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Assuming the new alternator is fine, then if the battery is too flat, then the alternator may not charge even though you have jumped it. One way is to use the donor vehicle to run its engine to charge the dead battery for 10 to 15 minutes. Then start the engine and disconnect the jump leads - if the "flat" battery now has sufficient power it should continue ...


There is an excitor cable on the back of the alternator which tells it when it ought to be charging. If this is faulty, the alternator will not start to charge the battery, even if it's a completely working unit. If changing the alternator didn't work, the likelyhood is that there is a fault somewhere in the wiring loom for this (possibly even a fuse).

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