720World

Little Trucks, Big World

Wondering if they worked any different in different years. My '85 doesn't pump with the key switch turned to on, have to hold it over toward start  a little to hear it work. My newer to me '83 works and keeps working with key in on position.

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Worn ignition switch???

How exactly are they supposed to do?

Well I was under the impression that the relay was like a delay timer. If certain conditions were met the relay stayed on. If something happens ... like the engine stops (here the alternator stops charging and eventually the oil pressure light comes on.. both are inputs to the relay) then the timer times out and the pump stops. 

Lets say the timer is 10 seconds long. Turn ignition to on, timer starts and fuel pump is on.... but you don't start. In 10 seconds the pump shuts off because you are not using it. You turn the starter on and start truck. The starter is an input and the timer starts again. Well before the 10 seconds ends the engine is running and alternator starts charging and the oil light is off so the fuel pump keeps running.

It would seem that if the alternator should stop charging OR the oil pressure should drop to zero, the timer would time out and the pump stop.

This would protect your engine from lack of oil pressure and also in an accident where there may be fire involved. Pump shuts off without your input. You may be unconscious and upside down in the seat belt.

I don't know if this is how it works but some of these elements probably are close at least.

Thanx Mike. Hoping someone with one up going would try theirs.

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