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Need help with an electrical issue.

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So I own an '80 720 and had just replaced the battery. After I replaced the battery and hooked the cables back up I took the truck for a quick drive. As I was about a mile away from home on the return trip I noticed the engine woulda lug a little bit and the throttle would start to get hard to push. After a few seconds I noticed some smoke coming from under the hood so I pulled off to the side of the road and opened the hood. A couple of wires next to the throttle cable had caught on fire and the throttle cable itself was glowing orange and extremely hot so I blew out the little bit of flame there was and gave it a few minutes to cool down. Now after the throttle cable had cooled down I had no other choice but to starte the truck and drive the last mile home. As soon as I started the truck and began to take off the engine started to bog down so I pushed the throttle down and it got stuck and the engine started to race so I just kept going. As soone as I pulled into my driveway smoke started to appear from under the hood so I shut the engine off and the engine kinda sputtere a bit until it finally stopped. I blew out the flames and pushed it the last twenty feet and parked it. Now at this point I probably should have removed the battery, but like an idiot I left it connected. This all happened around 3 PM. Nothing else happened after that. The next morning around 9 my dad woke me up and told me there was smoke coming from the truck. So I ran outside(no shoes on of course and totally demolished my feet on sharp rocks and pinecones and what not) and opened the hood while my dad readied the fire extinguisher. Now as I opened the hood I noticed multiple wires in the engine bay were on fire and once again the throttle cable was glowin orange and had melted through a hose. After we put the flames out I disconnected the battery. Now I'm not very mechanically inclined but with the proper instructions I can do plenty. The question though is what could have caused this and what all do I need to replace to get it running again? Id like to do this myself since I can't afford to have a mechanic fix it and I don't want to get rid of the truck. So if anybody could help me out with this it would greatly be appreciated.

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Your battery is going to ground through your throttle cable beacause it isn't connected to ground through the frame and the engine block.  You are missing a good ground connection, hope you haven;t burned up too many other pseudo ground paths.  I'm sure many other gurus will chip in with your model specific wires to check and corrective actions, all I can offer is "good luck" and don't give up too soon.  720s are by no means my area of experience.

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It means that the positive terminal on battery or cable is rubbing against the body or frame.  Could be the hood coming down on the terminal or the positive cable is frayed and bare. Additionally there should be a ground wire from the negative cable to the body to help prevent this. As it is now the only path to ground from the body is down the throttle cable.

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I thought that may have been part of the problem. When I got the new battery it looked a little bit taller but when I would close the hood it didnt seem to be touching. Even if that was the problem would having agood ground have helped?

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I thought that may have been part of the problem. When I got the new battery it looked a little bit taller but when I would close the hood it didnt seem to be touching. Even if that was the problem would having agood ground have helped?


Well the good ground would have provided an easier path to ground than the throttle cable. Still would have heated it up but unlikely the carb would have caught fire. Battery may have been discharged or part discharged depending if you noticed the problem and raised the hood. Lets just say the damage would likely have been lighter. Here's my story...


Driving home one night early morning (not all that sober) and turned a corner, battery not tied down. It fell over, unknown to me and the positive post rested against the frame. Electricity always finds the shortest path to ground and as the motor has the ground strap on it, and it's on rubber mounts, rubber transmission mounts, leaf spring rubber bushings, shocks rubber bushings and rad hoses are rubber, it's insulated except for the throttle cable.  It stopped, and caught fire. I righted the battery and threw dirt on the flames to put it out. It fired right up but the gas peddle was frozen solid. The wire inside melted the plastic sheath and when it hardened....


So with 15 miles to get home I held the gas down by hand and set the fast idle cam to rev it up and away I went. Top speed was 30 in second and I was pulled over by the police. I explained what happened and he helped by following me with his flashers on. True story.

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