In a message dated 97-05-30 19:56:45 EDT, boballen@sky.net (Robert Allen)
writes:
> A friend of mine has a late model with idiot lights. He would like to
> add oil temp and pressure gauges and, perhaps, water temp. If anyone has
> been down this road I'd be curious about your experiences:
>
> 1) brand & size of gauges
> 2) mechanical or electrical
> 3) where to mount in car
> 4) how to connect to motor
> 5) any oops to be aware of
Bob:
1) Most aftermarket gauges are 1 1/16 " diameter, same as the Lucas units
used in the TR6, and fit into the standard gauge holes exactly. I assume the
gauges in a Spitfire are the same. The most common brands are Auto-Meter,
VDO, and SW. I only have experience with VDO. I have had a clock from VDO in
my TR6 for a few years now, with no problems. Only recently have gauges been
available in a larger size. A few of the lesser known brands make smaller
gauges. The larger sizes are nice, but they can be hard to fit in these small
cars. I'm using 2 5/8 " units in the TR5.0, but they "just" did fit. I had to
modify the sheet metal dash backing a little.
2) Many people are of the opinion that the mechanical gauges are more
accurate than the electrical gauges. I suspect this is no longer true, with
the new three wire gauges now being offered. In spite of being called three
wire, there are actually four wires - power, ground, signal input, and lamp
input. The older gauges were of the thermal type. The three wire gauges have
two coils, and operate on a voltage differential principle. In other words,
the gauge reads according to the difference between the battery voltage and
the voltage produced by the sender resistance. If the battery voltage goes
down, for example, it goes down both at the power input to the gauge, and at
the sender. Thus, the difference remains the same. As a result, no regulator
is required.
One plus for the mechanical gauges is their expanded dial scale. For a
temperature gauge with a range of 0-180 degrees for example, an electrical
gauge may cover the range over 120 degrees of the dial face, whereas, on a
mechanical gauge, the same 0-180 degrees may cover 270 degrees of the dial
face. This makes it much easier to read small increments on the mechanical
than on the electrical. For street use, this advantage is probably not
important.
3) Any place thats convenient to read without taking your eyes off the road
too long, and is not obstructed by the steering wheel (To read the Temp gauge
on the TR6, I have to move my head a good bit to see around the steering
wheel. On the TR5.0 project, I put the gas gauge where the temp gauge
normally goes. I don't need to check the fuel gauge as often). If you use
electrical gauges, there is no restriction on where you place them - an
advantage of the electrical over the mechanical. For mechanical gauges, you
need to keep in mind the routing of the tubing. It is not as flexible as
wires.
4) The senders normally screw in where the switch for the idiot light goes.
If you want to keep the idiot light, tee fittings are available, allowing you
to fit both units. For new parameters, such as oil temperature, you may have
to improvise. You might drill a hole in the pan, for example, or the sender
may come with a fitting that adapts to the oil drain plug. I can't think of
anything that might require an exotic setup, that you might want on a street
machine. For any parameter that manufacturers provide gauges for, there is
usually a straight forward way of mounting the sender. Most manufactures
offer a wide range of fitting types, for both metric and SAE threads, in a
range of sizes.
5) Nothing other than the normal precautions. For wiring, connect the power
lead to the green wire circuit if you anly want it on when the key is on, and
to the purple wire circuit if you want the gauge to read all the time (clock,
for example). If you connect to the green or purple wire circuits, there is
no need for additional fuses, as these wires are already fused. If you find
it more convenient to connect to a brown wire circuit, be sure to use fuses,
as the brown wires are not fused. As in all cases, place the fuse as close to
the power source as possible, not close to the gauge. For both the wires and
the mechanical tubing, check the routing very carefully to ensure there is no
rubbing on any sharp edge, and that there is sufficient slack so when the
motor moves, they don't get broken. Check the installation often for the
first few trips, looking for any signs of damage, or potential for damage.
Make sure the steering wheel, steering shaft, foot pedals, or other moving
components do not foul the wires or tubing as these components are operated.
If you use tee fittings, or other adaptive mechanisms, don't let the assembly
hang out far enough that it might break off when you hit a road bump, or
vibrate so bad as to crack form being too flexible.
That's about all I know about the subject, hope it is of some help.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition
'68 MGBGT---organ donor for the '74
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