I didn't realise you couldn't get single mini fuse holder,
I'm not sure you can't, I've just never looked. I've pretty-much always used Vehicle Wiring Products
, they don't sell 'em the cars have mini-blades, it's a pita keeping track of loose ones so I use ordinary blades on the bikes.
Up to you. I used relays on my T160's because I always intended fitting either 100W-main-beam or twin 60W-main-beams.However, I've fitted relays as a matter of course on any subsequent rewire simply 'cos I think even with only a single 60W main (55W dip), with ageing standard switches and other wiring, it's a good idea; and, if I want to upgrade to 100W main-beam subsequently, it's just a simple bulb change. T160's have a relay for the starter as standard; I upgrade horns to twin Fiamms, but afaik all twin-horn installations have a relay.
have you a link to relays you use?
The front part of the T160 rear mudguard is plastic and incorporates an open-topped compartment originally for the tool roll. The sides of the compartment just perfectly-accommodate two interlocking relay sockets
back-to-back with the wires in the compartment. So I have a block of relays/bases under the seat, detachable from the harness with a multi-pin connector
Otoh, the T100 doesn't have that compartment (unless I fit it with a T160's 2-piece rear mudguard), but the two headlamp relays fit inside the headlamp shell and the horns relay is mounted on the frame bracket under the tank that originally took the horn itself.
On this bike, I've connected the wiring to the relays with "Trailing Relay Sockets"
Why didn't they use relays originally,
They did. Indicators use a relay (Lucas 8FL); twin horns on '69 and '70 Lightnings and Bonnevilles, and '69-'74 triples, had a relay (Lucas 6RA); T160 original points ignition had 6V coils fed through a ballast resistor; a starter-button operated relay (Lucas 22RA) operates the starter solenoid, and bypasses the ballast resistor to feed full battery Volts to the coils just for starting.
However, apart from some Commandos, all the British bike makers used the shonky Lucas BPF headlamp bulbs, which were variously 50/40 or 45/35 (or 45/40?), none of which draw more than ~4A so, at best, relays would've been an unjustifiable extra cost when the bike makers paid Lucas as little as possible.
Btw, if you do a Forum Search for "relay", you'll find some contributors also use a relay to supply electronic ignition, in theory taking the load off the handlebar kill switch. In practice, any ignition coil(s) only draw(s) a similar ~3.5A to a 40W headlamp dip beam; if the kill switch is dodgy, it's still in the supply to a relay, so it'll still affect the ignition. I prefer to fix the kill switch and forego the relay.
If you have a diagram for relays that would be helpful. I guess it will just be headlight/rear light, and horn.
Mmmm ... at its most basic, a relay is simply a remote on/off switch, that you operate with another on/off switch; all you're doing is taking away the Amps of, say, an electric-starter, 100W-main-beam, etc. so the hand-operated on/off switch and its wiring can be small and light. As the rear light or single standard horn are very small loads (~0.5A and ~2A respectively), imho relays for them become an added complication without any benefit.
Otoh, particularly twin accessory horns major on being LOUD
so more Amps each, doubled, without a relay, through the standard handlebar button's tiny contact area risks welding the contacts together.
So a relay for them.
With a more-powerful headlamp, depends how you want to do it. I prefer to keep the standard principle, of the dipswitch switching off one headlamp bulb filament when switching on the other. So I use two basic on/off relays, like the linked one with the fuse, one relay for main and one for dip. Then the dipswitch switches the relays, not the headlamp; each headlamp filament is connected to a relay, along with the battery.
Decide where you want to site the relays and if you want to use one or other of the sockets I linked.
If you look at the relay link again
, you'll see a circuit diagram as one of the images; the terminal numbers will be moulded into the relay too:-
. 85 and 86 are the 'low-power' terminals; the 'oblong-with-slash' in between is the electro-magnet operated when the terminals are energised.
. As you've upgraded your bike's headlamp, you know the bulb main and dip wires are connected to the corresponding wires from the dipswitch (with bullet terminals and snap connectors?).
. Disconnect the headlamp from the dipswitch at those connections; connect each dipswitch wire with a new wire 'n' terminal to either 85 or 86 on one relay each; these then become respectively the 'main relay' and 'dip relay'. Connect the other of the 85/86 terminals on each relay to the bike's (Red?) 'earth' wires network.
. Also with new wires 'n' terminals, connect the headlamp main and dip wires to terminal 87 on the corresponding 'main' and 'dip relays.
. On my T160's, the relays' terminal 30 are connected directly to battery -ve with "28/0.30" wire
(28 strands, each 0.3 mm. dia., 'thinwall' insulation, rated for 25A) through a 15A fuse (100W main is 8-and-a-bit Amps, 55W dip is ~4.5A, I might flash main when dip is on).
. Otoh, the T100 has the later version of the Lucas on/off ignition switch, with two double-spade terminals riveted to the back:-
.. As I don't go in for the 'parking lights' malarkey, the lighting toggle switch supply wire is on the same double-spade as the White wires. So the Brown/White from the ammeter is on its own on the other double-spade.
.. As the Brown/White from the ammeter, and the Brown/Blue from the battery to the ammeter, are also 25A-rated 28/0.30 thinwall, I connected the headlamp relays' supply wire just to the unused terminal on the ignition switch. This means any headlamp supply from the battery indicates on the ammeter, rather than bypassing it, so the ammeter still gives a true
indication of charging or discharge of the battery.
Should I change my 15 main fuse for resetable
Up to you. I haven't used 'em because in the back of my mind is they have a finite life (1000 switches?), might not be a problem now but, when I did my first rewire thirty-five years ago, I didn't want the problem that, if it wouldn't reset years later, was there still a short or had the resettable reached the end of its life (when I'd be stuck without a fuse
). Maybe I'll carry a resettable as the spare?