Helped a fellow club member fix an interesting problem with the MDS ignition
in his '73 TR6. If this is old news --- sorry.
The car ran great but wouldn't stop when the ignition was switched off. If
he tapped his brakes, the engine would shut off. (He said that was good
British logic; if you want it to stop, hit the brakes.) He said the MDS
module was installed as per instructions, wires directly to 12 volts and
ground and also a wire to the white ignition wire at fuse block. ( I assume
there was also a wire or two to the coil, didn't think to check.)
There was obviously some source of 12 volt power to the ignition wire with
series resistance such that it was loaded down by the brake lights (also
powered from the white wire --- but after the fuse so it is the green wire).
Checked out Dan Master's schematic for the '73 and noted the Alternator
Warning Lamp (IGN) from the alternator voltage sense circuit connects to
the white wire. We pulled the lamp and everything worked properly (except
the lamp). We installed a diode in series with the warning lamp and
everything now works as it should.
The problem may have been compounded by engine modifications such as three
big Weber Carbs and I believe a shaved head & high lift cam. The idle was
set faster than norm to smooth out the jumping at the curb. That may
cause the alternator output voltage to be above normal for idle.
Nelson Riedel
Granville, OH
76 TR6 (just painted, now repairing damage from fender bender)
68 TR250 (next project - new paint)
70 TR6 (all the parts in a pile ready to assemble)
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