At 10:41 PM 06/07/2000 -0400, you wrote about your 74 TR6:
> So the wire from the positive side of the coil had burnt off about 8"
>of insulation before the sheathing of the wiring harness. Then about a
>foot into the harness there was another inch exposed. I cut the thing
>off there and spliced in a new piece using my finest technique with a
>wire nut and electrical tape.
John,
On a 74 TR6 you have a ballasted ignition coil, if it is stock. Instead of
a discreet ballast resistor, they used a piece of special resistance wire
to drop the voltage to what that type of coil wants to see, when the car is
running (ISTR it is 7-9 volts). When cranking the engine with the starter,
a relay bypasses the ballast wire and puts full voltage on the coil input
to give some extra oomph to the start, but when the engine runs on its own,
the relay drops out and allows the ballasted wire to feed the coil at the
lower voltage.
If you have spliced in some "regular" wire in place of your burned section,
you now have less resistance over the length of the ballast wire, and thus
somewhat higher voltage at the coil input. One result of this will be that
your points will deteriorate quickly, and lead to poor running which could
look like carb problems, or whatever.
One moonless night, without a flashlight, I was on the side of the road
poking around the engine of my 74, and I mistakenly reconnected my ballast
wire to the negative tab on the coil. Before I caught the error, I had
smoke and a partially damaged ballast wire. Back home I spliced in some
regular wire to "get by" and the car did run, but never was right. I
couldn't locate any resistance wire so I added a discreet ballast resistor
in series with a new regular wire and that helped. Ultimately, I bypassed
the resistor and bought the Lucas Sport Coil, the input of which takes the
full 14V from your system.
Most of what I learned about it came from Dan Masters' ignition article
which is on the Web at the VTR maintenance site (thanks, Dan, and others on
the list!). I don't know why your ballast wire got hot enough to melt its
covering... it shouldn't. In my case, I did a dumb thing to cause it.
Maybe there is a problem in your coil where it is attempting to pull more
current than normal through the wire, leading to overheating of the wire.
So you want to determine the cause of the failure so it won't happen again.
I wouldn't worry about the backfiring carb until first making sure the
ignition is solid. Good luck!
Glenn 74.5 TR6 X 2
San Diego
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