working: suspect the sending unit. A good
sender will measure 1000 ohms resistance cold,
60-80 ohms at operating temperature (with the
wire lead disconnected, red lead of the meter on
the sender's terminal and the other to a ground
such as cylinder head). If the resistance stays
very high even when warm, your sender is bad.
Also see this
link. It tests the resistances across the
Hot: surprisingly the standard operating
temp is at the 3/4 mark on the gauge. High by
modern gauge standards but normal for
Spitfires/GT6's. Don't let the needle go into
working: If fuel gauge are reading always
empty or full suspect wiring trouble. Showing
empty is electricity not making it to the gauge.
Full is a short.
Reading: If gauge constantly reads low or near empty suspect the sending unit. The float will often develop a leak allowing it to become filled with gas and no longer float.
link for a how to for sending unit
If both temp gauge and fuel gauge are reading
incorrectly suspect the voltage stabilizer. It
is mounted on the back of the Speedometer.
To test the stabilizer get an analog voltmeter
and open the center section of the dash. Pull
the green wire that attaches to the fuel gauge,
and attach your positive lead there, ground the
negative lead, and turn on the ignition. If you
are measuring 10 volts constant, then the
voltage stabilizer is fine. If not check that is
is properly grounding (clean all contacts and
make sure its mounting screw is tight).
Needle: The cable is sticking internally.
Remove the cable from its housing. Inspect for
fraying or kinks. If you see anything like that,
replace the cable. Otherwise, give the cable a
liberal coating of graphite. This comes in
either a tube or a spray can (be sure to wear
some disposable gloves...it's messy stuff.)
Re-insert the cable and make certain that the
ends are seated fully into the distributor shaft
housing and the gauge.
working: The cable can break internally.
The bearings in the tacho can partially seize
breaking the cable.
Tachometer (electric, MkIV and 1500)
working: Being a very simple system the
usual cause for a non-working tach is dodgy
wiring. Check grounds and to see if tach is
working: 99% of the time the cable
between transmission and gauge is broken
internally. Later US cars had an "emissions
check" box in the middle of two cables rather
than one long cable. This box often seizes up
braking the bottom cable. The best fix is to
bypass the box with a single cable.
The gauge can also cause the breakage. The
bearings in the speedo and tacho can partially
Page dedicated to troubleshooting
Describes the systems controlled by each
fuse (from 1975 Owners Manual).
Describes the relays on late model Spits
Links to download some excellent wiring
diagrams by Tom O'Malley
Information about the front lights on early
Testing of the standard Lucas Control Box or
Voltage Regulator installed on all Triumph
Spitfires (and many other models) that have a DC