I'm trying to determine if an 88 740 non turbo engine wiring harness part number 1398765-4 will fit on an 87 740 non turbo, or what model years it can interchange with. Any ideas?

 

if both cars are LH2.2 (Bosch injection), it should fit, at least VADIS (the volvo parts number system) thinks the 88 LH2.2 cars used that same part number harness as the 87's. 88-89 they introduced Regina as an alternate injection, these would be completely different harnesses.