wiring - tail light and switch

I'm in the final stages of rebuilding a 1970 roadster that I purchased not going, and without an ignition switch. I have installed a new harness and ignition switch into the side cover. I have been blissfully ignorant of electricity until now, and have spent hours (days actually) looking at the wiring diagram trying to figure it out, and connect everything.

I am almost there. One issue that I have (out of several still to resolve) is the rear tail light/brake light. The switch on the head light has three positions; left the tail light is off; centre and right it is on. That accords with the positions shown on the diagram.

What confuses me is that the switch on the sidecover (that I bought from Andover, so it should be the right one) seems also to directly control the tail light. It seems to have 3 positions; if it is off, the tail light doesn't work; if it is half way (and that is not a clear click into position; more a kind of "feel it in and it will stay there") the tail light can be controlled by the switch on the headlight; but if it is fully on, the tail light is on permanently. Is that how it should be, or have I stuffed up the connections?

Once this is figured out, I just need to establish why the brake light isn't working....

Thanks in anticipation.

I think that is the "parking" position which leaves the tail light on and lets you remove the key. A good way to run down a battery which is a good reason not to connect it

Jean

If you have a 1970 Commando it would have come with a two position key switch, off-run, and three spade connectors. It sounds as if you have a '71-'75 style switch which is a four position, park-off-run-lights. This may be causing you confusion when looking at the wiring diagram for a '70 as the later switch has the position for the "park" light that was simply controlled by the headlight toggle which was a three position switch on the '70 while the later models used a two position toggle.
The late style switch will work fine, you just have more options in wiring it.

Ron, the switch that I have has 4 spade connectors (two groups of two; I have assumed that two are on one side of the circuit, and two on the other) so presumably that makes it the later model switch. So I guess I can leave it as it is, or play around with the connectors in to the switch to see if that makes a difference. Presumably one position makes one outgoing connector live, and another makes both live.

I had assumed my switch has two connectors for incoming wires - of which one is redundant - and two for outgoing wires.

But I infer from your email that with three "on" positions, there should be three live outgoing spade connectors? I'll get out my little tester with the light bulb and figure it out.

I seem to remember that there are several sorts of 'later' switches. Those originally fitted to Nortons had a separate feed for the rear light in the park position but Triumph switches which looked similar didn't, relying on a diode I think to prevent the ignition circuit being live when the park lights were on.

I received the wrong one once. I do remember that it was in a Lucas box and came with a small slip of paper showing the diode installation. It puzzled the hell out of me at the time. If you don't want to have a park facility, it's not a problem.

Chris T said:

Ron, the switch that I have has 4 spade connectors (two groups of two; I have assumed that two are on one side of the circuit, and two on the other) so presumably that makes it the later model switch.

Click to expand...

How many key positions does the switch have?

As it sounds like you have a two position ignition switch, if it only has two pairs of common terminals?

A four position switch would have either three common terminal spade pairs and one single spade, or four common pairs of spades? These switches therefore have four independent terminal positions (either single or double spades).

However, the '71-('74) wiring diagram only shows three sets of terminals (1,2,3) so that particular switch may be different?

79x100 said:

I seem to remember that there are several sorts of 'later' switches. Those originally fitted to Nortons had a separate feed for the rear light in the park position but Triumph switches which looked similar didn't, relying on a diode I think to prevent the ignition circuit being live when the park lights were on.

Click to expand...

Harris Bonnevilles (and maybe the very late Meriden Bonnevilles?) had the ignition switch with the additional diode, I think?

A picture of the back of the switch would help a lot here.

L.A.B. said:

Harris Bonnevilles (and maybe the very late Meriden Bonnevilles?) had the ignition switch with the additional diode, I think?

Click to expand...

I'm proud to say that I have only a limited knowledge of Triumphs :wink:

My comment was based simply on what Al Osborne told me at the time (or my recollection of it which may not be the same thing at all !)

The pre-71 wiring diagram has a 2 position ignition switch and a 2 position light switch. I looks as if the light switch should work whatever the position of the ignition switch.

You can't really tell how a switch operates by looking at the physical layout of the connections. I would make up a dummy circuit out of bits of wire, a battery and lamp (take a torch to bits) and try all the switch positions until you are happy what is going on.

Ron, the switch that I have has 4 spade connectors (two groups of two;

Click to expand...

Chris, the original early switch had three spade connectors, one feed and two switched. I have discovered that many of the replacement switches have two groups of two such as yours.

It seems you have the correct switch, but are probably stopping the key between postions. This switch does not have very distinct detents like the later style. It should be turned fully one way or the other.

Your brake light should have a feed directly from the switched side of the keyswitch (typically a white wire) to the stop lamp switch and a brown wire from the other side of the switch to the brown brake light wire on the lamp. These models did not come with a front brake light switch, but many have a cable installed with a switch built in. This requires another white wire from the keyswitch to the cable switch and a brown wire to connect to the brown wire from the rear brake pedal switch or at the rear lamp.

I solved the problem with the wiring of the rear light. It transpires that the ignition switch that I have is the correct two position - on/off switch for the 1970 machine; the reason why the rear light came on independently of the head light switch was because it was not the tail light, but the brake light. One or both of the switches for the front and rear brake was open, and the tail light was operating as it should. Wiring now completed, and now working as it should - at least with the bike standing still...

I thought that I should post a further message to update this issue, now that I have solved the problem of why the rear light was permanantly on, when the ignition switch was on. The ignition switch that I have turns out to be the simple two position switch. When I turned it on, the rear light came on - at least I thought it was the rear light; turns out that it was the brake light; the rear brake cable was loose enough for the rear brake switch not to be in the "off" position, and so as soon as the circuit was live, the rear brake light was on. So everything was as it should have been... now I have to figure out why the horn was working until I bolted everything up, and now isn't...