Regarding the '87 740 Turbo with the power drain, if you haven't read Dave Bartons website yet on replacement wiring harnesses, it's worth your time:
http://www.linkline.com/personal/dbarton/WireHarnesses.html#UsedHarnesses

As for a decision between a dirt cheap 740 (with some DIY work) and the 780, that's a tough call, but I'd lean towards the 780 and try and work the price down. I own a pair of 780s and REALLY enjoy them. One is an '88 with the V-6, and the other is an '89 with a Turbo-4 which I purchased after it was hit from the rear end, and I'm attempting to restore it. The Turbo versions of the 780 were available from '89 through '91 and have the B230FT (same engine as found in the '87 740), but they also have the Turbo+ kit as standard equipment from the factory. The '91 780s come with the later Turbo++, but it was the last year for the 780 and only 500 cars were made and all of them were shipped to the USA (all 500 were turbos since the B280 V6 had been discontinued at the end of 1990). The Turbo+ and Turbo++ systems are basically a boost controller that allows a few extra psi of boost after the engine has reached a specified RPM (typically 2,500 or 3,000). Any 740 Turbo or 760 Turbo could be equipped with Turbo+/++ as a dealer accessory, and they are identified by a small black computer bolted to the front of the air filter housing. However, just like the 780, a Turbo+ add-on kit is somewhat rare and most people who are looking to upgrade their red-block Turbos typically opt for a salvage-yard-special Saab APC boost controller rather than pay the expensive prices for the Turbo+.

Regarding the V6 versions of the 780, the B280F engine is the cream of the crop as far as the PRV-6 engine design. The earlier predacessors B27 and B28 were used in the 260 series cars, and the early 760s. These 1st and 2nd generation PRV-6 engines had small oil passegeways to the camshafts that could easily become clogged if oil changes were missed, -and thus cause the unusually soft cams would wear down and cause the engine to self-destruct. At the start of the 1987 production year, the B280 replaced the B28 and the previous problems were fixed (most noticably a set of harder cams and vastly improved oiling). When comparing the B280F (PRV-6) to the B230FT (Turbo-4), the B230FT offers a bit better horsepower, but the Garrett T-3 turbo takes a bit to spool up. The B280F offers a bit better low end torque when accelerating from a stop. For obvious reasons, the B230 block is easier to work on and fewer problems are usually found. The B280 block is water jacketed engine, is a bit wider, all the spark plugs are easily accessed from the top, and there's no turbocharger to maintain. Also, the B280 valves can be adjusted using a wrench, a screwdriver, and a feeler gauge (should be done every 30k to 50k or so). The B230 requires a set of special shim-pucks to set the valves to proper tolerances, but requires less frequent checks/adjustment. Should the unthinkable happen (engine run without oil, or cooling system failure, etc), the B230 block is easy to rebuild and parts are affordable & available. On the other hand, the B280 block is not as easy to rebuild, requires special spacers and seals for the pistion liners, and few mechanics have the experience to do so. However, should the B280 block fail, a conversion to a B230F or B230FT is easily accomplised and has been performed by numerous people.

As mentioned before, all the sheet metal on the 780 is custom for only that car. With only 4,000 to 5,000 vehicles imported to the US, they are somewhat scarse (but I do know of a few scattered around in salvage yards across the country). Headlights, tail lamp assemblies, corner markers, grill, airdam, etc, are all custom to the 780. The car chassis and suspension is exactly the same as a 760 GLE for their respective model years (imported to the US from '87 to '91). They only come in automatics, and the interior is hand stitched Italian leather. The interior dash and door trim panels are real birtch wood (not fake plastic), and the sound system is second to none for it's era. If you want to add a CD changer to the factory radio system without any major work, you can swap out the radio head unit (keeping the EQ and amps the same) with a later Volvo CR-814 that they started using in the '91 and up Volvos. The CR-814 is compatible with Alpine's M-Bus system and thus allows for you to add a CD changer in the trunk. (FYI, much of Volvo's audio equipment came from Alpine and bears the respective tags.)

While the 780 is a very unique car (and the last 2-door coupe of the RWD Volvos), many of the design features that the Itialians used were copied by Volvo in their 960 series. Comparing a 780 to a 960 side by side, you will find many similarities, expecially in interior layout and door height design (both of which have low cut door sills and provide a great arm rest while driving and lots of visibility).

By the time you get through reading the following website, you'll probably be thinking really hard about trying to talk the dealer down on the 780. -and besides, a car that cost $40K 15 years ago typically has lead a sheltered & pampered life.
http://www.geocities.com/MotorCity/Garage/6570/

When negotiating a price with the dealer for your 780, look closely at the air dam assembly and the rear side windows (at the base). The air dam on these cars is VERY expensive and is easily damaged by parking barriers. My '88 is missing about 25% of it's air dam, and the '89 is missing the whole thing. The rear side glass is probably the only significant rust spot on the car to worry about, but when it rusts, it rusts badly. There are some concealed drains and tubing to remove the water from the base of the window glass, and if these become clogged it can turn disasterous very quickly. If any evidence of rust is showing at the window base, ask the dealer if you can pull the interior rear panel for futher inspection. What you will find will either convice you to look elsewhere or give you a big bargaining chip in price negotiation.

Lastly, take a look at some previous post on the 780.
http://www.brickboard.com/RWD/index.htm?id=660433&show_all=1
http://www.brickboard.com/RWD/index.htm?id=708188&show_all=1
http://www.brickboard.com/RWD/index.htm?id=703458&show_all=1
http://www.brickboard.com/RWD/index.htm?id=687976&show_all=1
http://www.brickboard.com/RWD/index.htm?id=707227&show_all=1
780 Window rust part 1
780 Window rust part 2, and instructions to pull interior trim panel

God bless,
Fitz Fitzgerald.
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'87 Blue 245, NA 230K
'88 Black 780, PRV-6, 144K
'89 Black 780, Turbo-4, 94K