This is how I took a mildly useless gauge and turned it into
something that actually gives you useful information. This information is being
presented so that other Miata owners may modify their cars as I have done. USUAL
DISCLAIMER: Use this info at your own risk, just because it works for me doesn't
mean it will for you, research application and compatibility before taking tools
to your car. If this modification summons aliens to your house, not my fault! :)
Wallyman
The stock Miata temperature gauge is fine for normal people. Being a guy that
runs a turbo modified Miata, I'm far from the norm. The car gets hot,
reaaaaaally hot when driven hard for any length of time, and I like to frequent
the racetracks on occasion. So, the temperature gauge that serves normal folks
well does not do so good for a modified car that relies on accurate and quick
temperature monitoring.
STOCK: The stock gauge needle moves in a fashion similar
to this:
Basically, if the car is warm and anywhere between 180 and 235
degrees, the needle will point up, and your average driver is happy as a clam.
The only time the needle flinches is during warm up and when something evil has
begun (or completed). When the needle starts to move towards "hot", the car is
actually already very hot (240 degrees), and should be checked immediately to
avoid possible damage. This is all fine and dandy for a unmodified car, but the
forced induction (turbo and supercharged) Miata has a tendency to get hot in a
hurry, so by the time the gauge wiggles, you are opening the wallet to replace a
bunch of expensive parts.
MODIFIED: The modified gauge is just what most
old-school guys/gals would expect. If it is half way to hot, the needle reads
half way.. if it is ¾ hot, it reads ¾. Rather commonsensical, don't ya think? Of
course, a wiggling gauge is scary to normal people! :)
Seems like such a simple concept, but for the sake of not
having to answer a ton of "Why does my temperature needle move?" questions, I
assume that Mazda made it the way they did. And that's fine, but not for me...
so off to the electronics store we go!
The tools you need:
Solder iron
Solder
Solder Sucker, or wick
Small needle nose pliers
Small wire cutters, preferably side cutter (nippers)
Drill
Small drill bit (???? 1/16th inch?)
Patience
Steady Hands
The parts you need:
82 ohm, 5 watt resistor
55 ohm, 5 watt resistor
16 ohm, 5 watt resistor
150 ohm, 1 watt resistor - "COLD" Calibration Resistor - equivalent
to about 150 degree Fahrenheit
NO IMAGE
20 ohm, 1 watt resistor - "HOT" Calibration Resistor - equivalent to
about 270 degrees Fahrenheit
NO IMAGE
2" piece of small wire, 22 AWG is fine (I used a piece of cut off
resistor leg)
Heat Shrink tubing/electrical tape (tube must fit over 16 ohm
resistor)
NO IMAGE
The modifications are as follows...
Remove Cluster
Remove 2 screws on Kick Panel below the steering column
Remove the 4 screws that hold the steering column/lock cylinder
cover in place (see picture 1a)
Remove the 2 screws in the bottom of the cluster shroud
Remove the 4 screws that hold the cluster in (see picture 1b)
Unhook the 2 large wiring harnesses on the back of the cluster (see
picture 1c)
Unhook small wiring harness on the back of the cluster
Unhook the speedometer cable (push down on the raised bar on the top
of the connector while pulling out gently on the cluster) (see picture
1c)
Take the cluster to the workbench
Disassemble the Cluster
CAUTION - Do not touch the gauge faces, fingerprint oils will not
come off!
CAUTION - Do not remove the needles, or bump them. You don't need to
mess with the needles at all for this modification.
CAUTION - Don't let anything get inside the clear plastic cover once
it is removed. Don't touch the inside of it. Don't scratch it!
Remove the clear plastic cover
Press in the black tabs while gently pulling out on the clear
assembly. Start at one end, applying pressure while pushing them in,
and it should work fine. (see picture 2a)
If you are having trouble with it clicking itself back together,
stick a small screwdriver in between the cluster and the clear piece
as you work your way around.
Make sure the wiring harness comes out through the hole in the
casing, you will probably have to pull the circuit trace part back a
little to feed it through the hole. Bending it won't hurt the traces,
so move it as needed. Make a note of how it was routed so it is
reassembled the same. (see picture 2b)
Remove the Temperature Gauge Assembly
Remove the 3 screws on the back side that are holding the gauge in
(see picture 3a). Gauge may fall out, so be mindful of it coming loose.
Pull gauge out the front of the cluster, set cluster aside (make
sure the faces don't get touched!)
Modify the Temperature Gauge
Remove the 82 ohm resistor (see picture 4a)
Heat the solder on the back (see picture 4b)
Suck/wick hot solder away
Bend legs over on resistor so it will pull out
Pull out resistor from front side
Install the 82 ohm, 5 watt resistor
Bend legs over on the new resitor
Insert legs into holes from the top side. Make sure to leave it up
off the board so it isn't touching anything and air can get around it on
all sides.
Bend over ends of tails on back side
Solder points on the board on the back side
Nip off the tails of the wires you just soldered
Bend the resistor as needed to maintain air gap on all sides.
Remove the Zener Diode (see picture 6a)
Heat the solder on the back (see picture 6b)
Suck/wick hot solder away
Bend legs over on zener diode so it will pull out
Pull out zener diode from front side
Using the drill and a very small bit, enlarge the power side hole of
where the Zener Diode was (see picture 7a)
Drill small hole in ground trace, just above existing diode solder
location (see picture 8a)
