I assume you have replaced multiple times, so the solenoid should not be the problem. Most are controlled by the ECM, negative wire and have a constant positive. Make sure the wire going to the ECM for negative has a good connection. Check battery voltage using the connection at the block and see what your voltage drop is. Do the same with the battery connection at the solenoid, check battery voltage at battery post and at solenoid, what is the voltage drop. Anything more than a couple of tenths needs to be repaired. If it is mounted to close to a heat source can also make it fail, need a heat shield. On a diesel engine, may need to add ground wire from injection pump to engine ground. Have also seen when engine has repairs completed, ground cables have been removed and not installed when repair is complete. Hope this helps.