1973 Triumph harness
Now that I can trace things are OK
Ye-ea-ah ... you might want to stop and think about this ...
You've noted already that you'll have to add new cables to use the ammeter. Pete says, "a few things won't be in the right place" ... uh, yeah ... ime, a lot
of things "won't be in the right place".
Plus '73 and '69 handlebar switches are entirely different, '73 and '69 lights toggle switches are entirely different, yadda, yadda.
Also, a correctly-made '69 harness will have thicker main (Brown/Blue, Brown/White, White or White/Blue and Red) cables; standard '73 cables are too thin for the current they have to carry.
It isn't impossible
to connect a '73 harness to a '69 bike ... but it's a lot of faffing about. Add in that you're going to have a lot of unused cable ends anyway because you're fitting a electronic ignition and ime you run several risks:-
. you get fed up with all the extensions and cuts you have to make to make the connections;
. it looks crap when you've finished;
. it doesn't work;
. it's a 'mare to maintain.
Have you considered:-
a. simply swapping/selling/buying the '73 harness for a '69?
b. making your own?
The latter isn't as hard as it sounds. I'm hoping you've looked at the British Wiring
site and have either bought or are planning to buy decent tools and the correct cable and terminals? :bigt Rather than cobbling things together with those horrible red-, blue- and yellow-insulated terminals, random bits of cable and pliers?
If you're doing :bigt , you've got everything to need to build the harness your bike needs, rather than fiddling about with a copy of something designed nigh-on half-a-century ago. Plus the satisfaction of being able to say, "I built that".
except I have to figure how to wire in my ammeter
To use the ammeter,you won't be using the existing brown/blue battery lead.Tape that up,so it goes nowhere.
Run a new wire from the battery to one side of the ammeter.Join the other side of the ammeter to the brown/blue wires that connect to the ignition switch.
Ahhh ... no. How will the alternator/rectifier charge the battery? The "existing" ('73) Brown/Blue connects the rectifier to battery -ve as well as the Zener and ignition switch.
If you look at the '69 diagram, you'll see Brown/Blue runs just from battery -ve to one side of the ammeter (and the horn or twin horns relay). In addition
, Brown/White runs from the rectifier to the other
side of the ammeter, as well as connecting to the Zener and the ignition switch.
In practice, it doesn't matter whether Brown/White or Brown/Blue connects to the Zener and the ignition switch; however, if you want the ammeter to indicate both charge into and discharge from the battery (as it does as standard), it does
matter that the rectifier and battery -ve are connected to different sides of the ammeter. Then it's good practice to connect the Zener directly to the rectifier.
The horn will be wired differently
'69 the horn (or twin horns relay) must
be insulated from its mounting, because battery -ve is connected to one side of it while the handlebar button is connected to the other side, and then battery +ve. So the horn/relay is 'live' all the time, just pressing the button makes the circuit and sounds the horn(s).
Otoh, '73 the horn button
is supplied from the ignition switch by a White cable (which won't become 'live' 'til the ignition switch is 'on') and it's the horn button
that supplies the horn, through the Purple/Black cable. The original '73 horn would still have been insulated from its mounting, and have a Red return cable as well as the P/B from the horn button, but cheapo pattern horns can return via their mounting bracket.