The battery has plenty of power and when the key is turned it clicks once but no starting or cranking

There are some things you can do to fix the problem. Check battery connections: Even if the batteries are charged, it is important to make sure the battery cables are clean and tightly connected. Components with loose or damaged wires can interfere with efficient energy transfer. Check fuse relays: Check the vehicle fuse box for any blown fuses or defective relays that could affect the starting system. Transmission Position Sensor: If your vehicle has an automatic transmission, the transmission position sensor (neutral safety switch) may not work properly, preventing the vehicle from starting into gear Start the vehicle in both park and neutral and check that is there any difference. Check for safety system problems: Some cars have safety systems that can shut down the engine if there is a problem. Make sure the security light on the dashboard behaves as it should and try to use a spare key if there is one. Starter Motor: The starter motor may be faulty. Turn the key and listen for the clicking sound. If you hear a rapid clicking noise, it could indicate a faulty battery or a faulty starter motor. Hearing a click once could indicate a problem with the starter solenoid. Ignition switch: The ignition switch sends power to the starter when the key is turned. If faulty, it can prevent the engine from cranking. Try to notice a change when you change the key. Fuel Supply: If the engine cranks but does not start, there may be a fuel issue. Check the fuel level and make sure the fuel pump is working properly. Check engine light: If the check engine light illuminates, a diagnostic trouble code (DTC) may be stored in the vehicle computer.

Check your battery leads - make sure they aren't corroded and have broken strands.

Also - in particular - check the cleanliness and tightness of the black earth cable where it attaches to the engine block/bodywork. The symptoms you describe can be caused by a poor earth connection.

As a quick check - attach a booster cable to the battery negative terminal and attach the other end to a suitable earth point (I.e.. a clean bolt..) on the engine block or bodywork. Try and start the car .. if it starts .. you have a bad battery earth

When the vehicle doesn't start, you will need to check the purple wire at the starter solenoid for power when the key is held in the crank position. If there is power during this procedure, the starter will be defective. If no power, possible ignition switch... neutral safety switch..starter relay ( if equipped ) or wiring problem

First off, you will need both batteries connected for the amperage to be available to start a diesel. Secondly, when you turn the key, the vehicle will not crank over? Does it make any sound at all? DO the power door locks work with the key fob?

have you checked power and signal at the starter motor, the large wire @ the starter will have battery voltage at all times and the smaller "signal wire" will have power only when the ignition cylinder is being cranked, if both ok then you will have a stuck/seized solenoid on the starter . lightly tapping the starter motor while "cranking " will sometimes allow the vehicle to start.

U might have 12 volts but no cranking amps try a jump start

could be the neutral switch try and crank it while moving the shifter around also try and put power to the small terminal on the starter that will tell you if the starter is bad or the wiring or switches

prob the starter

Battery or starter. Sometimes the battery will have enough power to activate fuel pump and dash lights but not enough to turn starter.

Did you try to boost battery? Sounds like low charge. Check battery terminals for tight and clean as well as groung connection at body and power connection at starter for clean. If battery OK test for power on starter wires. Large wire will have contant battery power small wire will have battery power when key is in crank position. If power ok on both it will probably need a starter. Hope this helps...Good Luck.