drove the 412 to work this morning... ran great. this afternoon, i had to pick up the daughters and drive the 20 miles home. 19 miles into the trip and going up a 6% grade the fuel pump just flat shut off checked fuses, looked in the engine compartment, pounded my head on the ground... nothing! and the 6 month old started screaming cried a little bit and then tried the car again and the pump started running. no biggie if i am by myself, completely unacceptable with 2 small children in the car.
Notchback mid-engine speedster Little Giant Killer 3
I'm no expert, but until one of the gurus jumps in, here's what I'd do. Check wiring to pump looking for poor connections, frayed ends, bad grounds, potential shorts, crimps, pinches, etc.. Fix/replace anything questionable.
Nothing? Then I'd be looking to make it fail again and see if I could learn anything. Weather? On a hill? After a hard run? We need a hint.
This can be caused by several things. Most usual is the two wire plug on the fuel pump it has a habit of getting wet (even with the rubber boot intact) and getting corrosion on the terminals. Vibration can cause intermittant loss of contact.
Next, is loss of ground to fuel pump relay or of the + side due to vibration in loose wires.
Lastly...and this is something to look at, you note that you were on a grade. A 6% grade can be pretty steep....depending upon what length it is 6% of... . If you have crud in the bottom of the tank...it can shift back and clog the sock filter. It doesn't actually cause the pump to stop but you do lose pressure. What happens is that then you sit still for a while and the fuel draing back through the line unclogs part of the sock filter...and you can run again. Ray
the 6% has been travelled several times. way back when i bought the car (non running, bad fuel pump) i pulled the nasty sock out of the tank and finally i had 3/4 tank fuel. it was just weird. haven't been able to replicated it again. thanks for the ideas guys... i will continue to chase the issue.
Notchback mid-engine speedster Little Giant Killer 3
I will agree with both of you guys on your comments. on my 73 412 sedan i ran into the same thing and the problem wasnt with the connections or grounds (not that they needed a good cleaning anyway) but my problem was the sedement and loose rust in the tank. what happened was in my situation pretty much the same with the up hill grade thing the same and the sedement would start clogning the filter sock in the tank and would cause the fuelpump to excessivly draw more amperage to suck the fuel through until it would trip the fuel relay and cause it to shut off for a moment. then a few minutes later it would start back up again. you gotta remeber that those fuel pump relays are rated to not let the fuel pump exceed a bit more amps from the system. so its doing its job by not prematurly burning out the fuel pump. It being a 20+ something year old car you better believe you got some kind of sedement in the tank. I was also thinking that the return line can cause a problem similar to that if the line is obstructed. That too will cause the fuel pump to strain itself and make the relay shut the fuel pump off for a moment.
Ah! Thank you for making that connection. If the voltage starts to drop to the fuel pump or fuel injection systems...amperage rises. If for some reason voltage is low....the draw ofr the pump may trip a relay. Ray
checked fuses, looked in the engine compartment, pounded my head on the ground... nothing! and the 6 month old started screaming 
cried a little bit and then tried the car again and the pump started running. no biggie if i am by myself, completely unacceptable with 2 small children in the car.
. If you have crud in the bottom of the tank...it can shift back and clog the sock filter. It doesn't actually cause the pump to stop but you do lose pressure. What happens is that then you sit still for a while and the fuel draing back through the line unclogs part of the sock filter...and you can run again. Ray