Even though I was able to consolidate a lot of fuses and relays in the first Volvo fuse box, there still remained some circuits that I wanted to control with relays. Specifically, the lights (low beams, high beams and driving lights) and, if possible, a relay that would take the accessory items off-line whilst the starter motor was engaged.
I started with the main fuse box from a mid-nineties Volvo 9-series. Volvo had this box near the battery with a set of burly 50A (80A? I forget.) fuses.  From the box, power was distributed to other fuse boxes where the circuits were fused again.  Wow.  Two fuses on a circuit.  That's two more than Citroen used on some circuits.
Here's two views of the box, with the wires and fuses about to be removed, and when I was test-fitting a way to hold the relays in place.  The reason I wanted to use this box is that I could get it nice and watertight.
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here you can see the box, the fuses and the cover.

 
I used interlocking relay holders I found at Waytek Wire. I highly recommend  them. 
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relay holders separated

 
Always, always, always, make a plan.   I sketched the locations of the relay terminals as they would look from at the wire-side of the connectors.
A sharp eye will notice that I have 4 relays sketched, but three blocks.  The three blocks are for the lights, which I wanted to wire up as a group.  The fourth is for the accessory circuit. The three light relays are sketched to the right. 

  1. The heavy blue, red and yellow lines at the top are for power to the bulbs
  2. The line of yellow with red dots are to switch the relays for the high and driving lights
  3. The line of yellow with blue dots is to switch the relay for the low beam
  4. The two blue straight lines from the bottom are to feed power to the relays, one to the low beam, one to the high beam, with a jumper to the driving lights.  Each supply wire has its own fuse in the other relay/fuse box.
  5. The black line is to ground the relay switching circuits.
For each wire that went in, I made a new sketch.  I drew ALL the relay pins, and then one line for the wire that was installed.   Kinda like a CAD drawing in layers, but on paper.  The relay pin diagram is the base diagram, and each wire gets its own layer. I started with the jumper wires, since they were short and I wanted to have enough working room as possible to put them in.  Then the heavier gauge supply wires, then the paired output wires.

The picture gallery below has eight images.  Use the little arrows to either side of the row of small pictures to scroll through all of them.  Click the image to see a larger version.

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The brown switching wire for the high beam, with a brown jumper to the driving lights

 
After I set up the power and switching circuits, I made the ground wires.  Relays don't pull very much power at all.  So, using smaller gauge wires is ok.

 There are six images in this set, click on the little arrow  at the right to see the last image.
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Four wires, two long, two short, so they would all end at the center of the block

 
pack the underside of the relay connections with dielectric grease

Feed the wires through the hole.  One at a time is easiest.

The box with the wires pulled though, and the blocks settled in place.  I have to figure out a way to anchor them in place.

The wires from the hole at the bottom of the box.  I need to create some type of grommet at the base to make it watertight.