Like most people, the switches in my MGB didn't work so well. There are a
couple related reasons for this. First off, the switches are, well, just
old! Oxidation, dirt, heat, and pitting (from arcing) have contributed to
this problem. While replacement switches aren't terribly expensive, it is
possible to rebuild them in many cases.
After very carefully dis-assembling them, I cleaned them out with a mild
degreaser, and polished the internal contacts. Reassembling them with a
proper lubricant, or at least with some di-electric grease, restored them to
a smooth operation with a very low electrical resistance (more on this
later).
The interesting point to note is that after talking with some other people,
it seems that nobody took the additional steps needed to truly solve the
problem. Most just bought new switches and plugged them in. The reason this
is a problem is because of resistance, namely, the terminals on the wires
that mate with the spade lugs on the switch. The wiping action of the
contacts is simply not enough to overcome 20 - 30 years of oxidation and
related scum build-up. So what you essentially wind up with is a relatively
high resistance connection at the switch. Running current through a resistor
(or a bad connection) generates HEAT, which will burn up your new or
repaired switch. I suspect that caused a lot of the problems in the first
place. If your light switch feels warm or hot after the lights have been on
for a few minutes, you have a problem! This will destroy your switch, wires,
and connectors! Just remember, that POWER = CURRENT x RESISTANCE (P=IxE).
The dirtier your connection, the higher your resistance, thus the more heat
generated at that point!
So what to do? I guess that depends on your level of ambition. Don't neglect
to (gently) polish the spade terminals on your switches. Bright and shiny is
good. But the problem is those dirty, abused connectors that you're about to
plug back into your switch! The best solution is to cut them off and crimp
new ones on. Use high quality insulated terminals. Depending on the severity
of the past problem, the wire may be black and discolored inside the
insulation for an inch or more beyond the wire end. If your wire isn't
bright and shiny where you crimp on a new terminal, you have not solved your
problem. Being that there is only just so much slack, you may need to try to
make do, so carefully clean the end of the wire with emory cloth before
crimping the new terminal on. I recommend the use of di-electric grease on
the terminals to prevent future oxidation. Perhaps put a small amount on the
wire before you insert it into the terminal.
The cheesy method would be to take a thin ignition file and clean up the
terminal carefully. You may need to close the terminal up a little bit to
improve the connection - it should be snug, but not require undue force to
install. Realize that if the wire is under the crimp of the terminal is
blackened, you haven't solved anything!
I have also considered putting a small capacitor across the switch to
eliminate arcing when the load is switched on/off, but that may be serious
overkill. Another solution, not for purists though, is to install a relay
under the bonnet, and use the dash switch to drive the very low current
relay. I suspect this may be the overall best solution, especially if your
wiring is really bad. The small coil on a relay will be much more tolerant
of a high resistance switch circuit that the headlamps themselves would be.
I'll bet your lights would be a lot brighter this way!
--
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Marc Siegel, ABSnet Internet Services eMail: smarc@abs.net
Baltimore, MD http://www.abs.net voice: 410/361-8160
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