78 electrical problem
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New User
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78 electrical problem
hello everyone, im new to the forum but have been searching on here and other sites for a few days to find some help and checked all i found with no luck so maybe you guys can help.
i just got a 78 f150 ranger and it has no power anywhere. when i put a jumper from the battery to the hot side of the ignition module i get power. with out that nothing to fuse block headlights or ignition switch. when i jumper it i can jump the solenoid and the coil to start it then pull the wire off the battery and kill it. i have 2 wires off the solenoid i traced and one goes under the dash to a 3 prong plug that is yellow and looks like a trailer plug but nothing goes to it. checked the fuseable links and they're good, grounds are good.
i dont know much about wiring and it even has my buddy stumped and he has been working on old fords since he could walk.
really need some help because im lost. another friend said that jumping the way i did is back feeding the system and sending power to the wrong side of the fuses but i don't know.
any suggestions?
i just got a 78 f150 ranger and it has no power anywhere. when i put a jumper from the battery to the hot side of the ignition module i get power. with out that nothing to fuse block headlights or ignition switch. when i jumper it i can jump the solenoid and the coil to start it then pull the wire off the battery and kill it. i have 2 wires off the solenoid i traced and one goes under the dash to a 3 prong plug that is yellow and looks like a trailer plug but nothing goes to it. checked the fuseable links and they're good, grounds are good.
i dont know much about wiring and it even has my buddy stumped and he has been working on old fords since he could walk.
really need some help because im lost. another friend said that jumping the way i did is back feeding the system and sending power to the wrong side of the fuses but i don't know.
any suggestions?
Senior User
Joined: Nov 2015
Posts: 137
Likes: 1
From: FL & NY
Was it starting and running OK before the current no power problem ?
Sounds to me that you are not getting + 12 volts to the ignition switch OR if there is + 12 volts at the switch, the switch may be bad.
Sounds to me that you are not getting + 12 volts to the ignition switch OR if there is + 12 volts at the switch, the switch may be bad.
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i just got it Thursday. it was like this when i got it. guy said he drove it til it lost power, but my buddy doesn't think he ever did,he thinks i have complete harness missing but doesn't know. when i jump it it gets power to everything while its running but if not, i got nothing.
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New User
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thank you. that plug under the dash that runs to the solenoid is the one that has me most confused doesn't have a place to go in my truck.
Laughing Gas
Joined: Sep 2003
Posts: 968
Likes: 5
From: Corbett, Oregon
First, Hello and Welcome
to the site.
There are fusible links that supply power from the solenoid (+) to the truck. In an overload, or short circuit condition, these will open up and cause the problems you describe.
These fusible links look like regular wire, but they are undersized and designed to open under excessive load. Typically there are one or two that come off the (+) side of the solenoid. They are usually marked as a fusible link and their size. They are a one time act and should be replaced with the same size replacement link.
You will need to identify and fix the overload / short before replacing the link. Otherwise the problem will take out the new link.
My guess is that the previous owner made some change to the truck that caused the link to let go. Trailer wiring, new stereo, etc.
Use the search function here and you should find wiring diagrams and pictures that will help.
Chasing wiring problems is not difficult, but it does require a slow, comprehensive approach. Don't assume anything and prove out everything, one wire at a time.
Good luck.
to the site. There are fusible links that supply power from the solenoid (+) to the truck. In an overload, or short circuit condition, these will open up and cause the problems you describe.
These fusible links look like regular wire, but they are undersized and designed to open under excessive load. Typically there are one or two that come off the (+) side of the solenoid. They are usually marked as a fusible link and their size. They are a one time act and should be replaced with the same size replacement link.
You will need to identify and fix the overload / short before replacing the link. Otherwise the problem will take out the new link.
My guess is that the previous owner made some change to the truck that caused the link to let go. Trailer wiring, new stereo, etc.
Use the search function here and you should find wiring diagrams and pictures that will help.
