Electrical gremlins

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This Bad Demon

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Good night. I have an electrical question. Ok I have a 1972 Dodge Demon. I bypassed the ammeter in a fashion similar to the MAD bypass. I've been running the car for about 2-5 months like that....Here lately I'm blowing the fuse I have in line. When I start the car and give it gas it will blow. Sometimes it doesn't. I put a volt meter on it an voltage bounces from 12.5 to 14...when I rev it to 2000 grand it goes up to 14.3 and is pretty steady there...May jump to 15. I have replaced the alternator thinking that it was shorting out...That didn't fix it. The car has MSD ignition and Fast Ez efi on it. Anyone have any ideas?
 
If you replaced a fusible link with a fuse, that would be the first thing to change back; but it will have to be the correct size for all the new loads.
I love relays, and use them wherever I can, and I use all the same kind, so they are swappable.
Now to answer why she is blowing the fuse; IDK.
But I hope you are not running an electric fan through the bulkhead connector and I hope it is running on an automatic controller.
The ignition should also be on a relay, as should be the EFI.And anything else that pulls more than a couple of amps.Like a fuel-pump....
But I'm pretty sure that you probably already wouldof done all that............
 
What amp fuse is inline?
Volts don't mean squat really when it comes to fuses, amps do and if you are running less than a 30 it doesn't surprise me that it blows.
Main fuses in some cars are 50 and 60 amp.

I think what is happening is when you start the car it draws the battery down a little and when the car starts it tries to replace that used power from the battery and blows the fuse because it's too much amps for the fuse to carry.
ESPECIALLY if it usually only blows on startup and not any other time.
 
If you replaced a fusible link with a fuse, that would be the first thing to change back; but it will have to be the correct size for all the new loads.
I love relays, and use them wherever I can, and I use all the same kind, so they are swappable.
Now to answer why she is blowing the fuse; IDK.
But I hope you are not running an electric fan through the bulkhead connector and I hope it is running on an automatic controller.
The ignition should also be on a relay, as should be the EFI.And anything else that pulls more than a couple of amps.Like a fuel-pump....
But I'm pretty sure that you probably already wouldof done all that............

Thanks for your reply...I'm slowly getting around to doing relays...I've just been in the process of breaking in the engine and the minor things of making it a driver. No electric fans. Everything is stock minus the wiring I did. It's been running good for the time I said. Only recently started popping the in line fuse. That's the electical ghost I'm chasing.
 
What amp fuse is inline?
Volts don't mean squat really when it comes to fuses, amps do and if you are running less than a 30 it doesn't surprise me that it blows.
Main fuses in some cars are 50 and 60 amp.

I think what is happening is when you start the car it draws the battery down a little and when the car starts it tries to replace that used power from the battery and blows the fuse because it's too much amps for the fuse to carry.
ESPECIALLY if it usually only blows on startup and not any other time.

Thanks for your reply. Currently the fuse rating I'm using is 30 amp...It's been running good for the time I said. Only recently started popping the inline fuse. Sometimes on start up...Sometimes it blows when I rev up the engine...Sometimes it don't....I drove it to work..No problem. Reach home turn it off...Wait a couple seconds. Start it and the fuse has blown..Sometimes that doesnt happen...My headlights also stopped working only the parking lights working (thinking that's the switch).
 
It could be a pinched or stripped wire that occasionally makes a short to ground. Those are a nightmare to find.... You have to hand trace each wire and inspect it. I would pull any panels you had loose, and look for a pinched wire first. If it was pinched it may have taken a while to wear through the insulation. Which could be why it just started doing this. Good luck!
 
Voltage regulator or its chassis ground would be my guess.
 
There should not be a fuse, able to shut down the engine. If everything shuts down, then the main circuit is being interrupted, and it should not be fused; but F-linked. The Fusible link makes it possible to have short-term power overloads, yet not cause an F-link meltdown, or a blown fuse.
Of course it could just be a sloppy connection at the back of the ammeter or the ignition switch. Or the bulkhead connector. Or the ballast resistor, or a faulty coil, or a bad splice, or a loose connection at the starter relay. or a bad engine ground. 'Cuz that is the main-circuit.

