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Headlight switch wiring diagram? Series III

Chicken Drumstick

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Does anyone have a picture showing what terminals on the back of a Series III headlight switch should go to what?

Not my switch, just borrowed from Google:


Having issues with the rear lights (not brake or indicator, just rear lights). They did work fine and were fine for years prior.

Using the pic above, the red wire terminal at the top, activates on stage 1 of the switch, i.e. sidelight position, these are wired into the dash lights on mine.

The next terminal down on the bit that sticks out the back, this wire is permanent live going into the switch.

Next terminal down on the back, has no wires in this pic, but comes live with switch in sidelight stage 1 position.

Then the two wires at the bottom are the front sidelights and headlights (forget which). But one comes on in position 1, the other position 2.

On mine, that 3rd terminal down was also blank with no wire coming off of it - should it have been?

I had to repair the rear of the loom due to an off roading incident, but I think that is coincidence. I ran new wires from the front of the seat box, down to the rear of the vehicle for the indicators, brake lights and rear lights. The loom from the seat box up into the engine bay was intact however.

That said, when I pulled the dash front forwards to investigate the rear lights, I couldn't see any wire for the rear lights, so I extended the new wire from under the set box, right up in the dash and hooked it up to the 3rd terminal down (the blank one), as it came on with the switch in the sidelight position. This has worked for a week. No idea if it was correct or not, but could find no trace of another wire in the dash for the rear lights.

Tonight the rear lights have stopped working again. That 'blank' terminal still has the wire attached, but never becomes live any longer. The rear lights work if I unplug the dash lights and plug the wire in there instead. So I don't know if it's damaged the switch plugging them in there, or something else.

Any ideas?

As in, where should the rear lights have actually been be wired in originally to the switch?

What is that blank terminal for?

Why did the blank terminal stop working in under a week?


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According to the wiring diagram, main power comes from the unfused side of Fuse 1, via big brown wire to terminal 4 of the switch.

Tail lights are fed via the red/black trace wire from terminal 1 on the switch, which also feeds the panel light switch next to it - a switch I've always felt redundant seeing as I never turn mine off....if you need to drive with sidelights on, then you need your dash lights on!

Series 3 Neg. Earth

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Pass. I think my switch is on it's way out. Sometimes it doesn't click over onto the second stage...waggling it backwards and forwards eventually gets it to click over. I've got a spare just in case, have taken to carrying it now, as I finish work at midnight so I kinda need the headlights!

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  • 2 weeks later...

Worth throwing a fuse in-circuit while you're faffing with it, very early ownership experience of the 109 was the rear loom combusting :blink:

Thats still on my list. For my a big + goes from battery to killswitch in dash and on to starter motor (very loose connection there), from starter + back up in the dash.

That (believe brown) wire back up in the dash I'd like to fuse with ~30Amps, just to prevent fire.

Does anyone know the power drawn by the starter? I might also fuse the + near the battery before the killswitch...... or isn't that usefull?

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According to the wiring diagram, main power comes from the unfused side of Fuse 1, via big brown wire to terminal 4 of the switch.

That's what I've noticed and reported in a earlier post somewhere (will try and look it up), that headlights (main beam and dipped beam, not day lights) are unfused!


see my one man rant from post #25 and on :P

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