wiring conundrum

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dunk 1
Posts: 208
Joined: 25 Oct 2007 18:16
Location: cumbria

wiring conundrum

Post by dunk 1 »

Hello - wondered if someone could suggest a reason for the following- have put on the wiring harness I made and connected it up to a battery yesterday. Generally it works fine, new front brake switch etc - I haven't tested the ignition circuit yet as no fuel tank. As part of what I was doing I wanted to reinstate the idiot lights which have never worked, had to leave one as the bulb holder is broken but wired in the high beam and general lights (red one). Followed the early wiring diagram for this part as even though it is electric start 79 does not have some of the bits on the later diagram.
When checking I noticed that when the switch was on low beam I had a very faint light in the high beam and red idiot lights and nothing when on high beam. Assuming I had managed to reverse something I cursed a bit and started to look round - then realised I had simply not connected the earth from the idiot lights. Did this and they worked perfectly - red light to show lights on - high beam when high beam on and no low glow when on low beam.
So where was the electricity coming from the first time for the weak glow. where did it go once I had earthed it and how were they working with no earth?
Do I need to even resolve this bearing in mind it worked fine once earthed and I would never have known if I had not missed this first time.
I presume any issues are going to be in the left hand bar switch which am going to have to dis assemble anyway as the rocker switch for the horn was in a very poor state and on assembly the horn is stuck on - I will try to sort it but I think the switch is past it - don't suppose anyone has a replacement lying round.
Any inputs welcome - thanks - Duncan
dunk
MickeyMoto
Posts: 2415
Joined: 22 Nov 2008 17:41
Location: Even further oop North

Re: wiring conundrum

Post by MickeyMoto »

Ah, electrickery! Lots of paths for the current to flow to earth via different bulbs...

I did the same when I rewired my Sport. I noticed the flapping plethora of blue wires by the headstock!
julianharty
Posts: 478
Joined: 15 May 2016 16:34
Location: High Wycombe
Location: High Wycombe Area (Bucks)

Re: wiring conundrum

Post by julianharty »

The bulbs would have been connected in series where one end was connected to the +ve and eventually there was a return path via one or more electrical components (probably another bulb) to the -ve of the battery. The effects of going through another component means they sort of 'split' the power (something called Ohm's law can be used to calculate how much the bulb would get once you investigate what else was in the return circuit). This split meant that the high beam was getting some of the power but not much so the filament was dim, whereas the idiot light got more and therefore was brighter. You might not be aware that some of the power is lost in the wiring and connections anyway, again the actual amount can be measured and/or calculated. Broadly, thicker wires and cleaner connections reduce that loss by reducing the resistance of these bits and pieces.

Providing the return (known as an earth) connection obviates the long path, electricity is lazy and takes the shortest path home (that's not strictly true in all circumstances but hopefully will do in terms of understanding the concepts).

I'm about to start the wiring of my Kanguro and will be dealing with lots of these return paths, in part as I've had the frame, etc. power coated and don't necessarily want to use the connections via a bolt, washers, etc. through the frame back to the battery -ve.
MickeyMoto
Posts: 2415
Joined: 22 Nov 2008 17:41
Location: Even further oop North

Re: wiring conundrum

Post by MickeyMoto »

Good old Ivy Watts!
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