Ive fitted air horns to my 740 and mine is negative switched, I think this is the way Volvo do it. Also I didnt use the standard size cable because it is way to thin and resulted in the horns not sounding very loud, I replaced it with some 8 gauge straight to the battery, much better.
You can check if it is negative or positive switched with a multimeter using the existing horn wires but im sure it will be negative the same as the 700's.
Cheers,
Richard
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