need electrical help bad
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need electrical help bad
i have lost all electrical power in side my 78 f150. no radio,lights, igntion, heater nuthing. put new soilnoid on today still nuthing. could the brain box have went out? i have not cut the fuseable connectors out yet was my next move but got dark on me today. any help would be appeciated.
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
The ignition module has nothing to do with in-cab power. Putting on a new solenoid was a waste of your money because it has nothing to do with the problem either. First check the battery voltage, then we can test the fusible links for continuity. Don't cut them out until you know they're bad!
When I say check the battery voltage, I mean actually check the battery voltage.
When I say check the battery voltage, I mean actually check the battery voltage.
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it will start but as soon as i let go to disingauge the starter so its not grinding it dies like the switch is in off postion. i had to replace inner and outer ignition swich but has been running since then so im pretty sure its not that. im really at a loss on this one
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
Have there been any modifications to your wiring? That doesn't sound right - when you jump the solenoid, the coil will have power, but I'm not sure the ignition module will have power to fire the coil. I could be wrong here, but all the diagrams I'm looking at show the power for the box while in start mode sourcing from the key.
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
Okay, I just went out to my truck, and confirmed. With a properly wired setup, the only way to get the truck to start by jumping the solenoid is with the key in RUN or START. Just jumping the solenoid without the key in the ignition won't do anything except crank the motor over. This is what I thought.
So, if you're able to start your truck by jumping it at the solenoid, something else is wrong. That means your ignition module is getting power without the key. That's what's happening isn't it? All of this is happening without the key in the ignition? That's what I was assuming, please correct me if this is not the case.
So, if you're able to start your truck by jumping it at the solenoid, something else is wrong. That means your ignition module is getting power without the key. That's what's happening isn't it? All of this is happening without the key in the ignition? That's what I was assuming, please correct me if this is not the case.
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no i had the key in the ignition and in the on possiton when it starts its just like the switch is in the off possion could the swich have went out? its not been in but maybe 3 months. it like the brain is not comunicating there is no power to my fuse panal at all. does the fuse pannal for the most part runs for the ignion power wire ? to start with when all this started you might start the truck 100 time today and the next time you trie it would have nothing you could keep trieing and it would start. there is no power to the igntion. im fair at wireing and stuff but this has got me thanks for your replie and help
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sorry been working alot lately yes i had the key on but let me catch you up on what i have found the fusable link was bad cut it out and replaced it with fuse found the ingnition switch plug burnt and busted in two replaced it. i have a wire that is red with green stripe that says do not cut or splice resistor that is getting very hot when the key is on. but now it will not start. it will turn over by the key
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ok got the truck to start today had to replace the brain box and coil. but hte red and green wire is still getting warm not hot i have traced wire all the way from switch to the coil and have not found any grounded spot any help would be appeciated the truck has external resistor on coil
MSEE
Joined: Apr 2004
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From: Austin, TX
The wire that says "do not cut" is the resistive wire for the coil. It powers the coil when the key is in RUN. Ignition coils pull a significant amount of current, so it's natural for this wire to get somewhat warm during operation, because the wire's resistance dissipates heat as current passes through it. This is why your coil says "external resistor," this long red wire is what they're talking about. Making the resistor a long wire like this makes it easier to dissipate heat than if it were a single element, like a blower motor resistor. However, it shouldn't be too hot. How warm would you say it's getting?
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yesterday when i was working on it before i changed brain box and coil it would smoke. after i changed brain and coil you can hold it in your hand for a long time. on the fuseable link i had to cut out i put in a fuse link what size fuse should i use i had a 15 amp and it poped i one time
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
With the coil hooked up, turn the key to RUN and measure the voltage between the BATT side of the coil and ground (unpainted metal on the engine). This will help determine how much current you're pulling through the resistive wire (it's a little high to run an ammeter in series, so to be safe we'll look at voltage instead). The smoking wire was probably a result of your coil shorting and pulling too much current; try to find any melted insulation because smoking meant something was burning off which is not good. I'll try to get out to my truck later and see how much my wire heats up too.
What wire do you mean for the fusible link? There are a couple; I'll have to check what's on mine. 15 amps is probably a little low because those wires feed most of your electrical system, depending on which one you're looking at.
What wire do you mean for the fusible link? There are a couple; I'll have to check what's on mine. 15 amps is probably a little low because those wires feed most of your electrical system, depending on which one you're looking at.