Perhaps you are drawing too much current with your pumps and any other electronics you have added?
You can determin the current while cranking by measuring the battery voltage with nothing on. Then measure it while cranking. As Mike 69 Cuda alluded to...
If the voltage drop during cranking is a lot then there is a lot of resistance to turning the engine over OR there is a large electrical resistance in the circuit.
If there is little to no voltage drop during cranking then the starter, starter Bendix, starter realy is not engaging correctly.
On a side note...
There should be a heavy gage wire from the battery directly to the starter.
There should be a second lighter gage wire from the starter relay to the starter Bendix. The starter relay DOES NOT pass high current to the starter like Ford starter relays do.