Chasing wiring problems is not difficult, but it does require a slow, comprehensive approach. Don't assume anything and prove out everything, one wire at a time.
Good luck.
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New User
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First, Hello and Welcome to the site.
There are fusible links that supply power from the solenoid (+) to the truck. In an overload, or short circuit condition, these will open up and cause the problems you describe.
These fusible links look like regular wire, but they are undersized and designed to open under excessive load. Typically there are one or two that come off the (+) side of the solenoid. They are usually marked as a fusible link and their size. They are a one time act and should be replaced with the same size replacement link.
You will need to identify and fix the overload / short before replacing the link. Otherwise the problem will take out the new link.
My guess is that the previous owner made some change to the truck that caused the link to let go. Trailer wiring, new stereo, etc.
Use the search function here and you should find wiring diagrams and pictures that will help.
Chasing wiring problems is not difficult, but it does require a slow, comprehensive approach. Don't assume anything and prove out everything, one wire at a time.
Good luck.
to the site. There are fusible links that supply power from the solenoid (+) to the truck. In an overload, or short circuit condition, these will open up and cause the problems you describe.
These fusible links look like regular wire, but they are undersized and designed to open under excessive load. Typically there are one or two that come off the (+) side of the solenoid. They are usually marked as a fusible link and their size. They are a one time act and should be replaced with the same size replacement link.
You will need to identify and fix the overload / short before replacing the link. Otherwise the problem will take out the new link.
My guess is that the previous owner made some change to the truck that caused the link to let go. Trailer wiring, new stereo, etc.
Use the search function here and you should find wiring diagrams and pictures that will help.
Chasing wiring problems is not difficult, but it does require a slow, comprehensive approach. Don't assume anything and prove out everything, one wire at a time.
Good luck.
i used a tester and have power on both sides if the links in both wires.
they are.both hot as far as i can trace them
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5th Wheeling
Joined: Dec 2015
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Check the BLACK/YELLOW wire at the ignition switch for power. Its a direct feed off the solenoid thru a fusible link.
Tug on the fusible links, they may be burnt but touching inside the insulation. They will pass enough current to light a test light but not enough to do anything else. I chased that for a week.
You can register on Autozone's website and get the wiring diagrams for free.
Tug on the fusible links, they may be burnt but touching inside the insulation. They will pass enough current to light a test light but not enough to do anything else. I chased that for a week.
You can register on Autozone's website and get the wiring diagrams for free.
Thread Starter
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New User
Joined: Jan 2016
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Check the BLACK/YELLOW wire at the ignition switch for power. Its a direct feed off the solenoid thru a fusible link.
Tug on the fusible links, they may be burnt but touching inside the insulation. They will pass enough current to light a test light but not enough to do anything else. I chased that for a week.
You can register on Autozone's website and get the wiring diagrams for free.
Tug on the fusible links, they may be burnt but touching inside the insulation. They will pass enough current to light a test light but not enough to do anything else. I chased that for a week.
You can register on Autozone's website and get the wiring diagrams for free.
Postmaster
Joined: Mar 2011
Posts: 2,698
Likes: 7
From: Taxachusetts
Have you checked the battery terminals for corrosion around the connections? Get even a small bit of corrosion encircling the terminals and your connections and it'll act like insulation....lets just enough juice through to seem like the connections are good, but won't let enough current/voltage get by to fire up the engine.
Battery cables don't have any stiff spots along their lengths from A to B? ....they're flexible enough to bend easily?
Does your solenoid have a good, clean ground between it and the inner fenderwell?
Sure you have enough grounds, and connected in the right areas....Bat (-) to block and frame, engine to firewall, good cable to starter, good ground from alternator,....etc?
Brain box checks out ok?
Battery cables don't have any stiff spots along their lengths from A to B? ....they're flexible enough to bend easily?
Does your solenoid have a good, clean ground between it and the inner fenderwell?
Sure you have enough grounds, and connected in the right areas....Bat (-) to block and frame, engine to firewall, good cable to starter, good ground from alternator,....etc?
