Help with ignition switch please!

Hi all,

I have been watch the site for a while now but now is my time to join and ask for some help so please can you help me with a couple of questions about the ignition switch!

My battery has just started to go flat after standing for 2 or 3 days. The battery is not very old and it has only just strated to happen so I suspect I have got some “leakage” to earth when switched off.

I have started by checking the ignition switch and wonder if there is a small current flow when the switch is off so question 1 is can you test the ignition switch by measuring resistance across the various terminals?

The second question is about the wiring. I have a Lucas ignition switch which I think is original (1974 850cc) and when I slid the rubber cover off, two of the terminal became disconnected and I am not sure where they go (one with 2 brown/blue wires and the other with 2 brown /green wires). The other 2 terminals stayed on with a single yellow/blue wire being attached to the only connection on the switch with only one terminal whilst the other connection was on the next connect clockwise looking at the terminals. I am sorry this is difficult to describe!!! Looking at my Haynes manual, I am not sure how to wire it back up! That says that the yellow/blue should be on terminal #4 and the whites should be on terminal #2. Now, according to the diagram these 2 terminals should be opposite and not next to each other as I found. I can simplify the question to how the heck do you wire up the switch!

Thanks for any help.

Keith56

There are a series of technical articles on the Old Britts website-oldbritts.com. Have a look at the one titled "Ignition switch and lock assembly, how they fit together". There is a photo of a switch showing where the wires connecrt
Cheers
Bazz

Hello Keith56,

Even though the battery isn't very old (you don't say how old?) it could still be faulty?

Does it still hold a charge when disconnected?

There's a possibility that a faulty Zener diode, rectifier or 2MC capacitor (if fitted) is causing the battery to discharge rapidly.

To check, charge up the battery and wire a 12V low wattage (tail light?) bulb between the battery Neg. terminal and the Brown/ Blue battery wire (or alternatively connect the Brown/Blue to the battery, remove the fuse and wire the bulb to the fuse holder contacts).

Does the bulb light up (or glow) with the ignition 'off'?

If NO, then the battery could be faulty.

If YES, then disconnect the wires each in turn (and re-connect before moving to the next one) from the Zener-rectifier-2MC.

If the bulb goes out when one of them is disconnected then that item is likely to be faulty.

If after doing that the bulb stays lit then the problem could be with the ignition switch so disconnect the Brown/Blue wire from the terminal and check if the light goes out?

The switch wires should be connected using the terminal numbers,-how it is drawn in the wiring diagram is not really important.

the easiest thing to troubleshoot is the ignition switch. im not positive mine is stock but if you have a mulitmeter with a continuity option, then try this out.

on a piece of paper draw the various terminals and their positions. attach one lead from your meter to one terminal position. with the key out of the switch, touch all the other terminals with your other lead and see if you get anything. if not, then good, and keep moving your first lead around and make sure you check all terminals. then keeping the first lead on that same first terminal, turn the key to ACC and touch each terminal with the other lead, and note your findings. then keeping it on acc move your first lead to another terminal and move the 2nd to each other terminal, writing down your findings.
switch the key to ign and do the same.

eventually you will be able to figure out which terminal is battery, which ones have continuity with the batt when the key is in ACC and which ones have continuity with the batt when in ign.

i believe on mine, i have a 2 prong term as battery, a 2 prong term as acc, a 1 prong term as acc, and a 2 prong term as ign.


i might have confused you with this post as well. i tend to do that. rambling on with no direction.

If it's the stock switch, you should find the connectivity is:

daytime running: 1-2
nighttime running 1-2-3-4
park 1-4

So with an ohm meter you can figure out which is which. #4 would be the only single, and they should be numbered sequentially in clockwise order looking at the back (or at least that's how the ones I've seen have been).

brown/blue goes is the battery/zener/2MC cap/rectifier. It goes on #1
white is -12 for the ignition etc. It goes on #2
brown/green is for the lights. It goes on #3
blue/yellow goes on #4 and runs to the switch in the headlight shell, supplying power for the pilot light and headlight.

All, of course, assuming you have the stock wiring and Lucas switch (it sounds like you do).

hth,
Debby

Thanks to Bazz, LAB, Driggs and Debby. Given me lots of clues to work on here so thanks!

keith56

Excellent response Deb.

I would replace the switch. Norton ignition switches are known for harboring gremlins that cause intermittent problems.