we've checked the battery and changed the cable heads
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2002 GMC Yukon Question: my car wont turn over.
Answer #1patrick mannion from Greg Solow's Engine Room, February 02, 2012, 23:36Master
Do the head lights come on and shine brightly? If so the battery is probably OK. Do the dash warning light come on when you turn the key to the ignition on position, if so the ignition switch is likely to be getting power and transferring power. Ignition key in the start position check for power at the small wire at the starter, it will only have power when the ignition key is turned to the cranking position, if it has power under this condition it is likely a bad starter/starter solenoid.
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Replyglobalhelper, February 03, 2012, 05:53Master
yes ck your lights. there is a bulk loom of grounds at that rear of the p/s intake by the dist. that could be loose or corroded ck those