But really you never said WHAT fuse it is blowing.....................
Is it the one that powers up the EFI?, or
is it the one that powers up the MSD?, or
Is it the one that powers up the fuel pump?,or
is it the entire main circuit?
Do you have one fuse doing all those jobs? and are they all powered through the ignition switch?

But the thing that confuses me is that you say you reached home on a running engine, shut it off, and then it will not restart,because of "a" blown fuse . Does that mean it will not crank? Or it cranks but will not start.
If it cranks but will not start, then it seems to me you will have to figure out which circuit is overloading the fuse;either the pump, the EFI, or the MSD, or quite possibly something else.Since we have no clue how you wired it, we really have no clue where to start the diagnoses.
But Ima gonna guess that the fuse cannot handle everything that is used during the starting procedure; such as the above three plus perhaps the brakelite circuit if you are standing on it, plus the starter relay, etc
or relayed with separate switches
 
There should not be a fuse, able to shut down the engine. If everything shuts down, then the main circuit is being interrupted, and it should not be fused; but F-linked. The Fusible link makes it possible to have short-term power overloads, yet not cause an F-link meltdown, or a blown fuse.
Of course it could just be a sloppy connection at the back of the ammeter or the ignition switch. Or the bulkhead connector. Or the ballast resistor, or a faulty coil, or a bad splice, or a loose connection at the starter relay. or a bad engine ground. 'Cuz that is the main-circuit.

But really you never said WHAT fuse it is blowing.....................
Is it the one that powers up the EFI?, or
is it the one that powers up the MSD?, or
Is it the one that powers up the fuel pump?,or
is it the entire main circuit?
Do you have one fuse doing all those jobs? and are they all powered through the ignition switch?

But the thing that confuses me is that you say you reached home on a running engine, shut it off, and then it will not restart,because of "a" blown fuse . Does that mean it will not crank? Or it cranks but will not start.
If it cranks but will not start, then it seems to me you will have to figure out which circuit is overloading the fuse;either the pump, the EFI, or the MSD, or quite possibly something else.Since we have no clue how you wired it, we really have no clue where to start the diagnoses.
But Ima gonna guess that the fuse cannot handle everything that is used during the starting procedure; such as the above three plus perhaps the brakelite circuit if you are standing on it, plus the starter relay, etc
or relayed with separate switches

Thanks for the reply. As I stated in the beginning of the thread I bypassed the ammeter in a style similar to the MAD wiring schematic. The fuse that keeps blowing is the one that's inline with the wire attached to the battery stud on the alternator running to the starter relay. When it blows the car will not crank...I have the msd and ez efi on separate switches until I put them on relays. I have been running the car for 2-5 months how it's wired now.
 
Yeah that's about the 2nd worst possible place to put a fuse. But blowing a fuse there should not shut the vehicle down.Since it at least seems to prevent a restart,( whether cranking or firing or fueling you haven't told us yet), I think it's time to revisit the wiring diagram.
Unless the battery is very low or dead,and it's a no crank situation; which still does not involve that fuse as to starting.....
But, I might speculate;
If the battery is low to start with, then the alternator could go into overdrive right after a successful start, and if the fuse is unable to pass the juice, it will pop. And if you are not watching the voltmeter, you may not catch the popping until you return to home.
Since the alternator output is somewhat dependent on engine rpm, it might not pop the fuse until 30 plus mph, depending on your driving style.
 
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Good night...I believe I found the problem...After work yesterday I come home and took a look at the volrage regulator connector and the wiring on the fire wall....Come to find out the blue wire with the Fusible link attached came loose from the connector. I put it back in and started the car and no pop of the fuse and the charging voltage return to normal...Rev the engine...no pop....Didn't get to drive it because it started to get dark and my headlights are not working and getting ready to deal with this hurricane that's coming.....Question...What could I use to keep that wire from slipping out again?
 
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