Maybe it's old news to the old-hands on this list, but here's one that has
me feeling extra humble this evening.
I had (HAD!) a puzzling electrical problem with my 69 2000: no
directionals, temp or fuel gauge, and (as I discovered late in the game) no
backup lights either. I did get very brief (15 sec.) intermittent readings
on the gauges, and on nothing else, before all these would go dead again.
Based on the wiring diagram that Ross (Sports Imports) has up on his Tech
Tips pages, this configuration of faults pretty much identifies the
problematic circuit. So, I began tracing the relevant line out of the fuse
box looking for the break. Of course, I first checked all the fuses and
their connections to confirm power there. I checked the under-dash v-reg.
Numerous hours (over several days) later, including time to bug and rebug
some friends on the list -- both Paul Kort of OROC fame and Tom W. of
universal Roadster fame were ready to pour over their wiring diagrams to
help -- I learned only one new fact: My tolerance for lying on my back,
head under the dash, feet up on the driver's seat, has sunk to an all-time
low. 30 minutes of that and I'm incapable of focusing on anything but a
In desperation, and in a last effort to avoid pulling apart the radio
console to get at yet more wiring, I tried the following. Since it was
sinking in that I had what Paul refers to as a "hot short" in a line --
where the line fails under load but not otherwise -- I tried this "trick,"
one that I recalled from years ago in my Spitfire days -- with LUCAS
electrics design, you learn all the tricks!
I waited until night and turned out the lights in the garage. I started up
and watched for a spark, where the "hot short" might be. Even if it is
inside a sheathed wire, sometimes you can spot the spark through the
Lucky for me it was quite visible: It was in the fuse itself! Yes, there
is a hairline fracture in the metal strip in this particular fuse which
acts like a thermal switch: the fuse tests "on" under a light load, e.g.
continuity is there when the power is off ; but the fuse is "off" when you
are looking elsewhere for the problem!!
So, before you succumb to disassembling your dash searching for a bad
connection, try looking with the lights out!
Oh, one last point. I learned the hard way that, though it appears to be
"stock," my fuse box is NOT configured according to (any of!) the wiring
diagrams on the WEB. The circuits that connect the respective components
are as depicted in the diagrams, but their positions in the fuse box do not
match the diagrams. If you haven't done so already, when you have 15
mintues to spare, take a pad and pencil and determine exactly what each of
your fuses controls! Do this both with the engine running and with the
ignition in the "accessories" position. It may save you much more than 1/4
hour if ever you go to trace a faulty circuit.
Best to all, and to all a good (dark!) night,