Strange thing happen: Engine stops when lights are turned on

[rtollef]

I have a 1972 T250 - a very nice bike - but with a strange thing.

Engine is running smoothly, but when I turn on headlights, the engine stops.

I have changed the recitifier and bought a new battery - but still the error is there.

If I take out the headlight bulb, the engine does NOT stop - but as soon as the head light bulb is in place, the engine is dead.

Any smart suggestions?

Rune, Norway

[jabcb]

Does the bike stop immediately when you turn the lights on?

Check battery voltage:
1) bike off
2) bike on & lights off with bike not running
3) bike on & lights on with bike not running
4) bike off
5) bike running with lights off at low rpm, 2k rpm & 3k rpm

The alternator has a lighting coil to increase alternator output when the lights are on -- there may be a problem in this circuit.

For the headlight installed or removed test, did you have the headlight unit installed & completely removed.
This could point to a wiring problem in the headlight bucket.

[alanr]

you will have to check the wiring.does the motor stop with indicators or brake light turned on.if not check headlight wiring.disconnect headlight wires-start bike-idle-plug in one wire at a time,see what happens.

[rtollef]

Thanks for replies.

The voltage is fine, I even got stabile voltage to the wires that goes to the frontlight... I measured when lightbulb was out.

All lights are in good shape, except from some mystery fault on the headlight wiring. The turnsignal lights, brakelight and rearlight is all in good shape. Even the speedomeeter light.

When lightbulb on frontlight is out, all of the switches can be used, and nothing happens whatsoever. Until the freaking bulb goes in... turning headlight on with the switch, makes engine stop.

Seems like the headlight demands to much power, and that the electrical system for some reason cant provide it.

Question is why? What part or cable must be checked and replaced...?

[markush]

Hi!

Until the freaking bulb goes in... turning headlight on with the switch, makes engine stop.

Does this happen even on higher revs? Have you tested the bulb directly with a batterie? Perhaps the bulb itself has a short circuit?

I noticed that is says 12V / 35 W on the bulb, but I cant imagine that is a problem.

You cannot use a bulb with more then 35 Watt over longer time, with a normally functioning alternator, because there would be not enough power to charge the batterie.
Take a look at these schematics and check the switching of the alternator coils on the light switch.
http://suzuki-gt250.de/elektriknavi/elektrik.php?b=1
Maybe you should also check the individual coils of the alternator on their resistance and ground fault.
http://suzuki-gt250.de/elektriknavi/elektrik.php?b=2

[jabcb]

You didn't mention how quickly the bike stops running when you turn the lights on.

What were the voltages?

[rtollef]

Hello

The engine stops imidiately when turning on headlight switch, or the horn-switch. Non of the other switches gives any problem. Its the same for any RPM. (It happens even when driving, and the RPM is about 5-6000)

I disconnected the frontlight from the regular wiring, put in a new cable which I connected directly to the frontlight, and then tried different voltage sources into it.

1. Connected it to the battery
Light functions very well, but on max light of course, and I would have to mount a seperate switch for this solution. (Not a good solution...)

2. Connected it to the red cable coming from the alternator
Light was weak on low RPM and increased when RPM was going up. At the same time the B-lamp/indicator was on all the time.

3. Connected it to the output from the rectifier (red/green cable)
Then engine stopped as usual when using headlight switch or horn switch.

I just tested the voltage from the alternator, and it gives about 13,5 volts on RPM 2-3000, and increases to about 16-17 volts when RPM goes up to 6000.

What would be the minimum voltage to expect from the alternator, when things are normal?

I found out after that the original light bulb is 35 watts.

[rtollef]

Good golly miss molly

Now it works fine. I got a tip from a guy in USA at Oregon Motorcycle parts and he suggested the following:

Put a new wire in from green / red cable from rectifier, and connect that to the green / white cable that is seen in the switchpanel.

I found the green / white cable in the frontlight house, and put a wire between the two points - and now everything works as a clock.

Lights, horn everything.

Seems like the green / white cable shall give som extra transportation of voltage to the switch and lights, and obviously this connection have been broken or at least bad.

Will put in cables and put the bike together, and celebrate with a ride in the nice weather.

[jabcb]

Your voltage numbers are good.

For T250/T350 alternator specs, see page 17 of: http://www.ozebook.com/compendium/suzi/suzidata1.htm
Page 17 also shows two different ways to connect the alternator.

The stock configuration is:

Recommended change to increase output when lights are off. (see different connection for alternator G wire)


Check to see which way your alternator is wired up.

It probably is going to tricky to find the problem.

A good starting point is to see what happens when you disconnect the alternator.
1) charge up the battery
2) figure out which of the two wiring layouts you have
3) disconnect the rectifier Y/G & R/G wires
4) start the bike with the lights off
5) does it still run when you switch the lights on?
6) what is the battery voltage for steps 4 & 5?

[rtollef]

Problem was solved by wiring a direct cable from recitifier (green/red) and onto green/white cable that appears in the switch and in the lighthuse, front. (I connected them in the frontlighthouse) Probably it has been a problem with the cable in the switch or somewere else.

Now its perfect.

Thanks for all good tips and hints.

Rune

[jabcb]

Good that you found the problem.

The G/W wire connects to the alternator lighting coil.
The lighting switch connects the G/W wire to the R/G wire to provide the alternator lighting output to the rectifier.
(See my pic for the stock configuration.)

You bypassed the lighting switch so that the G/W & R/G wires are always connected.
This gives you full alternator output when the lights are on or off.

So as you noticed, it works good with the lights on.

But you now have too much alternator output when the lights are off.
The voltage likely will get too high if you run the bike with the lights off.
Running the bike with the lights off could shorten the battery life, and burn out the neutral light & stop light.

[rtollef]

You are absolutely right

The green light for neutral is already gone... and I think the horn also stopped working.

So... instead of connecting directly - what could be done as an alternativ?

Probably the problem is in the handlebar switch... but I am not sure about it.

Suggestion?

The wiring diagrams you listed are very easy to understand...

But the part called 'connector' in the diagram - what is that ecactly? (Perhaps a really dumb question... )

[rtollef]

Also:

How to change the neutral lamp indicator? Possible to access it underneath the rpm meter?

[jabcb]

The connector is just the wiring harness connector. It has additional wires for the points & neutral light.

The neutral light is a small bulb that is accessible from the underside of the tach.
The original bulb is probably 3.4W. Commonly available bulbs are 3W & will work fine.

3 reasonable solutions:
-------------------------------
1) modify the light switch so you can not accidentally run with the switched off

2) find the problem & fix the wiring
You bypassed the light switch's control of the alternator output.
Find the problem in this circuit & fix it.

3) replace the rectifier with a rectifier/regulator
Then wire it up like:

[rtollef]

Thank you very much for excellent help.

I will check on different solutions, and see what we end up with. Its mandatory to drive with frontlights on here in Norway, so I might as well always have lights on. Changed the neutral light too, and will use that as an indicator on how it goes.

Perhaps it might be in good balance as long as I always have the pights on.

Thanks
Rune