12 volts
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Freshman User
Joined: Apr 2007
Posts: 39
Likes: 0
From: huntington
12 volts
i have a 78 f150 4x4 351m and it wont start i have replaced the brain box and distributor , coil and i noticed that when i unplug the negitive side of the coil i have 12 volts but as soon as you plug it in it goes to 7.5 volts this cant be right / right so thats why i replaced the parts . there not that expenseive compared to the headache . but this didnt work . any sugestions .
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
No, that all sounds right. With the negative side of the coil disconnected, there is no voltage drop across the coil resistive wire and the primary winding since no current flows, so you'll see 12. With it connected, current flows and voltage will distribute across the coil resistive wire and the primary winding, and 7.5 is around the ball park that you will see at the coil. I am sorry to say this but you wasted your money. Have you checked the resistance of the pickup in the distributor? I don't have the numbers here with me but Autozone's website does have a pretty decent Duraspark troubleshooting guide with specs.
