Rear lights electrickery


I’ve just spent 3 hours poking around with a multimeter trying to find the source of this problem.

Lights off = indicators and brake light work fine

Lights (side and/or main) on = disco lights. Put the brake light on and the rear lights go out, both indicators come on constant. Put the indicators on and you get an alternating rear light / all indicators (front and rear) disco sensation.

All I can say is, must have confused the hell out of anyone following me the day it went wrong!

Anyway, what I think I have worked out is that the rear light cluster earth and rear light wires seem to have become crossed / shorted out. It doesn’t appear to be in the rear light cluster itself as those cables all check out ok so it must be somewhere in the main loom (groan).

Just in case anyone has had a similar problem is there anywhere in particular that this is likely to have happened? I am despairing at the thought of having to strip the entire wiring loom to find the problem!

It’s also absolutely baltic in the garage at the moment so I’ve come in as me hands were starting to go blue!

Which bike? as many are similar? My bike is a Tonti big block so similar to All the 70’s bikes and most of the 80’s right up to the calis and Cali vintage.

What did YOU touch last prior to this happening?

Unlikely to be IN the loom but as you go along just LOOK , use a torch even in daylight any rubbing thro the outer layer of the loom is a dead giveaway.

Usual places for a short cct are, from back to front:-

  1. In the rear light cluster

  2. At the junctions right hand side rear underseat frame it goes thro the rear mudguard and often wears thro insulation and shorts out. There are bullet connectors here and the loom clips to the inside of the mudguard.

  3. a good look under the seat around Battery IF the battery has moved/leaked it can wear thro insulation causing a short and as the wires from the rear lights go through that area look for where they go through the frame ideal to rub away insulation.

  4. As it goes under the tank it goes along right hand side ALSO Under the tank right hand side there is a cluster of earths front end under the tank bung type fittings and the tank can rub as well as where the wires go thro the frame headstock to the head lamp

5)The back of the headlamp the 12 way/15 way clusters wet can get in and after years of no problems can always simply go.

6)Inside the headlamp the indicators and everything has connectors in there

7)The Lights switch itself can very rarely break internally if a bit of plastic comes away it causes a short, but very rare.

Before you go to any meter just take a gooood long look anrwhere the wires/loom can rub as it is most likely a short out and is usually visible.

On my bike it has been the rear mudguard OR headlamp area that has caused this sort of problem

Hope this helps buddy

Short circuit or poor earth as suggested above.I’d be tempted to take a look at the ignition switch too. The copper worn from the contacts over years can build up and short the ignition & park contacts.Have found it useful to remove/clean the fuses and then remove one at a time to see what (if any) each circuit is affected.Best of luckSteve

Almost certainly an earth problem, try running a temporary wire from the engine to the rear bulb holder see if it cures the problem. Just take a length of wire, bare the ends hold one end on the bare metal of the engine and touch the other onto the metal of the rear light unit - remove the glass and put it onto the edge of where the bulb fits. Also try the indicators if that don’t work.Check the earth to the headlight next, they can give problems,Try the big multi connectors under the tank (As GB says assuming it is a Tonti type)

Check the wiring on the underside of rear mugaurd as it could of rubbed on the tyre

or its a bad earth

Morning all, thanks for the suggestions.

Guzzibear - it’s a 2002 Cali EV (80th anniversary model). Your suggestion no 3 may be on the money, the last thing I had done was the rear mudguard painted so all the rear lights have been off in the last couple of months. It didn’t go wrong immediately after being put together but I may have put the cables in a position to get rubbed.

Don - I tried your suggestion last night, using a new earth everything works fine - so long as you do each light in isolation, as soon as the tail light was connected it all started to go pear shaped.

Got to do some proper work today unfortunately but will try to get a look at it again before the sun goes down.

