Had fun with the multimeter tonight! I have a rear light that works with side lights but not with a brake light. Firstly, the obvious things - the horn works so I know it's not the fuse. And if I short the side light over to the brake light connector within the light unit, the brake filaments come on, so it's not the bulbs or the light unit itself. I have checked the rear brake switch and that seems to be working OK. I've checked the front switch but got inconclusive results, probably because I found it difficult to get a good contact with the multimeter probes. I have continuity on the grey/red wire between the rear switch and the contact in the light unit. I have continuity on the purple wire from the rear switch to two pins in the connector next to the rear suspension damper top mount - though from the wiring diagrams this purple wire only seems to go to the front of the bike, so not sure what is happening there. Not sure what else to check now?
Jammy, your description needs clarification. Is your rear light/number plate light working ok and the brake light is not working (when the brakes are applied)? Or is the brake light not working only when the rear light/number plate lights are on? For starters from me, do the rear indicators work ok?
The side lights within the rear light unit work fine. I'm not sure about the number plate light (which might be an aftermarket tail tidy), I'll double check tomorrow. All the indicators definitely work ok.
Jammy is this a new fault? You indicate a tail tidy is fitted can you see how the circuits are installed through that? Everything at the back shares a fixed earth path through the ecu power connector (the big three pin one under the RHS of the seat). When you have a look tomorrow you may want to try continuity checks between pin B of that connector and your light assembly. Also can you see and trace the rear light loom where it passes under the seat unit?
The bulb, if it's a conventional tungsten bulb is a double filament stop/ tail bulb. The brake light filament is brighter and probably more prone to failure. The tail light filament can easily be intact while the brake filament has broken. Other thing is that the bulb has offset pins that only fit one way. If you insert it the wrong way round both filaments won't light properly even if they're intact.
Ducati brake switches seem to be famed for being poor quality but it's a long shot they both fail at the same time. I would buy a new bulb for the price of it and then make sure the holder is very clean and all the connections. Irrespective of the horn working I would change the fuse as well
Double check the switches to take them out of the equation. Disconnect each one and short the connector out on the loom side. That'll prove the wiring or not.
It's not a new fault (well it is) - the bike has been stood for a while. The brake lights were working previously, they aren't any more. I guess that suggests a corroded wire or connector since nothing else has changed! It's definitely not the bulbs. With 12V to the brake light filament connector the brake lights come on (even with the side lights on). I've taken the connector apart at the rear brake switch and tested for continuity with the brake lever at rest and pressed down and it seems to be working fine.
When I bought my 999, the front brake switch didn't appear to be working. Derek suggested the connector, so I disconnected and reconnected several times and it's been perfect ever since. Do you have continuity between connector/s and bulb holder/earth?
Would problems with the front switch interfere with the whole brake light setup? I believe I have continuity on the earth and the bulb holder, but I'll double check later. I seem to have continuity on all the other connectors for the rear brake switch and light. I think I'll take the earth off and clean it up just to rule this out and as some good preventative maintenance. Is it the one by the ECU? I think the one for the switch is in front of the rear damper.
Jammy, the easiest way to prove the earth is to switch it all on then take a separate flying lead directly from the battery negative post to the rear light assembly to parallel the loom earth path. If the fault disappears you have a loom/connection problem on the earth side. The way the two switches are wired means a failure of one of the switches should not affect the other. They both share the same supply circuit but break into that circuit in different locations on the loom and share the same 12v line to the light assembly. As a matter of course you need to separate and check the cleanliness of the 10 way plug under the front rhs of the seat, the three way ecu power connector and the 22 pin round connector under the front RHS of the tank.
Op says if he crosses side light feed into brake light feed both filaments are lit .....this tells me earth path at bulb case is present .....op when you do this does brake light filament light at full strength ? if yes move on to this , if it's dim , supply the bulb case with seperate earth like Denzil says there . The two wires at brake light switch is there battery volts on one of them ? use your meter but I prefer to use a bulb type test light ....not led type ....led types just confuses the issue as led will light of hardly any current where as bulb test light draws out some current . If there is no battery volts on one of them wires that needs to be traced back to its source ...I'm assuming it must be a common supply to both front and rear switches .....I'm also assuming that the brake switches are carrying the live supply to the bulb and it's not some mad switched earth but I dought it
What Nellie suggested makes total sense to me. If you stick a multimeter probe in each side of the connector for each switch and then get continuity when you operate the lever, you can eliminate the switch as being the problem
Lee, the switches switch live so they do have +12v on one side, the earth for all the rear lights (inc indicators) is permanent through the ecu power connector. All I would do is short the switch at the loom connector to energize the circuit then probe for 12v along the circuit path. The supply comes from the fuse box and supports the horn and brake lights
Yes Denzil short switch and back probe to source good way of going at it like you say ,perhaps where it branches off from fuse is where it's lost seeing its lost front and rear switching
I've shorted the rear switch, lights came on. So even though there is continuity it seems the rear switch is at fault. Is there any way to test the switch in isolation? Does it ground through the switch body or through the wiring? Then moved on to the front switch, the two bullet connectors had corroded, as had the mounting bolts/nuts. Eventually got the switch off and again, shorting the wires made the brake light come on. So it seems both switches have independently failed over the last year whilst it's been laid up! Having said that, the bullet connectors for the front switch were in a bad way, so I may see if a new (weatherproof) connector resolves the issues with the front switch.
Rear switches are notoriously unreliable. I'd fit a new one... once they've gone they rarely repair. I'd fit new bullets to the front switch. It's just bad luck rather than a huge design flaw. If you change the connections, should you have to fit a new switch in the future then you'd have to mod that to fit the loom connection you've fitted...
