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Fitting a cooling fans override switch to an MGBGTV8
Victor Smith (Harvest Gold 1089) longed to be
able to turn on the cooling fans in anticipation of a heat build
up in slower traffic, so finally got round to making the modification
and found it was a straightforward job. (Oct
08)
Over
many years of enjoyable motoring with my V8 I had often thought
it would be good if I could switch on the cooling fans when
I sensed the approaching traffic conditions would cause a build
up of heat in the engine bay. I wanted to be able to do that
well before the Otter switch clicked in. Well at last the job
has been done and my word it does feel better to be in control
of the fans!
If you remove the spade connector from the Otter switch and
touch it to earth on one of the studs on the thermostat housing,
the fans come on. This provides the clue as to how the override
can be carried out. If you trace that cable back (marked BO
on the wiring diagram, black with an orange trace), you will
find it crosses the offside rocker cover and ends up on a terminal
on the cooling fans relay fitted to the offside inner wing next
to the fuse box. So popping in some new wiring to a simple switch
mounted near the driver which earths that connection will provide
the override.
So first thread through some black 5 or 8 amp cable from a point
near the ignition switch, through the rubber grommet in the
bulkhead behind the brake master cylinder reservoir and along
by the main wiring harness to the relay. Take care with the
grommet because ageing may well have removed much of the flexibility
and it can easily fall out. Then locate a simple toggle switch
within convenient reach of the driver. There are two useful
locations - either mounted in a switch bracket fixed to the
fixing screw on the top side of the radio speaker casing in
the driver's legwell or alternatively in a convenient hole in
a substantial metal bracket located just below the dashboard
and to the right of the steering column. Then connect one of
the switch terminals to a spade connector on a short length
of cable with the other end fixed to a convenient earth nearby.
The end of the black
cable threaded through earlier then has
a spade connector fitted which is
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The
original cable from the Otter switch is removed from the righthand
terminal of the cooling fans relay above and refixed to a new
piggy back spade connector (blue above) which also carries the
lead (black above) from the new override switch.
pushed
onto the second switch terminal. The two cables are then tidied
away.
Returning to the cooling fan relay, pop a new
piggy back spade connector (blue in the photo above) on the
end of the black cable threaded through earlier. Then pull off
the spade connector of the cable (black with an orange trace)
from the Otter switch, locate the piggy back connector on that
relay terminal and then push the Otter cable connector onto
the additional terminal of the piggy back connector. You then
need to tape the new black wire onto the main wiring loom with
black insulating tape to tidy up the job.
Switch on the ignition and test - operating the toggle switch
from the driving seat should turn the cooling fans on and off.
Earthing the lead on the Otter switch should cause the fans
to come on. Run the engine up until the needle reaches around
the 4pm position on the temperature gauge and wait for the fans
to come on as the Otter switch clicks in. That will complete
your test.
All
the parts you will need can be obtained very easily from any
good motor supplies shop or from Halfords. You will need a mixed
bag of auto wiring fittings including a piggy back spade connector,
spade connectors, a toggle switch, a switch mounting bracket,
a couple of metres of 5 or 8amp black cable and some insulating
tape.
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