Perkins 4108 Wiring diagram

[pappaecho]

A minor irritation, is that the ignition light on the Perkins console has stopped working. Obviously checked the bulb, which is showing a resistance, and when the ignition circuit is on I am getting 1.7 volts rather than 12.
Alternator is charging OK, so no worries there. Perkins manual only covers the alternators and the starter motor, and does not publish a working circuit diagram..
Anybody got one please?

As its a diesel - and a boat one at that (ok - originally a 1950's bus engine / workhorse) .... wiring diagrams for much else is rather dependent on boat.

The ignition light is basically a bulb placed into the 12V exciter feed to the alternator. Usually its a low power grain of wheat bulb or just slightly larger.

You say there is only 1.7V when ignition is on ... that indicates that there is a fault in the supply to the exciter lead. I would switch on ...... put a meter across from +ve supply to bulb (at bulb holder) and to the engine to check 12V is actually available BEFORE the bulb. If not then step back one junction .... with the +ve side. Till you find a 12V reading.

Basically you should have 12v coming up to ignition switch then 12v of to the bulb and excitation of alternator when first position clicked .... ignition switch also supplying 12v to the solenoid when key turned to start.

I take it the engine turns over on the key ? If so then 12v supply to ignition switch is ok. It then indicates a poor connection in the excitation lead / bulb supply.
There is another possibility - my Perkins has a LED bulb in this position ... if it was connected wrong way round - then very little power would flow as exciter .... probably 0.5V or thereabouts ...

The Ignition light - actually is a charge indicator ... works by 12V being supplied to excite the alternator - light is on .... the field coils being excited then alternator starts to generate charge power ... this then develops its own field and the 12v excite lead is then finding an equal and opposite 12v - which effectively stops the light glowing ... effectively 0V ... (Very rough layman terms ....). It's a very simple and effective way to show charge etc.

So - check all connections and wires from Ign. switch through bulb to alternator ... just follow the lead !!

[Roberto]

Paul,

I have a couple of wiring diagrams which might be interesting, PM your email address if you wish and I ll send them, PDF files

r

[pappaecho]

Engine working fine. Up to two weeks ago when you switched on the ignition the bulb lit and went off when the engine started and the alternator cut in. Now everything works but no light - agree must trace back to connectors etc. Boat rewired two years ago with submain and very good earth returns to engine and battery so likely to be ignition switch or positive connector from alternator... will try the meter routew this weekend whilst on the pontoon at Cowes

Is the alternator charging the battery ?

Some alternators only slowly decay on the field coils ... and exciter has very little to do. Some like my alternator decays very quickly and needs that exciting boost !!

If the alternator is charging - then likely failed bulb or connection to it.
If alternator is not charging - then you may have failed field coil in alternator or bad connections..

If you can't find a bad connection - then I would take alternator of and give it to auto-electrics service to test the alternator ...

[pappaecho]

Alernator is definitely charging the battery, as we have an voltmeter which is built in to the solar/wind charger array, and it clearly shows a rise to about 14.2 volts when the engine runs.
As posted before the ignition light used to come on, and now does not, so i dont think it is the alternator circuit causing the problem and is likely to be a high resistance connection somewhere in the circuit

Could be - as it takes very little to excite the alternator to start charging ... it could even be that not enough current is flowing due to resistance to light the bulb. Is the bulb ok ??