Brain box checks out ok?
Thread Starter
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New User
Joined: Jan 2016
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Have you checked the battery terminals for corrosion around the connections? Get even a small bit of corrosion encircling the terminals and your connections and it'll act like insulation....lets just enough juice through to seem like the connections are good, but won't let enough current/voltage get by to fire up the engine.
Battery cables don't have any stiff spots along their lengths from A to B? ....they're flexible enough to bend easily?
Does your solenoid have a good, clean ground between it and the inner fenderwell?
Sure you have enough grounds, and connected in the right areas....Bat (-) to block and frame, engine to firewall, good cable to starter, good ground from alternator,....etc?
Brain box checks out ok?
Battery cables don't have any stiff spots along their lengths from A to B? ....they're flexible enough to bend easily?
Does your solenoid have a good, clean ground between it and the inner fenderwell?
Sure you have enough grounds, and connected in the right areas....Bat (-) to block and frame, engine to firewall, good cable to starter, good ground from alternator,....etc?
Brain box checks out ok?
will give updates then and pictures if it will load them.
thanks for the info.
Postmaster
Joined: Mar 2011
Posts: 2,698
Likes: 7
From: Taxachusetts
Maybe you did, I just didn't understand.
Have you tested the solenoid....they can be temperamental as an ex- wife.
Could be open on the inside - magnet could have developed an open for some reason, not closing and not allowing the juice to flow from the S to I termnial, to the starter termninal. Beat on it for a bit - see if you get anywhere. (The answer to all vehicle/life's problems - take the BFH to it).
If it was shorted, it would always run, or depending on the battery's health, you'd get that kkkklllllllllllliiiiiicccckkkkk sound. (Again, take the BFH to it...or the plastic end of a screwdriver).
You have a neutral safety switch (NSS) and is it in good working order?
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New User
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Have you tried jumping the solenoid from the S termnial (The one closest to the battery) to the starter cable? The solenoid needs/wants a good ground to do it's thing.
Maybe you did, I just didn't understand.
Have you tested the solenoid....they can be temperamental as an ex- wife.
Could be open on the inside - magnet could have developed an open for some reason, not closing and not allowing the juice to flow from the S to I termnial, to the starter termninal. Beat on it for a bit - see if you get anywhere. (The answer to all vehicle/life's problems - take the BFH to it).
If it was shorted, it would always run, or depending on the battery's health, you'd get that kkkklllllllllllliiiiiicccckkkkk sound. (Again, take the BFH to it...or the plastic end of a screwdriver).
You have a neutral safety switch (NSS) and is it in good working order?
Maybe you did, I just didn't understand.
Have you tested the solenoid....they can be temperamental as an ex- wife.
Could be open on the inside - magnet could have developed an open for some reason, not closing and not allowing the juice to flow from the S to I termnial, to the starter termninal. Beat on it for a bit - see if you get anywhere. (The answer to all vehicle/life's problems - take the BFH to it).
If it was shorted, it would always run, or depending on the battery's health, you'd get that kkkklllllllllllliiiiiicccckkkkk sound. (Again, take the BFH to it...or the plastic end of a screwdriver).
You have a neutral safety switch (NSS) and is it in good working order?
Postmaster
Joined: Mar 2011
Posts: 2,698
Likes: 7
From: Taxachusetts
I know you've probably heard it all before and by now you're are tired of explaining it..... but do you have the right brain box (module) - it would be the blue one.....And have you checked it to find out if it's still good?
From what side of the module are you jumping it - the input (Cab/firewall side) or the out put - going to the harness(es) side? ( I'm just trying to back trace wires here).
And the coil ohms out good, with snug fasteners, etc?
I'm wondering about the health of your ballast resistor wire.....
From what side of the module are you jumping it - the input (Cab/firewall side) or the out put - going to the harness(es) side? ( I'm just trying to back trace wires here).
And the coil ohms out good, with snug fasteners, etc?
I'm wondering about the health of your ballast resistor wire.....