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Hey guys so Ive always had troubles starting my truck in the cold, every once in a while i would have to hook the battery booster to my battery to get to work in the morning. Had the same issue happen just the other day so pulled out the booster and had no luck getting started. Came home later that day an the truck started right up, cool right? So the next morning i went to go start it got 2-3 cranks and it fired..... then everything went dead, engine, dash lights( oil, battery,brake indicator lights) now when i turn the key i get absolutely nothing, nothing turns on, no crank no nothing. i checked my battery and it was around 12.5 volts, pulled my spare out and it read about the same but i get nothing what so ever with either battery installed. im guessing Ive got a short somewhere but im not to sure where to start. Thanks for any input


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Battery cables are loose or dirty connection, so only work some times. Jumping always connects to the cables so that always works. While cranking the engine over hundreds of amps pass through he battery terminal/cable connection. If the connection is weak it will pop like a fuse and then you have nothing.


Clean and tighten the cable to terminal connections. If they are badly corroded... replace the ends.

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So Ive cleaned the clamps and tested the battery itself with an ohm meter, all seams to check out, Ive got a light tester, with positive hooked up and the negative unhooked i run the light tester to the battery negative terminal and the negative cable and i get light, which i find weird. and i do the opposite, hook the ground up and unhook the positive and run the tester between the the battery positive terminal and positive cable and it lights up, which is the way Ive understood how to initially check for a short. So my positive has one big cable running straight to the starter, and one bolt on "plug" to what im assuming is everything else. with that plug, unplugged im still getting a light on my tester. which to me tells me the starter has a short which would make sence why i dont get a crank but that doesn't explain why i get nothing anywhere else

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  i checked my battery and it was around 12.5 volts, pulled my spare out and it read about the same but i get nothing what so ever with either battery installed. im guessing Ive got a short somewhere but im not to sure where to start. Thanks for any input


Missed this part.


Won't be a 'short'. A short is a path to ground around any electrical device that you want powered. A 'short' path to ground would discharge the battery uncontrollably causing hot wires, smoke  and the real possibility of a fire. When something electrical fails to work it's almost always an 'open' of disconnection. A loose connection, a blown fuse.


Assuming that the battery and the cables are OK then this leaves the fusible links. You will find them connected to the positive cable near the battery terminal. The 720 has two Green and one Black fusible links. They are about 4" long and have plastic connectors on the ends for easy removal/replacement. Check yours for being crispy melted or burnt looking as they are in fact a form of fuse.



If you have the door open, a clock or a stereo this may explain the draw. Pull all the fuses one at a time and see if and weather the lamp goes out. The fuse that causes this is the circuit with the draw. A short would blow the fuse.

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Having had this happen repeatedly on various 720s, if battery checks out there is a very high likelihood Mike is right and one of your fusible links has burned out. I've had it happen at least once on 3 different 720s.

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Alright thanks mike, to start easy i went ahead and pulled all fuses (inside and under the driver side dash) and the lamp never went out so that ones up in the air. With the fusible links is there any way i could get a picture of what your talking about? im a little unclear of what the links would be. And you say they're like fuses so is that something i could go down to the auto parts store and replace fairly easily?

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Look at your positive connection on the battery. There are multiple wires coming directly from there. Some green and a black. These wires are about 4 inches long then have a white connector on them. Those white connectors connect to other color of wires.


You want to look at those green and black wires right off the battery. I will try to find a pic.

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See the black and green wires coming off the positive battery post with the black plug on one end and the white plugs on the other, the black and green wires are the fusible links, my diesel has 4 of them, your gas truck likely has 3 wires.

If you feel the wires, and feel no wire inside, then it likely is blown, you can test each one by unplugging the white plugs and then test for power at the white plug end.

Also try wiggling the black plug, it some times makes a bad connection.

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Isn't the bigger issue here what is causing the fusible link to fry. They are designed to melt if too much current flows them. Lots of current causes heat. This protects the components in your vehicle from getting to hot and burning down your truck. If you slap another fusible link in there and it burns up again because you have a short your right back were you started.


Figure out what circuit is fed by said fried fusible link and look for bad wiring that has grounded out, then install new fusible link

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Age slowly frays those wires until there isn't enough left to carry the intended load and they burn the rest of the way.


I would replace it, have another on hand, and see if it burns immediately.

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wayno, yes 4 for the diesel and 3 for the gas engines.




There are 3 fusible links. A Black and a Green together and a separate Green one.


The separate Green one powers the headlights.


The other Green one powers the ignition switch...

The Black one  powers several things on the fuse box horn, brake lights



If you have no headlamps, (Green) no horn, (Black) no starter (Green) then probably not the fusible links. They can't all be burned out. Back to the battery cable. Check the ground connection on the intake manifold.

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So just to be sure about my main connections i pulled all of them sprayed them with some cleaner and took sand paper to them. With everything hooked up like it should be i still get nothing, so just for kicks i unhooked my starter cable from the clamp, and what do ya know!? i got dash lights, head lights ect. Cool i thought till i hooked the starter cable back up and boom everything is dead again, so with my starter UNhooked i get power and a voltage reading from the battery....hook the starter back into the loop and everything goes dead, no power and a reading of 0 volts from the battery???? So did my starter take a dump on me?                               

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So im not sure exactly what i did to fix it (for now anyway) but since it seemed to be my starter causing the problem i pulled it off tore it apart cleaned all contacts and connections, (didn't see anything noticeably bad) slapped it back together put it in and tried my "short" test, and... no light, so that's a good sign. So i went ahead and tried it and she fired right up. Thats awesome for now but like i said, im not really sure how or what i did to fix it :blink:  Thinking in the near future just getting a new starter 

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When you pulled the starter, you likely pulled the positive cable off the battery, you likely could have put it right back on without pulling the starter and all would have been good, you likely had a bad connection at the battery, some times that happens when the posts/cables get corroded/dirty.

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disconnect the T and + side connector toalternator and see if light goes out/ Maybe a diaode is shorted. But that would kill a battery in a day.


clean contact of battery also as mensioned

can I cut that t connection off and splice the wires together and just hook them directly to the positive post using a standard connection?
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The T connector has two wires.


One (the top of the T) goes to the dash red lamp to indicate if charging or not.You want to leave that one alone.


The other, the I part of the T finds it's way back to the positive terminal through the Black fusible link. I can only assume this is to protect the battery from an over charge condition or a possible grounding of the charge wire.


ALL electrical wiring circuits should be on a fuse in the fuse box or run through a fusible link to protect against fire.


Worst case scenario.... an accident that crushes the wiring to the body producing a short circuit and maximum current flow. Without a fuse to blow and break the circuit the wires will heat up like the inside of a toaster. Your choice.

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