Thatll be it in my experience before you even think abou a multimeter just look the wires on these bikes go thro the mudguard clipped to it then into battery area SO good chance the short is in that area. IF you can’t find it follow the wires to the first connector dis the tail light and use a new wire to reconnect it if it clears the fault it is in that section if not then it is back towards the headlamp.

Whenever I am tracing this type of fault I tend to disconnect the offending wire then with a long bit of new wire basically jump around the area.

The wires have bullet type connectors just after the tail lamp cluster then in the battery area and again after the headlamp, then the 15 way and headlamp and 12 way up to the switchgear.

Well, it’s not in the tail light and I can’t see anywhere where the loom has rubbed through so looks like I’ll be spending a little longer troubleshooting this one.

Got the tank off already so will look to taking the headlight out of the circuit next and then work my way around the various connectors (though visually they all look OK).

I hate electrical problems!

Have you isolated the wires to the rear lamp that are causing the problem and used a fly wire to byepass them from the various connectors, easier than getting out a meter and will show where the fault is…or isn’t.

I would guess if you took the rear mudguard off there is a wire crushed in there somewhere sooooo pulling the wires at the lamp and connecting a flying wire from somewhere in the battery area will prove THAT part, or not.

Sorry if it is a bit baisic but a bit difficult when doing fault finding by remote and not seeing the actual bikeguzzibear2013-01-20 18:45:39

Thanks for your help guzzibear - I’ve had the whole rear light assembly off the bike and on the workbench, tested every wire and there are no problems there. When it’s connected up to the bike the indicators and brake light work with the rear light disconnected and a new earth wire, using the existing earth wire doesn’t seem to work even though I can measure continuity through to the engine. When you connect up the yellow wire for the side light/rear light it all goes wrong!

Using a multimeter on the connectors coming off the loom the yellow wire that is supposed to feed the rear light is going to earth as well as the correct black earth wire so that is the starting point for my trouble shooting. I just need a bit of spare time whilst the sun is out so I can work through the possible problem areas methodically.

OK have you tried simply connecting say the brake light feed to the rear cluster …work the brake if the bulb works then the cluster is OK

When you connect up the yellow wire for the side light/rear light it all goes wrong!
Then the yellow wire has a break in it’s insulation.

using the existing earth wire doesn’t seem to work even though I can measure continuity through to the engine

The Earth WILL show continuity even with a broken insulation it will show earth return

IF the cluster is OK then find out where the yellow wire goes on the bike and disconnect it at the first bullet on mine you can isolate the rear cluster there are bullets just after it then another set of connectors the mudguard side of the battery box.

Make up a lead connect the black of the cluster to earth and a lead from the next along bullet to the yellow. IF it shorts the problem is further back if it doesnt the probem is at least isolated.

If good replace 2 new wires if not re connect org wires and I would go to the headlamp, dis the yellow and put the flying wire from the headlamp to the rear cluster, again if it clears it you have identified where the short is if it doesnt it is further back . not sure if the EV has the same 12way and 15 way block IF it does then diss the link wire in headlamp …same scenario

back after from thet it is dash or switchgear…

MY bet is still the yellow black caught and shorting out.

Some while ago I did some work on Annies Virago and when popping the side pods back on trapped a wire in the bracket , only nipped it but it was enough to blow a fuse.

I did exactly what i have described found it in under 30 mins mind you I could NOT see the actual break or rub it had literally nipped the insulation and caused a short… I figured it must have been something I had disturbed, then used the flying wire around the part on the cct affected, no fuse pop …

Here is a thought sometimes a faulty bulb can also do this i had that too and THAT took a bit of figuring I proved it was the rear cluster itself, but couln’t figure why and before I went looking for a replacement cluster I took out the bulbs and for some reason just replaced them on a whim and it sorted it…

Worth trying a new bulb in the back light in case that has gone funny and is giving a short circuit to earthDoes the cali have the connector for the rear lights etc on the left side like the older models? Check the connections in there.I had all sorts of odd things happening a while back when the headlight lost its earth connection. It was the handlebar switch block connector that had corroded and needed a good clean.

