starts,put on lights and all dies

[jacquesvins]

Hi,
Just got my 125 MZ d reg going after really struggling to get spark for months..... ran well so engine, carb etc ok but as soon as I put lights on all went dead. Replaced blown fuse but still no spark - again.... what now....any ideas....thanks, Jacques.

[DAVID THOMPSON]

what year is a d reg as i am in the USA and we do things by the year
if its a 2 smoker look for shorts and bad grounds (earth) connections

and do check the battery
dave

[jacquesvins]

Hi Dave, a D registration represents a 1985 model in the UK.

Thanks for your comments - it has been a really massive job to get the bike going - all electrical problems. Deciding factor that ensured the first start yesterday was a new ie seperate and additional earth wire to the negative side of the battery, but as I said running fine and then tried to switch on lights and all died. Had used the main switch situated on the top of the headlight to put the lights on.....
Strange thing happened when i turned the switch back to the start position and tried to kick the motor over again, there was no more spark.... all was dead.....battery checked and still fully charged - also blew a 25 amp fuse, but when new fuse added, it still would not spark.... quite sick of kicking the motor over.....will do what you suggest....thanks again,

Cheers Jacques.

[DAVID THOMPSON]

being its an 85 model a good clean and rebuild of the switch
may be in order
and a close look at all the wires

all my mz bikes are 1995 or newer but electrical has been the big issue with each of them

dave

[arry_b]

Check all of the fuses. There should be a fuse on both the live and the earth.

[DAVID THOMPSON]

never seen fuses till now in the ground wire except on 2-way radios
so thats a new one on me

and the switch on the heater blower motor on my nissan truck is in the ground lead
really gets you head scratching when you run into it the first time

and check the ohm meter often nothing like a fowl up caused by bad test gear

dave

[arry_b]

There are a couple of posts showing nice wiring maps:

http://www.mzriders.com/viewtopic.php?f=20&t=4986

You can see the dual fuses on there.

To the OP - when does the fuse blow?

Parking lights / ignition off?
Sidelights / ignition on?
Low beam / ignition on?
High beam / Ignition on?

More info please.

[jacquesvins]

Thanks for the tips so far....
When the bike is running, ie idling correctly, as soon as the headlight switch is turned to the left, ie to put lights on the bike cuts out immediately. Also then there is no spark to restart.... really weird.

Looks like the switch needs to be the start of my investigation.....

Cheers Jacques

[DAVID THOMPSON]

i am thinking short in switch
or the wire it connects to when switched

TRY IT WITH THE FRONT BULBS REMOVED IF IT BLOWS LOOK AT THE TAIL LAMP AND SOCKET
and the wire going to the rear
I HAVE HAD SEVERAL REAR SOCKETS FAIL OVER THE YEARS ON SEVERAL BRANDS OF BIKE

and poor quality fuses
i raid old cars that my stepson is taking to the crusher for fuses and bulbs made in the 70's
they are cheap and seem to last longer

hope its not one of those wonderful bikes where 5 or 6 people worked on it that though they
knew what they were doing

[arry_b]

Leave the main switch alone for the moment.

A few more questions:

When the engine isn't running, what happens when you put the lights on? They should work - one click past "on" = sidelight and tail light, two clicks headlight and taillight.

With the bike running, lights off, does the brake light work when you operate the front and rear brake?

Does the rear light unit have one or two bulbs in it?

The bike is ticking over, all lights off. You move the switch *one* click to the left and the bike cuts out. Correct?

What do you need to do to get the spark back once this has happened?