There is a very useful gadget available that I find useful for this type of problem. It is a small digital ammeter with an adapter on the end to fit directly into blade fuse holders. I have seen them on ebay for £12.99 and even cheaper on CPC Components at £8.18 +vat (stock no INO4874), there is also one available on ebay for mini blade fuses as well.
I have had a couple of fuel pump issues with P38 Range Rovers recently and found that fuel pumps on the way out draw about 8 amps but new ones draw about 3.5 amps.
Obviously if the problem you have is an intermittent short in the pump unit then a meter is not much use.
HTH Shaun.
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