Did you take the bulbs out for this test? To a multimeter a cold lamp filament can look like a dead short because the resistance is very small. The resistance of a cold unlit bulb filament can be less than 1 tenth what it is when lit. E.g. 5W bulb suggests 5 / 12 = 0.41A, Ohms law 12 / 0.41 = 29 Ohms. But when cold unlit could be just 2 Ohms. A bit of oxidation on the meter probes and/or connectors you put them onto often also looks like 2 Ohms. The higher the power of the bulb, the more it looks like a dead short circuit…

PLEASE don’t anyone take these comments as a swipe at any expertise

One thing I was taught when an apprentice n spotty yoof was before you get a meter out spend 3x longer LOOKING and listening for an elektrikery fault …and ALWAYS start at the point where the last work was done IF everything worked BEFORE said work.

Back then it was the old style HUGE and noisy click and bash telephone exchange, the Chief engineer had all the meters LOCKED away.

I learned 97%+ of faults we could actually see or hear and after a short while rarely even needed to dig out a drawing let alone a multimeter.

On the bikes I have found this to also work, in fact with most vehicles due to the things like

Earth Return
Bulbs as explained above
Cut outs and other components that give …unusual readings to a multimeter ESPECIALLY in the hands of someone who is not used to vehicle elektrikery can lead you astray real quick.

Which is why many workshops and mechanics take a deep breath at the mere mention of an elektrikery fault …then call in their elektrikery expert, cheaper in the long run than spanding days trying to trace it , changing components and digging around often causing more faults than they clear.

SO if you can’t see it or work it out real quick …then look up your local auto elektrikery guy it WILL save ages in time and money and frustration.

I have worked wiring vehicle electrics and on some occasions after doing the :-

head scratching
replacing the obvious
doing all the basic checks

I have called in my local expert Towza…all sorted in less than an hour and I wondered why I had wasted the previous ** hours Farting about!!!

Thanks for the replies, I will put them all to the test this weekend when I have 5 minutes to poke around!

Don - yes, the connectors are on the left, just to the side of the battery tray.

Mike - I might have left the front side light in (though I thought it should be switched off and out of the circuit?)

Anyway, I can’t diagnose any more from the sofa - going to have to wait till the weekend when I’m not busy with work. Will update with whatever I find to be the problem. Hopefully it warms up a little by the weekend as well!

Ere I just noticed …your avatar …you’ll be that “Millicent Bystander then?”

Ah foiled again Same side indicators front & back tend to be in parallel on the same wires at all times, the only exception I’ve heard of is in the case of these new-fangled injection models that have some computer gizmo wizardry doing it in a completely different way. In which case the lamps seem to be separately switched. Edit ~ I assumed you meant indicator lamp? Well, still the same for front/back ‘park’ lights.

Right, thought I’d update this. Manage to have another fiddle at the weekend. Took the headlight out of the circuit and everything else seemed to work ok so I thought I’d take the headlamp to bits, couldn’t see anything wrong / shorting out so plugged it back in and it’s all working fine again. All I can guess is something must have moved when I took the headlamp to bits and removed the short. Hopefully it stays that way!

Then of course, putting the rear light back on one of the well nuts broke free so it’s currently being glued back in place…

The ONLY glue I have ever found to work is Araldite 2 pack anything else just gives way, used it over the years many times to get me sorted till I could replace a part.

Some time ago I worked at a place that made copper hot water cyls the coils and any thing held with a brass nut had a fibre washer attached that was liberally coated in araldite… messy job and one the new guys got firts IF they lasted that one they got shown other skills, braising copper with gas torch and rods was one I learned and from the big brass bungs down to copper sheet …the copper sheet IS a heck of a skill to learn let me tell you, as one welder commented if YOU can braize copper sheet then you can just about weld anything.

Yep GB, two part epoxy resin is what I used. Hopefully it lasts!