I found this on the Moss tech-tip page. Would it still hold true for a 78B
(wiring being insufficient, that is?). Has anyone here ever tried it?
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Increase Your MGA, MGB Blower Motor Power
On many cold winter days, I have wished that the blower motor on my MG
would run at a higher speed to keep up with the air being sucked out
through the many cracks and crevices in the cockpit.
While replacing the fan, I noticed that the motor ran much faster being
connected directly to the brown circuit at the fusebox. I decided to do
some voltage and current measurements on the factory wiring harness and
found that the original wires are of insufficient size to carry the
necessary current to the fan motor. With the motor in operation, voltage
fell from 12 volts to 9.7 volts and current was only 2.6 amps. Hooking the
motor directly to the brown circuit at the fusebox and bypassing the
smaller gauge wires resulted in a voltage drop of only one volt and a
higher current supply to the motor of 3.5 amps.
To remedy the problem of the slow running fan motor, I installed a relay
(Moss #542-235) in the fan motor circuit, and tapped voltage from the
purple (fused) side of the fusebox. On the MGA, I used the same method, but
tapped fan motor voltage from the brown/green (horn) side of the fusebox.
The relay, along with 12 gauge wire, supplies the motor with the current it
needs, without the large voltage drop associated with the smaller wires,
and greatly increases the amount of air delivered by the heater.
Wiring diagram at:
http://www.mossmotors.com/techtips/pictures/127.gif
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