I own a 87-740 non turbo that has around 250,000 miles now.
In july of 2000 at 134,640 miles, after hearing about this wiring fiasco I did an inspection of the wiring harness, and discovered the wires were having problems in a few areas. But mostly where the wiring was exposed.

I pulled the wiring harness out away from the engine, stretched it out and repaired every place the I found damaged. I then rerouted the harness away from the engine and around on the drivers side of the engine compartment. It was necessary to do some extensions of some wires so they could reach there destination(fuel injection, temp sensor,etc .

Since then,upon inspection Ive found a few other areas that needed repair, but again always where the wire is exposed. The one that I liked least was the when the wire to the starter solenoid shorted(more exposed wires). It went bad right at the connector. I just cut it and ran a new wire. Starts like new now. I will admit that it had me going for awhile.
The last one being when passenger side license plate light went out and I discovered that it was on the same circuit as the parking lights. The drivers side parking light wiring was exposed at the front of the car and caused the fuse to blow.

Ive examined wires inside the harness and the ones ive seen look in excellent condition. I also inspect the wiring on a regular basis.

If you were to go this route it would probably depend on the conditon of your wiring. Ive seen pictures of some 740 wiring where clearly replacment was the only option. You would also want to make sure you know how to make good splices(I soldered and tapped and shrunk wrapped)and dont scrimp on materials.
Theres also liguid tape and double sided electrical tape that is excellent.

It would also help to own the volvo green electrical diagram book(or equal, or better). It is a godsend. It has a chart(and pictures) showing all the wires, where the connectors are, what color the wires are, and where they go. Priceless.

There you go. Good luck.

Larue.
I forgot to mention: The car is high and dry in california(sacramento) and always has been. This may make a big difference. But I dont know.