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JC1
08-24-2012, 09:46 AM
Guess I still need some clarification. MY 1973 TR-6, with presumed totally original wiring (second owner 32 years),has only ONE wire from the wiring harness to the positive side of the coil.

I have always thought/read ALL 1973-76 TR-6 were ballasted systems, needing a 1.5 ohm coil when using the Pertronics
ignitor. Parts vendor catalogs seem to confirm this.

Of the several wiring diagrams I have checked, some show one wire to the positive side of the coil for a 1973, while others show two wires to the positive side of the coil.

Is it possible to have a ballasted wiring harness with only one wire to the positive side of the coil ?

How could I check the system to determine if ballasted ? Car was built in early 1973, so I am concerned it was transitional and actually needs the 3 ohm coil.

DNK
08-24-2012, 10:22 AM
Only answer I could come up with is that it was a very early 73 and still used a 1 wire set up.
You sure that the coil is correct for a ballasted set up?
Have you checked it?

TexasKnucklehead
08-24-2012, 10:23 AM
Is it possible to have a ballasted wiring harness with only one wire to the positive side of the coil ?


On a 32 year old car, much is possible. It's also possible the wiring diagram you checked is not accurate.
try these: https://advanceautowire.com/tr2506.pdf

The balasted resister wire is not stranded wire as you can see in my picture. It is solid and easily broken. I've rewired mine and aded the external resister, but here's a before picture.

TR6oldtimer
08-24-2012, 11:36 AM
I have a '73 with a build date of Nov '72, comm no. CF 2761. It has the two wire circuit.

There was a significant change in the wiring between the 72 and 73 models, and that involved the removal of the ammeter in the '73 and later models. While on the surface, the replacement of the ammeter with a volt meter may not seem like a big deal, it in fact required a new design of the car's wiring harness. I do not see that an early version of the '73 harness would omit the two wire ignition coil design.

That said, it is a Triumph, and who knows what they did.

For information, the pink/white ballast wire is in the run circuit off the ignition switch. The white/yellow wire is not ballasted. It connects to the starter solenoid and provides full voltage to the coil on startup.

Tim Tucker
08-24-2012, 03:40 PM
Any chance the wiring harness tag is still in place? I found mine at my left foot when driving at the dimmer switch. That will give you your harness part number.
Good Luck
https://www.tidentenn.com/CC78xxxLO/92%20(misc%20TR6%20Projects)/Wiring%20Tag/hi-res/back.jpg https://www.tidentenn.com/CC78xxxLO/92%20(misc%20TR6%20Projects)/Wiring%20Tag/hi-res/front.jpg

TR3driver
08-24-2012, 05:40 PM
How could I check the system to determine if ballasted ?
Hook up the coil you have to the wire you have. Close the points (or jumper around them), then turn the key on and check the voltage across the coil. Do this fairly promptly (within a minute or so) and turn the key back off, JIC you have a 1.5 ohm coil without a ballast. (A minute or two won't hurt anything, but don't leave it on for a long time.)

If you find close to 12v, there is no ballast resistance in the wiring to the coil.

Brosky
08-24-2012, 06:52 PM
This is what the original wire looks like on a 74 (wires in sheath on left)