Customising bike, issue with new tail light...

[awf1974]

Hi there guys,

I am customising and modifying my GZ and have recently purchased a Sparto tail light copy but am having some trouble installing it.

The light came with two wires, red and black, I thought no worries so I dismantled and clipped off the old tail light and housing to find three wires, one brown two black and white.

On the original light the brown and one of the black and white are attached to the rear of the bulb/globe, the other black and white is earthed into the housing.

So I strip the wires back and temporarily attach them to find out what does what, I can get the 'minor' (tail light) filament to come on without a worry just by attaching brown to red and solid black to one of the black and whites, but I can't get the 'major' (brake light) filament to come on no matter what I seem to do - I am operating the front lever and/or footbrake by the way...

I am able to make the brake light filament come on permanently (without operating brakes) if I attach red to brown, solid black to black and white and the other black and white is earthed to the housing.

So I go back to the original light to see if I can figure out how that one worked, brown to brown, black and whites together and the tail light comes on but not the brake light...

So my question is, do I have an issue with my wiring or is the issue elsewhere? It's doing my head in! The brake light filament on the original light is intact.

Thanks, Andy

[alantf]

Even though there are two black/white, one is power, & the other is ground.(or they're both power, & the brown is ground) Make sure that you haven't mixed them up, as they won't work properly if you've got them wrong.

Next thing to do is :- switch on the ignition, then with your meter set to voltage, test between each cable in turn (on the bike wiring harness) to ground. The cable that shows a voltage is the tail light +ve. Then hold the brake lever closed (with velcro, a rubber band etc) and test between the two remaining cables & ground (in turn) The one that shows a voltage is the brake light +ve. Set your meter to ohms & test between the remaining cable & ground. You should get zero ohms (or near as dammit).

Next step is to connect the cable you found as ground to the ground connection of the new fitting. With the ignition switched on, touch the cable that you identified as tail light to either red or black. If the correct bulb lights up, fine. If not, then touch it to the other cable (red or black) This should light up the other bulb. Once you've done that, the other cable must be the brake light, so touch the remaining two wires, & the brake light should come on when you squeeze the lever.

[awf1974]

Good on ya Al,

I'll borrow a multimeter and give it a crack in daylight tomorrow...

[awf1974]

Hi,

Ok, I bought a multimeter because I reckoned it was daft not to.

Anyway, here's what I found...

Ignition on, meter set at DC voltage, black meter probe on mounting bolt, red meter probe on brown wire, meter showed 6V, later on 3V as I think the battery's starting to die with all my mucking about. Engaged brake lever with zip ties, tested other black and white wires, both showed -ve 0.1 mV (or thereabouts).

Turned meter to resistance, all three wires showed 0?.

Does this mean I have an issue with the brake light switch/wiring?

Ta, Andy

[alantf]

First thing, charge the battery, then test across it to prove that you've got 12v or above. Don't worry about the -ve showing on volts scale, it just means that you've got the two probes the wrong way round (no biggie). Repeat the voltage tests (with the ignition on), then let us know the results. BTW, if you still don't get a voltage reading between one of the other two wires & ground, then yes, there is a problem with the brake light circuit. Did it work before? I'm not sure if there's a fuse in that circuit, so it may pay you to check the fuses while you're waiting for the battery to charge.

[awf1974]

It has worked in the past but I can't recall the last time I checked the brake light, there's one fuse for the whole tail light assembly not individually for tail/brake light.

[alantf]

According to the owners' manual there's one fuse for the brake light, indicators, neutral light, indicator warning light, & horn, and another fuse for the tail light, & speedo light. So that's separate fuses for the tail light & brake light.

[awf1974]

Gotcha, just found that in the manual myself, the fuses are just labelled 'tail' and 'signal' in the actual box. Indicators are working as well as neutral light and horn, so fuse is ok.

Charged battery for 24 hours, have now got 12V to brown wire, but only milliVolts to other black/white wires.

Used continuity on multimeter to track one of the black and whites back to the little black plug that connects to the spades that jut out underneath of brake housing, the switch assembly ref #6 p.40 of parts manual. Continuity exists between black plug and far end of wire, do I need to track this wire back to battery etc or is the issue likely to be in this assembly?

Andy

[alantf]

First of all, test (voltage) to ground at the input side of the plug. If there's no voltage there, then you need to do this at every connector, back to the battery, until you find the break. Just had another thought - while you're doing this, physically check the cables as you move along. It's been known for cables to rub through, and break, due to vibration & rubbing.

BTW, what do you mean by "the plug that connects to the spades that jut out underneath the brake housing"? Can you clarify this? As far as I'm aware there's nothing near the rear or front brakes. The front brake switch is in the brake lever, & the rear brake switch is half way along, under the bike. All that happens is that when you squeeze the brake lever, the button switch closes the circuit, and when you press the pedal, the pull of the brake cable operates the (adjustable) switch under the bike. :??:

[awf1974]

Attached is page 40 of parts manual, part 6 is "the spades that jut out underneath the brake housing," there is a plug on the wiring harness that attaches to these one wire of which runs all the way to the tail lights.

[attachment=0:2t58z5fz]p.40.pdf[/attachment:2t58z5fz]