned locations makes no sense unless the ground cable to battery
positive is also connected there.
A ground to the frame only (as one seems to be) not including part of the engine case would be a step in the wrong direction in my opinion.
Where on the starter should I start this wire? I noticed that in the casting that is between the starter motor and the inner primary case there is a mystery hole drilled and tapped (about 5/9" diameter) and it has a rubber plug over it for some unknown reason
I don't know of any 5/9"(!?) diameter tapped hole with a rubber plug in the starter motor housing.
Edit: The casting has a boss on the top with a 0.4" hole to take the rubber bung that supports the airbox but it wouldn't normally be tapped. https://www.triumph-spares.co.uk/rubber-buffer-82-7835
so maybe I can just attach the extra ground wire from the Tridentman locations to there?
Seems a bit redundant to wire from a casting to a casting/engine bracket. Should I instead run the auxiliary ground wire from a Tridentman location to the battery POS terminal?
If you attach a ground wire to the starter motor then the logical thing to do would be to connect it to the battery
(+) then you wouldn't need the existing ground wire.