serk I bought a standalone LS1 harness from 12Volt Customs then interfaced with the Volvo engine connector that's on the firewall above the stock Volvo engine intake manifold. I've got an early 240 though, so it might be different with the later ones.
serk All the harness needed was Key On, Crank and it took care of everything else. The same engine connector runs the stock dash cluster as well, and Dave Barton has a good page for the wiring of it: https://www.240turbo.com/240gaugewiring.html
VolvoHordz I have done a previous extension search for the same thing. Best I could find -ozvolvo.org/archive for a full 1993 wiring diagram which is very similar. Also has a system by system diagram for a 1989 which should be exactly the same as an 1988.
