28-10-2021, 08:50 PM
Hello A7 friends.
The Lucas PLC2 switch (Panel, Lighting and Charging) seems to cause more than its fair share of head scratching. I have therefore drawn out its internal equivalent for each of the four settings, plus the wiring for the A7 Ruby. This is as viewed from the FRONT, the rear view would be a mirror image.
The lighting section is in Red. Note that there is an unused terminal marked L which is live only on the sidelight setting, and is switched off when the headlights are on. This is to save current on cars which have sidelights within the headlights, i.e. not the A7 Ruby.
The ganged charging section is in blue. Note the internal links. In the LOW setting the switch is open circuit, so the dynamo field coils are supplied via the "half charge" resistor. This isn't shown, but is usually part of the CFR cutout. In the HIGH, SIDE and HEAD settings the "half charge" resistor is effectively shorted out so as to give full charge.
The separate ignition switch section is in green. Note the internal link from the A terminal. In the Ruby application, the total current through this switch is no more than about 5 Amps. I recommend that no other electrical loads are added to this, or the contacts will suffer.
Details of dismantling and repair have been available on the internet for some time. It's possible with care, but not for the faint hearted !
The Lucas PLC2 switch (Panel, Lighting and Charging) seems to cause more than its fair share of head scratching. I have therefore drawn out its internal equivalent for each of the four settings, plus the wiring for the A7 Ruby. This is as viewed from the FRONT, the rear view would be a mirror image.
The lighting section is in Red. Note that there is an unused terminal marked L which is live only on the sidelight setting, and is switched off when the headlights are on. This is to save current on cars which have sidelights within the headlights, i.e. not the A7 Ruby.
The ganged charging section is in blue. Note the internal links. In the LOW setting the switch is open circuit, so the dynamo field coils are supplied via the "half charge" resistor. This isn't shown, but is usually part of the CFR cutout. In the HIGH, SIDE and HEAD settings the "half charge" resistor is effectively shorted out so as to give full charge.
The separate ignition switch section is in green. Note the internal link from the A terminal. In the Ruby application, the total current through this switch is no more than about 5 Amps. I recommend that no other electrical loads are added to this, or the contacts will suffer.
Details of dismantling and repair have been available on the internet for some time. It's possible with care, but not for the faint hearted !
