I'm trying to make sense of a fuel pump issue that come up while replacing the gas tank of an 89 240.

The car was running just fine, but had a rusted, leaky tank that needed replaced. Everything was going well, until I tried to take a short cut and put the sending unit in the tank while I was in my pit, rather than try to fish it down through the hole in the hatch. The sending unit was in place, and my buddy was supposed to be supporting the tank while I started bolting it back to the frame, but he lost his grip and dropped the tank. We were working in a six foot garage pit, so when it fell, it ripped the harnessing from the sending unit. Awesome. Luckily, I had a spare sending unit, but since the harnessing was all messed up now, I had to splice all the wiring back together. After we got everything patched up and got the tank back in, the car wouldn't start. I thought for sure there was something not wired correctly, so I went back through the wiring several times, and verified that the pre-pump was indeed kicking on. Still, no start... After doing some more investigating, I found out that the main fuel pump wasn't kicking on. I replaced the fuse, and the fuel pump relay, and it still was operating. I plugged in a known good pump, and sure enough, it kicked on. So, I replaced the fuel pump and filter, and sure enough, the car fired right up.

Now, I'm baffled as to what killed the pump. It was driving just fine before we did the tank, and I'm just curious whether it was a strange coincidence that the pump quit at this time, or if the wiring to the pre-pump is tied in with the main pump and something shorted out when the harnessing broke. Any ideas?

 

the two pumps might share a common ground point, I'm not sure.

the power wiring to them is completely different. the main pump comes directly off the fuel pump relay behind the glovebox, and the tank pump goes through the fuse panel.

i'm thinking this was just a coinkydink.