Hi Peter. Just FYI, I believe you'll find the OP's 780 still had LH 2.2 in 1989. The B230FT didn't get LH 2.4 until 1990, whereas the B230F and then new B234F both got LH 2.4 in 1989 in both the 240 and 700 series. Technically the B234F got it in 1988 as that was the first year of production in Europe only. Also, no 25 amp fuse to worry about in any of the 700s. Near as I can figure, the troublesome 25 amp fuse was placed under the hood in 240s because they ran out of room in the original side fuse panel and were too lazy to design a new panel or relocate one of the other fuses off the panel. The side fuse panel location was already known as a troublesome spot due to possible windshield leaks, especially after glass replacement, so all the more reason to have it somewhere else, except they weren't bright enough to use a weatherproof fuse holder like in the Volvo marine engines.

The early LH 2.4 ECUs sooned developed a bad reputation for the fuel pump control circuitry going bad. That was my first thought for the OP's dead fuel pump as soon as I saw 1989 until I noticed he said turbo, plus those 780s only had turbos. Most of those troublesome ECUs have long since failed and been replaced or a bypass done at the FP relay. I'm glad it's now working for him. If his problem returns then the prime suspect in my mind would be the FP relay or relay tray socket until proven otherwise.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now