You can use the brown at the fusebox as a source, but coming up from the
solenoid will give very slightly less volt-drop if you use a heavy gauge
wire.
You need to be careful with fusing. If you put fuses or 'circuit breakers' in
the existing blue/white and blue/red wires then they will only be protecting
the wiring from the fuses to the relay windings. Unless you cut in to the
wiring by the dip-switch and put them there they won't by doing anything
useful if put immediately before the relays, for example, and they won't be
protecting any of the circuit from the 12v supply (fusebox or solenoid brown
wires) through the relay contacts and out to the headlamps themselves. You
can put a large capacity fuse (fusible link) in the feed to the relay contacts
to protect against shorts in the wiring to the headlights, but similarly it
must be as close as possible to the supply. And then you have the situation
where a fault on a single headlight will blow that fusible link and you will
lose both main and dipped beams.
I strongly recommend fitting individual *filament* fuses i.e. four altogether,
connected to the output of the relay contacts. They will protect the wiring
from there to the headlamps themselves, and also limit the loss of
illumination in the event of a fault to one beam on one headlamp in all but
extreme circumstances. These fuses should be double the current taken by the
current of one main beam. You can fit a main fusible link as well, but this
should be a minimum of four times any one filament fuse, and will only be
protecting a relatively short piece of wiring, especially if you pick up the
12v supply from the fusebox.
I parted the 4-way bullet connectors by the right-hand headlight and with a
volt-meter (or test-lamp) determined which of the blue/white and blue/red
wires came from the dip-switch, the others go to the left-hand headlamp. The
two dip-switch wires I wired through two new 2-way bullet connectors back to
the relays mounted in front of the existing relays, the output of the relays
went to four fuses mounted just behind the radiator mounting panel, and two
blue/whites and two blue/reds from the output of the fuses to four more 2-way
bullet connectors by the right-hand headlight one pair feeding that and the
other the left-hand. This avoids cutting into any wiring, and allows things
to be restored to original if anyone wants to.
Have a look at http://www.mgb-stuff.org.uk/wn_electricsframe.htm, click on
'Lighting' and 'Uprated Headlamps ...'.
PaulH.
----- Original Message -----
Does anyone have any other suggestions that might work better?
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