ES250/2 Disappearing Voltage

[Michael Jennings]

Hello, I’m having an intermittent problem with my 1971 ES250/2 electrics. Sometimes, when I turn the bike on there’s nothing working in the electrics. The battery is good and registers 6 plus volts and when the ignition is off, there is a potential between the battery, feed fuse and feed wire to the ignition switch and earth. When I turn the switch on, the voltage disappears at all points except between the battery terminals. I’ve replaced the ignition switch and cleaned connectors etc. but am a bit stumped now. It seems as if, when the ignition switch is turned on, the battery earth somehow disconnects. Any ideas gratefully received!

Mike Jennings

[Brian Cairns]

Sounds like an earthing issue? Need to check all connections and earthing points?

[Brian]

I would suggest using something like a 21W lamp with flying leads to check the wiring. You need something that will draw some power (voltage plus current, not voltage alone) from the system. Modern multimeters draw a minute amount and are not particularly useful for finding bad connections. They’re perfect for finding broken connections though. To use a water analogy the water pressure (voltage) in your home is essentially the same as the pressure in the Main outside but flows (current) less because of the restriction of the smaller bore piping, equivalent to a bad connection in vehicle wiring.
Faultfinding really is just checking in a methodical way, start at the battery and work away connection by connection. Don’t try to check both positive and negative at the same time i.e when checking the positive line leave one of the wires connected to the negative terminal whist you check the connections on the positive side and vice versa. A bad connection will cause the lamp to be less bright. And of course if the lamp doesn’t light up well when put across the battery then you’ve got a really simple solution, recharge or replace.

[Michael Jennings]

Hello Brians,

many thanks for your replies and the useful info. Many years ago I had to push a TS150 14 miles home as the regulator had packed up so I decided to have a fiddle with that after rechecking the battery earth – Bingo, everything worked after I’d gently moved the mobile switching points, so I’ll be fitting an electronic regulator, which I bought for a TS125. Do you know if there is any reason not to fit it to the ES250/2 as they are both 6v?

Cheers, MikeJ

[Brian Cairns]

I fitted an electronic regulator on my 150 TS, 6v , no issues.

Good luck

Brian

[Michael Jennings]

Hello Brian,

thanks for the confirmation,

Cheers, Mike

[Matthew Nichols]

But that doesn’t necessarily have any connection to your ignition issues?

[Michael Jennings]

Hello Matthew,

thanks for the reply – I’m thinking that somehow the ignition switch was earthing via the regulator if the regulator switching arm was stuck closed but that’s just a surmise. It seemed to instantly solve the problem when I moved the switching arm by hand. My old 150 had a similar problem caused by the mechanical regulator.

Cheers, Mike

[Michael Jennings]

Hello again,
I was checking the ES250/2 again earlier this year and found that the problem was corrosion in the ignition switch. The switch has little steel pins which extend through the base of the switch between the brass switch rotor section and the base terminals and the pins had corroded causing intermittent resistance. The switch was a new one but the pins don’t seem to have been plated so the steel started to corrode almost immediately, and the contact surfaces at the ends of the pins are very small. I made stainless steel replacements and fitted them with no problems since. You need to separate the upper and lower halves of the switch and the pins are visible when you remove the rotor.

Cheers, MikeJ

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