Hi everyone,
Noting the interest that there has been on wiring
harnesses in recent times maybe the following is of interest.
Fault Finding:
When trying to find the function of a wire that you
cannot find a home for the usual test is to see if it has 12 volts
on it.
Beware of using digital hand held meters, they are designed
for work in modern low current electronic testing and they draw very
little current from the circuit under test ( a few micro amps) and they
can give misleading results because of this. When using one of these
meters it is quite possible to find 12v on a wire that should in reality be
connected to chassis but because of the low current drawn by the
meter the in circuit resistance does not provide enough voltage drop
to give you the correct indication that it is really a chassis connection.
Application of Ohms law will demonstrate this.
Electrical testing is much better and cheaper done with 12v 6 watt lamp
with test wires soldered to the connections. The results will be much
more meaningful.
Electrical Connections:
If you have to modify the wiring and add a new
terminal to a wire try and use a good quality crimp terminal from a
branded manufacturer like AMP. There are many cheap imported
terminals around that do not form a long term reliable connection.
Take care stripping the insulation not to nick the conductors which
will ultimately fail and use a good quality crimp tool that performs
both the connection and insulation crimp in one go. Do not use
side cutters for crimping terminals and DO NOT be tempted to
then solder the connection for 'belt and braces'. The solder will
wick up the wire under the insulation and the wire will ultimately fail at
that point in the future.
If you want to improve the reliability of a crimp connection then heat
shrink some
adhesive lined heat shrink sleeving over the wire terminal area. This is
particularly useful around the hot oily areas in the engine bay and can be
obtained from electronic shops such as Radio Shack and shrunk using
a hot air paint stripping gun.
Insulation and Wire:
Any additional wiring that has to be added to the loom
should be done in automotive quality wire and secured to other loom wires by
Ty-Raps or by binding it in with PVC Loom Tape (non adhesive PVC tape as
used on later original looms).
Some up market cars use higher quality wire made by Raychem and if obtainable
this is to be preferred as it has better abrasion resistance and high
temperature
characteristics than conventional PVC.
Best Regards
John Dowson
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