I spent a lovely weekend rewiring the wife's Volvo V40

This 2002 V40 model has a Central Electronic Module that contains various relays and stuff like that to control the lighting, wipers, etc. Needless to say, some of the stuff inside has failed. First of all one dipped beam headlight relay failed (or maybe both) and so I got another CEM box from eBay. This worked except it was for an S40 (saloon) rather than the estate V40 (my mistake to assume they were the same) and the rear wiper didn't work (S40 doesn't have one).

So I wired in two external relays which fitted nicely in a relay holder close to the CEM under the dash. I had HID's fitted and these were fine for quite a while and then one of them packed up. It seems the ballast unit failed, but it seemed to cause other problems too. After getting through plenty of 15A fuses I found out over the weekend that there is a short in the headlight unit itself. And in the process some more stuff in the CEM has given up the ghost (I heard it fry inside) like the lights - all of them. So no sidelights, side marker lights, tail lights, headlights, main beam, fog lights, instrument lighting, nothing. And the other S40 CEM box doesn't work either. Bu99er.

So now I have almost completely bodged all the wiring for the lighting, bypassing the lighting switch (apart from the fog light switches) and wiring L and R headlights in parallel from one relay (both with new slimline ballast HID's). I have the side and tail lights, headlights and instrument lights working OK, running off an ignition switched supply and bypassing the lighting switch and CEM, but at the moment no main beam or fog lights.

So after that long rambling introduction, here's my question: do I need a "latch relay" to make the main beam and fog lights work? The main beam switch stalk supplies an earth signal when pulled in position 1 (to flash the main beam) or in position 2 it's supposed to toggle on and off by supplying a brief earth signal to what I think I need is a "latch relay". Plus I think I'll need a normal relay to the "flashing" bit?
The fog light switches also supply a momentary earth each time they are pressed, again they don't lock in position.

As I understand it, the latching relay switches between one circuit and another upon receiving a momentary signal (earth in this case).

Each latch relay is £20 by the look of it, so I'd need 3 of them plus a normal relay.

If the wipers give up too (and whatever else is controled by the CEM), I might have to chuck in the towel and get rid of the car...