but I did find where my cars problem was. I removed the pump from the trunk and took the cover with the four screws off the back. Inside there is a circuit board with wires attached. I lifted this board away from the chamber that it was mounted in. Underneath I found that the board was connected to two long, small width spade connectors. I cleaned these connectors and bent them slightly for better contact. Also on the board is a small relay. I cleaned all the contacts on this. I then put it all back together. It all works perfectly now.

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1983 300SD
200000miles