Rear light problems

[EddieH]

Hi, I need some help! I have a used square'ish MZ rear light that I'm trying to fit to my TS150. The old battered light that came with the bike is round with 2 bulbs (stop & tail). This square one is a twin filament (one bulb, stop & tail) with two earth spades on the backing plate (I'm calling the supply to the back brake an earth). So each filament has a power supply spade and an earth spade.
The two supplies are one from the coil (black)and one from the ignition switch (grey). The black one earths through the brake switch and works perfectly when the grey one and its earth is disconnected. When I then connect the earth for the grey one the brake light goes on. When I disconnect everything and connect the grey one and it's earth then I get the other filament coming on when the ignition switch is in the side light or dipped beam position.
Can someone who recognises my description of a square'ish twin filament bulb rear light tell me what MZ it belongs to and how earthing the two separate filaments can be done? I am resigning myself to buying a new light but I would seriously like to know how this light works and why there are two earth spades on a common backing plate.

[DAVID THOMPSON]

use ohm meter to see if the 2 grounds are common to each other if they are the 2 other wires

go to a dim and a brighter lamp the dim is run the bright one is stop

and the source is the fuse that runs the instrument lamps so if the fuse is blown you know

by the missing on lamps THAT MEANS NO BRAKE OR TAIL LAMP

if there separate hook the grounds together and do above

i can do a wiring drawing if you need that

DAVE

[EddieH]

So yes I can confirm that the grounds are common and that both filaments are powered (dim & bright) but there are no fuses on the bike apart from the main 16 amp fuses on the battery. So my problem remains that the stop supply is ground out by the run earth leaving the run light on continuously when the ignition is on.

[EddieH]

Sorry I meant that the stop is on continuously grounding out through the run earth

[Puffs]

On advising you on what bike that square'ish tail light belongs to: best post a pic. Or compare it yourself to what several vendors offer for the various bikes. I believe the original for the TS is round, and to me there is an appeal in keeping such old bikes close to original.

On which wires to use: you have to decide that on the basis of what the multimeter tells you; wire colours are not necessarily reliable.

[Blurredman]

I have successfully done similar with a 251- in that I covnerted to round, seperate globes- because that was all I had on hand at the time. I have since got a square one with a bilux bulb.


I see one thing that might be an issue (?), the rear brake on MZ's until the 251 use the integrated drum stop lamp contact. There isn't a switch as such- but the earth is connected (I believe it is earth) and that opens the circuit to the bulb. The earth being essentially the connection from the drum and spindle all the way up to common earth. The 251 uses the more common (now) plunger type of switch which is actuated by a spring connected to it from the pedal itself.

Could this be an issue?

[dave47]

Surely rear lights with a single "stop and tail" bulb can only be switched from the live side, as the filaments share a common earth. Unfortunately as Blurredman says, brake switches on the older MZs such as the TS150 can only switch on the earth side, and therefore require separately earthed brake light and tail lights. Even 2 bulb units won't work if the bulbs plug into the same metal plate. I don't think there is any simple way around this, other than to design your own brake switch!

[jam23a30]

I think the previous post are on track, your square light needs 2 live feeds and has a common earth, if you really like the square light you could take a feed from the fuse box and wire it through a "old british bike" type of brake switch operated by the brake rod to power the stop light filament. The switches aren't expensive but won't look original. Pay your money and take your pick as you prefer!

Andy