This business of “load shedding” when starting was worrying me, because I wanted to install a push-button starter and not screw things up in the process.

So I did some homework.

I checked the function of the ignition switch properly, and it looks like this (on the left):



This shows that the switch can indeed provide for “load shedding” when starting, but then red should be connected to switch terminal 75 (not 15) and there should be a dedicated connection from switch terminal 15 to the ignition coil. This configuration would then also disconnect power from the coil (but not the other electricals) when the key is in position I (Garage), which made sense.

So, where was the dedicated wire for making the connection between the switch and the coil? After spending a long time looking for it, which included unscrewing the dashboard, I am now sure that there is no such wire. There is only the brown wire with connector coming out of the wiring harness at a point next to the fuse box and which, as far as I know, has always been connected to terminal 2 of the fuse box (un-fused side). It goes to the coil. This must be the intended route for connecting power to the coil. This is also the way it is indicated in the wiring diagram in my handbook (included in my original post).

But the wiring diagram does have some mysterious dotted lines and an unidentified indicator lamp on it, which have always puzzled me. In my search for a better diagram I found the whole series for the Amazon on the Networks Volvoniacs site:

http://www.networksvolvoniacs.org/mediawiki/index.php/Schaltpl%C3%A4ne

And this cleared up the mystery!

The last diagram in the series (the one for the 123 GT) includes the circuitry for the overdrive and rev counter, drawn in dotted lines. It has obviously served as the basis for the one in my handbook. My car was one of the latest (assembled in 1970) and was said to include features of the GT, but did not come with an overdrive or rev counter. It turns out that the mysterious dotted lines are leftovers of the overdrive and rev counter circuitry. They should have been deleted altogether, but the job seems to have been done in a hurry. The stray warning lamp turns out to be the overdrive indicator light which they forgot to delete.

So, I am now convinced that red should be connected to switch terminal 15 (and not 75), and that, when Volvo did away with the armoured cable, the ignition coil was wired to get its power (switched but un-fused) from terminal 2 of the fuse box. With this configuration it is no longer possible for power to be connected to the auxiliaries but not to the coil, nor for “load shedding” to take place when starting. The “load shedding” feature of the ignition switch was therefore not used. Instead, terminal 75 was used for the cigarette lighter.

This made it very easy to add a push-button starter, which I have now done. Simply connected a push-button switch between terminals 15 and 50. No OR-ing diodes required.

Simplesimon