Morris:
To upgrade from a one speed to a two speed fan, you need the following:
1) About three feet of wire
2) A two-speed switch from a later (79-80) MG
3) The fan motor from a later (79-80) MG
A two speed switch means a two speed resistor somewhere in the fan motor;
earlier motors don't even have the wiring for this. You can spot a two-speed
fan real quick because it's got three terminals on it; earlier fans only have
two. MOSS and others should have them listed by model years.
In order to get two speeds, you have to have three wires coming out of the
switch: hot in, hot out1 and hot out2. Your switch now has just two - hot in
and hot out. The second hot out wire corresponds to the higher fan setting.
You must have a two speed fan mounted in the front of your heater box in
order for this arrangement to work. Running the second wire is no great feat,
but you have to watch the colour codes on the existing wires pretty carefully
so that when you get to the fan, you know what you're doing.
After all this, I'm not certain that the second speed on a two-speed fan is
any higher than the only speed on your one-speed fan. If you do all of this,
let me know. I can take that off of my 'idle curiosity' back burner.
ckr
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