I know the heater fan on MGBs is one of the things that can benefit from
being 'relayed'. They all should benefit, but cars fitted with an ignition
relay may benefit less than those without, since the green circuit is
already powered from a relay - albeit via a fuse.
PaulH.
----- Original Message -----
From: Tab Julius <tab@penworks.com>
To: <mgs@autox.team.net>
Sent: Wednesday, November 24, 1999 10:32 PM
Subject: Anybody ever try this heater technique from Moss?
> 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?
>
> -----------------------------------------
>
> 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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