My truck died completely,starts up after jump and dies down.the computer screen is blank .what could it be?
Even with a cheap multi meter, and little help you should be able to do some basic trouble shooting. Until some more specific information is obtained nobody will be able to say exactly what the problem is.
My guess is that your alternator is bad and have now taken out your batteries.
or your battery is just old and tired and doesn't have enough amperage to keep the car running. Like mrmoony said, check the voltage of the battery, anything under 12.2Volts and 5 years old, swap it out. then once you have the new battery, use that ,multimeter to check to see if the alternator is working. Start the car, and probe the terminals, should be around 14.5volts if everything is OK.
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