Headlight Switch Wire

[Howard]

I brought a new wiring loom for my `51 Plunger. The wiring diagram in the Haynes manual has the tail light wire going straight up to number "5" on the headlight switch, but this is the terminal that has the brass metal strip and has a nut on top of the terminal which is diferent than all the other terminal points. Is this correct ? if so I guess I mount the wire with an "eye terminal". Am I right to do this ?

[Triton Thrasher]

I remember one wire does go there. I think it's so the tail light is on with head or pilot, but pilot goes out when head is switched on.

[terryk]

is your headlight switch an after market one or original they are different in some cases.

[Howard]

Hi Terry, I have brought an after market switch however the wiring diagram shows it as being the same set up as the orig.

[bsa-bill]

Don't wont to second guess what Terry means but maybe he is alluding to some of the after market switches being minus the copper strip that provides voltage to the central stem of the switch, this threw me for a while as it means it wont work as Thrasher points out

[Mosin]

I remember looking at aftermarket headlamp switches at Stafford show last year and being struck by the fact that there were several different designs/configurations of pins available which all looked exactly the same from the switch side. Add to this the confusions presented by an aftermarket loom and the confusions just increase.

My advice would be to throw away your existing wiring diagram as it will only lead to confusion and frustration and, armed with a multimeter, stick to basic logic. You know that the first switch position should turn the pilot light, instrument light and tail light on. Therefore look at the switch to see which terminals need to be connected in order to make this (and nothing else) happen. Use your meter to identify which of the wires coming off the loom are connected to these lamps and connect them accordingly. Repeat the process for the other switch positions, remembering that you want the pilot light to go off when the headlamp bulb is on either dipped or main beam. Ensure that brake and tail lamp are functioning correctly and before screwing the switch back into place take a photo of what you have done for future reference!

Warning though... There is a lot of current flowing through the ammeter connectors and it is VERY easy to accidentally touch these onto the headlamp casing when you are fitting/removing the switch causing a violent short and lots of sparks. It's just one of the perils of working with a live circuit!

[iansoady]

My advice would be to throw away your existing wiring diagram as it will only lead to confusion and frustration and, armed with a multimeter, stick to basic logic. You know that the first switch position should turn the pilot light, instrument light and tail light on. Therefore look at the switch to see which terminals need to be connected in order to make this (and nothing else) happen.......

I agree. It's useful to make up a set of truth tables (positions 1 - n across the top and down the side) then systematically check each pair for continuity in each switch position. It's the only reliable way of knowing what the switch is doing.

[Gavin]

Hi Mate, I think I have done a similar journey to yourself... Bought a loom for a 51 plunger and eventually worked out (I suspect) that it is for a Swinging arm frame. So I have one extra red live wire at my headlight / switch area... so I finally isolated that one. I also worked out that I had purchased a replica switch which is different to the original.... I have now re installed the original switch, and the whole system has never worked better.

One more final improvement... I had the lever the wrong way round.... I should get an award for the most mistakes possible... But I must add I still them being offered on Ebay with the lever pointing the wrong way.