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Then follow the main positive lead back to the engine and down to the starter motor, and check the connection at this end as well. There should also be a small wire to the motor which should have 12V when you're turning the ignition switch to crank.
Check the resistance of the main positive lead that runs down to the motor as anything more than a few ohms and it should be replaced
Don't forget to try a jump start from another car / battery as its possible the battery is poor, if you have a voltmeter a healthy battery should read 12.7+V