REWIRING YOUR BRITBIKE (2-WIRE ALTERNATOR) - THE 22-WIRE LOOM
- by Pete Snidal, (C)2001
Is your wiring harness a mess? Weird assortments of wires,
different colours spliced to different other colours,
half-dissolved electrical tape streaming in the wind?
And where did all those wires come from, anyway? Time
for a change? You can build yourself a new wiring harness
for less than the price of a case of beer, and an afternoon's
satisfying work. Here's how:
First, a word on your rectifier and a capacitor. If you're
still using the Lucas selenium rectifier (the mess of square
fins under the seat beside the battery, you'd be well advised
to replace it with a more modern solid-state bridge rectifier.
Radio Shack, or any electronic supply house, will sell you
one for less than a 10 spot. Rating must be min 20 Volts and
10A DC. Be sure to get the one with the spade terminals.
You'll want to mount it on a piece of metal that will dissipate
the heat it generates doing its job - you can use your rear
fender, but I generally mount it on a piece of Aluminum of
about 20 square inches, such as 4 X 5 inches. Be sure to
mount it in the best way you can for heat conduction.
You may elect to put in a capacitor as well - they usually
make it possible to start with a dead battery, and generally
smooth things out down there. Once again, you want 20V rating,
and one about 4" long and 1 1/2" wide - the capacity of these
things varies with the size, and that's about the right size.
While you're at the eletronics supply store, pick up some "shrink
tubing." This is heat-morphing plastic tubing which you will use
to cover any splices you may make - since you'll be using all
new wire, the only ones you should be making will be on the
alternator wires to reach your rectifier, and this is only a maybe -
your present wires may be long enough. If you are forced
to make any splices, be sure to solder them if at all possible.
(You'll also likely have to splice your tail and brake light
wires.)
If you're building a new loom, be sure to do it in two stages,
the first is connecting the various parts together. Cut and
fit the wires so that they'll be the correct length when loomed
(taped together). You may find it helpful to temporarily wrap
with a single turn of tape here and there as you go.
When you've finished this, you'll have only 3 wires running under
your gas tank, and 3 running to your rear light from under the
seat. A siamese pair from under the seat to the stoplight, and
a pair running down the frame to the points.
PARK LIGHT
The stock Brit parking light was a second small bulb in the
headlight reflector. If you or some DPO has gone to a sealed
beam headlamp, you may want to mount a clear bullet-style clearance
lamp under your headlamp - if there's a Zener in the way, you
can mount it below the Zener.
TOOLS AND MATERIALS
A pair of side cutters, a connector crimper, and a selection of
spade and ring connectors. I generally bend the wire in a loop
and tin rather than use ring connectors. You'll also need a
selection of #14 and #16 automotive stranded wire, and a 2 foot
piece of black siamese lamp cord from your local hardware store.
With the usual screwdrivers, wrenches, etc., you're in business.
1. CHARGING SYSTEM - 6 wires
2 AC wires from alternator to rectifier. Ground + DC output
rectifier wire to chassis and to battery + through a 10A fuse.
Be sure rectifier is heat-sinked to a suitable spot. Run a (-) (hot)
wire from rectifier through a second 10 fuse to ammeter, fuse close
to rectifier. Connect also 3 more black wires to the same
ammeter terminal, one goes to light switch input, one to ignition
switch, and one to the Zener Diode ungrounded terminal. Now run another
black wire back from other side of ammeter to battery hot (-).
All wires +14 stranded. + wires black, - wires red.
2. STOPLIGHT CIRCUIT - 2 wires
One conductor of siamese lampcord wire to each side of stoplight
switch. Run lampcord up frame member to rectifier. Connect one
conductor to rectifier output ( -) terminal, on the alternator side
of the fuse. Run other back to stoplight wire - this will be the one
that lights brightest when test-jumped to the battery (-) with
battery (+) test-jumped to chassis.
3. LIGHTS - 6 wires
Dip switch input to light switch (headlights out.) High and low
dip switch outputs to high and low beam of headlight connector.
HC ground to battery + (red wire.) - ground this wire to inside
of headlight shell on the way out, and also to the Zener case.
Run a black wire from the light switch tailight/park lite output
to the taillight wire - the less bright of the two.
Which light switch terminal is which?
* One more to
park light - these can be #16 wire, some colour other than red
or black is preferable. Ground the taillight by connecting its
case to the battery (+) with a red wire.
4. IGNITION - 6 wires
#16 wire from ignition output to both coils (-) terminals. Each
coil + terminal to a pair of points. Each also to a capacitor in
the capacitor pack. Ground the other side of each capacitor.
5. ENRICHMENT - 2 wires
A capacitor in the charging system would be nice - (+) terminal
to ground, (-) terminal to rectifier output.
6. CHECK
Turn on park lights and see if they work - in headlight and tailight.
Check brakelight. Ammeter should move towards discharge in each case.
If it moves in the wrong direction, remove the battery ground fuse and
reverse the ammeter connections. Replace the fuse. Turn on the
ignition and try starting the bike or check for spark with plugs out.
If any of these fails to work properly, check the circuit from
battery throught the appropriate switch to the appliance in question,
and back.
7. LOOM
Wrap all wires from headlight to tailight with electrical tape.
Strap to frame with snap ties.
There! Now you've gone and done it! You've rewired your bike,
with nice fresh proper-sized wires, no splices, ready for another
40 years! I hope you're proud of yourself!
* Finding the proper terminals on the light switch: One terminal is
the input terminal. There will also be a headlight ouptut terminal,
and a taillight terminal, and a park light terminal. You may have to
experiment to find how the internal switch connectons go. The Connections
will be as follows:
- Off - No connections between terminals
- Park - the taillight and park light terminals will
be connected to
the input terminal.
- Head - the taillight and headlight terminals will
be connected to
the input terminal.
It's an interesting exercise in logic - get a kid to help you figure it
out with your ohmeter or a circuit tester.
