Welcome to the wonderful world of wire tracing. Hopefully it's the pump, otherwise it might be easier just to run new wires; you could have a rub anywhere from the power distribution box all the way to the pump that might be knocking against the frame in certain conditions causing a dead short and killing your relays.

If you've got an ammeter or DVOM, like it's been said, you can test at the pump or the relay.

Personally, I'd disconnect the pump from the harness and measure amp draw while appling 12V directly to rule it out or verify it's bad - like I said, there's plenty of things that can go wrong between the relay and the pump.

If you do a lot of electrical troubleshooting, you might want to invest in a power probe. http://www.powerprobe.com/powerprobe/PP2.html You can get them for about $70 on ebay and they'd be worth every penny at twice the price.

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.