Q: my ground cable at the battery gets hot,the speed odometer jumps up and down on 2001 Ford Ranger

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the motor doesn't idal right.when you mash the breaks the dash and headlights will go deam and bright like a weak battery.the speed odometer jumps up and down.the ground cable at the battery gets hot quick too.
(2) Answers
Agree with #1.... Also check ALL the wires coming from the neg battery cable end to see if their connections are clean and tight. Especially the one that goes to the truck body!... Check charging system also.
Start by cleaning both battery cable terminals and battery posts, apply a light coat of dielectric grease, then re-install your battery cables. Complete a drive cycle so your engine control module can re-learn the fuel trim parameters, and immediately check the cables to see if they are getting hot still. The cable that is still getting hot should be replaced if the post clamp is stretched and not making good contact.