First of all, don't try anything until you have a wiring diagram to tell you
what's what. There should be one (for a UK MkIII I think, don't know how
different the US MkIII is) at
http://www.totallytriumph.net/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=1
09&forum=DCForumID5 but the picture doesn't show up for me - if it doesn't
work for you let me know and I'll ask the creator (who knows me well enough
by now) to fix it or e-mail me a copy I can forward to you.
Next, you'll need a tester. A multimeter (digital or analogue, but I
personally find my analogue one easier to use) is ideal, but you can usually
get by with that device that looks much like a screwdriver with a pointy end
and a wire that you connect to ground, that lights up when the end touches a
live.
After that, you just need a methodical approach. Test something. If it
doesn't work, see if there is electricity reaching the device. If not, head
back to the switch and see firstly if electricity is reaching the switch,
then if the switch is successfully sending electricity back out again when
it is switched on. If necessary, then head back to the fuse box and all the
way back to the battery to find the last point where you do have
electricity.
One tip - sometimes you may appear to have electricity, but the device
(which has nothing wrong with it) doesn't work. This means that you have a
poor connection somewhere along the line - there is just enough connection
to carry the tiny current required by the meter, but not nearly enough to
power the application. This can often be a problem with the switch, if
corrosion builds up on the contacts.
Another cause of the above symptom (electricity present but device doesn't
work) is a poor ground - the electricity gets into the device, but has no
way back out, into the frame and back to the battery. If you ever see a car
that is trying to indicate, but instead their brake light flashes dimly,
this is a poor earth at the rear lights (the brake light bulb provides an
alternative route to earth in the absence of a decent earth).
Fuses can cause mysterious issues too - if there is corrosion on the clips
and/or fuses, or if the clips are not gripping the fuse firmly, this can
again appear to pass enough current to fire up the multimeter but not enough
to power an application. Probably best in this case to clean the fuses and
clips, and make sure the clips are tight, before you start to test anything
at all.
You do not need to have the engine running to test any of the electrics,
although most circuits (excluding lights, interior lights, cigarette
lighter, and horn) will require the ignition to be on. If you take several
hours over this without running the engine inbetween, you may have to
re-charge the battery a little afterwards (or during).
I hope some of this helps you!
Richard Gosling
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