On 15 Jul 95 at 11:28, Mgtd51@aol.com wrote:
> Instead of the coil terminals being denoted as SW
> and CB, they are + and -. The car is a positive ground.
> The coil when I hooked it up became too hot to touch; hot enough to start a
> fire. Why?
Didn't we do this last week? I know I did- in a very rare occurance, my MG
stranded me! Since the end of last season, my ZB has been intermittantly
cutting out a bit. Since I've been working out years of neglect, I attributed
it to dirt in the fuel system. In fact, changing the filter did clean things
up. But at times, it still did it some, and was possibly getting worse again
the last few days. The oddest part, was that turning on the lights helped
some.
Well, a week ago, with both kids in the car on the way to the sitters at 7 AM,
it gave out completly whiltst going down the road. Sorta cut out like I was
running out of petrol. A quick check of the float bowls yeilded no problem
there though. So I grabed the meter, and on to the ignition. 12 Volts at the
coil? Yup. At the points? Nope. Hmm. A check of the primary showed wide open.
Dead, burned out winding, ain't a-gonna go.
We had a nice long walk the rest of the way, where I got a ride home, picked
up a good coil, and back to the Magnette. 5 minutes later, she fired right up,
and I was on my way.
So, anyhow, you probably bought a coil that requires an external balast
resistor. There are 2 kinds, and you need an "internal balast" coil. The
wiring layout on new cars uses an extenal resistor, so that a higher voltage
can be fed to the coil while the battey voltage drops during starting, and
then feed through the resistor the rest of the time. If you hook up a
non-balasted coil with out a resistor, it will draw too much current, and get
quite hot. It'll also probably burn out your points pretty quickly.
Interestingly, when I later looked at my old coil, it was a non-balasted
Japaneese type. This explains my problems. The coil was slowly burning out
from over current- when I'd turn on the lights, and drop the system voltage,
the coil would get less, and run cooler and happier... for a while.
> Which terminal on the coil is attached to the distributor?
Your old coil, was marked sw and cb for SWitch and Contact Breaker (points),
and would have been used for positive ground systems. For your new coil, just
hook it up as marked- If you have positive ground, then you have "Negatice
Hot". Hook the - terminal to the ignition, and the + to the points
(distributer) side, which is the ground side of this curcuit. If you have a
negative ground car, or convert yours, simply reverse the wires. While the car
will run either way, there is a slightly better spark when hooked up the right
way.
For a little more, theres an article on just this subject on the TR6 web tech
pages, with some past discussion from the British-Cars list at:
http://www.mit.edu:8001/afs/athena.mit.edu/user/z/i/zimerman/www/Documents/tr6/tr6procedures.html
On a final note, while doing a bunch of other work on the ZB a couple of weeks
ago, I converted it from positive to negative ground. Not having a tach, the
job was almost insignificant, with one exception. This one now has an
electronic petrol pump, so I had to reverse it's leads, which lead to
replacing the rubber lines feeding it, and remounting it to get rid of the
isolation mounting someone went to a lot of effort to fabricate, as the pump
body was grounded. Making that mount surely took a lot longer than simply
reversing the battery leads, and breifly touching the field contact to + to
re-polarize it! I can just imagine what they did for the sterio that was once
installed as well.
________
/ _ \ Roger Garnett (Roger-Garnett@cornell.edu)
/ /|| \ \ Agricultural Economics | The Wayward Sports Car Centre
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