Hello All,
Thanks to all of you who responded. It sure is great to have you guys out there
to help. I've carefully read all of your posts. I think I'll explain a little
more what I've got.
Before that - any of you live here on the east coast and are going to some of
the events in the next few months. Is there an MGB-V8 get together around here
planned anytime soon ?
Rover V8, Mallory "Magnetic Breakerless Electronic Ignition System" which came
as one piece installed in a distributor, Diamond GT 63 12 volt coil which came
with the 75 MGB when I bought it, so I figure it's 20 years old. I started with
a GM distributor, put in a new vacuum advance unit and new points and condenser,
and then when I put it in the enging I realized that the drive dog was not
positioned correctly, and I needed to replace the bottom shaft with a Rover
length shaft. I opted for the convenient, and I thought much more robust
operation of the electronic ignition mounted in a distributor, and I got the
Mallory from Woody. The new (in 99 but now spare) coil, that I thought had
failed 1 1/2 years ago is a Wells C 841, 12 volt unit that says on the side
"use with external resistor", which to me means lower voltage with a 12 volt
coil.
When I test the + terminal on the coil with the ignition switched on, I show 14
to 15 volts. When cranking, it drops down to about 12 volts, so that resister
in the wiring isn't dropping the voltage to the coil. Looking at the 75 MGB
wiring diagram it shows a WLG wire from the fuse box and the distributor through
the squiggly line (in line resistor I presume) to the + terminal on the coil.
There is also another WLG wire directly from the starter solenoid to the +
terminal on the coil, which must provide 12 volts while cranking. After the
car is started, power must drop off of this wire, and then the car runs with
power through the in line resistor. However, when the engine is running on fast
idle, I'm reading 24 volts on the + terminal and about 12 on the - terminal. At
normal idle, it's 20 volts on + and 12 on -, so no indication of a voltage drop
through the in line resistor.
One thing not shown on the wiring diagram is a green wire from the - side of
coil through a small cylindrically shaped piece of blue plastic (like a
condenser in a distributor) that goes to ground. When I had my wife crank the
engine for me to test the coil voltage, I saw that this spade connector was
shorting out to the body of the coil making a spark. I'm not sure what this
function is, but if was shorting out, that can't be good, and maybe that has
been the cause of my problem.
Another oddity compared to the wiring diagram is that I have 3 wires from the
Mallory - red, brown, and green. I've got the red hooked up to the + terminal
on the coil, the green to the - , and the brown to ground. In the wiring
diagram it shows 3 wires, a WU which goes through a "distributor resistor", a W
which connects back to the WU after the "distributor resistor" before going
through the in line resistor and then to the + side of the coil. The third
wire, WB goes to the - side of the coil. With my mallory set up, I'm not using
a "distributor resistor" and the brown wire is running to ground instead of the
+ side of the coil, but that's how Woody said to set it up.
So, I'm going for a drive, thinking I may have sorted out the problem, with that
ground connection off the - side of the coil now not shorted out to the coil
body. I'll keep you posted.
Cheers,
Rick
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