64 barracuda fusible link

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Dana

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64 barracuda owners, do you have a short green fusable link coming from the starter relay? If so where does it go? Into the bulkhead connector? Thanks
 
Yes, it would go into the bulkhead. Cavity "G"...
Jim the G slot is the hot wire coming from the starter relay. It doesn’t make sense to me why they would have a solid hot wire and a fusible link also.?
 
Jim the G slot is the hot wire coming from the starter relay. It doesn’t make sense to me why they would have a solid hot wire and a fusible link also.?
The fusible link is undersized section of a specific length to create a fuse that can tolerate short periods of higher current.
If the whole run was undersize, it would create excessive resistance during typical use.

I dont have a '64 FSM but typically the main wire is 12 gage and the fusible link is 16 gage.
If the battery is a little low when recharging begins, the battery may draw 20 or 30 amps for a minute. The 16 gage wire won't have a lot resistance to that, and will only heat up slowly. As the battery recharges it draws less and less current. So within a minute or two the current is down to 10 amps and the 16 gage can easily carry that with minimal resistance.
On the reverse situation, alternator dead, its possible to drive for hours on battery alone. Even with the headlights on, the fusible link will only cause minimal resistance. It's not ideal - it may get a little warm - but not going too many hours at night on battery alone anyway. LOL been there...

One situation where the power circuit can get pushed to where it gets damaged without immediately failing is recharging a nearly dead battery with the alternator.
 
The main job of the fusible link is to open if the battery is accidently grounded.
For example if the insulation on the main feed to the headlight switch rubs off against a sharp edge under the dash.
upload_2020-1-21_8-50-21.png

The link will turn to smoke almost instantly.
 
The main job of the fusible link is to open if the battery is accidently grounded.
For example if the insulation on the main feed to the headlight switch rubs off against a sharp edge under the dash.
View attachment 1715456290
The link will turn to smoke almost instantly.

That is misleading. The fuse link does not blow if you actually ground "the battery." A better statement might be that the link will blow if some main feed in the harness is grounded. The reality is, the fuse link is damn poor protection, I will relate "an annoying story from the old days"

In the early 70's I was stationed at NAS Miramar, and my perfectly good 70 440-6RR got rear ended. While it was being "fixed" I was given a junker loaner by McCune Chrysler Plymouth. One cold morning I had started the loaner Valiant, complete with bald tires, and the Chief came in with his Columbo act........

"Del," he frowned and knitted his eyebrows, "I just have one question? Is your car supposed to be squealing and smoking?"

The alternator had stopped, and the worn belt was slipping and smoking. I shut it down, and not knowing A DIODE HAD FALLEN INSIDE THE ALTERNATOR, loosened the belt to examine. When I moved the pulley, the movement SHORTED THE DIODE. I got to sit there and watch the entire underhood harness go smoketypoo..........fizzzzzz'nnnnnszzzzzzzzsssssspppppttttttttttttttttttttttttttttttttttttTTTTTTzzzzit!!!! AND THEN BLOW THE FUSE LINK

So I called the dealer and told them to send a tow truck and another loaner car. Instead, they sent the wetback with a beat up pickup truck and some jumper cables.
 
This is the infamous MAD electrical article, and is a great simplified diagram of main power

Catalog

amp-ga18.jpg


NOTICE that the fuse link takes all battery power except to the starter, and feeds it through the bulkhead, through the ammeter, and to the under dash welded splice. It branches off from there and goes back out to the alternator, taps off to the fuse panel, the headlight switch, and the ignition switch. NONE OF THESE ITEMS JUST MENTIONED is protected by any fuse whatsoever, only by the fuse link

NOTE I tend to think in functionality instead of electron flow. So when I say "it goes from the battery to whatever" this is just the path, not electron flow. Some on here take issue with that. I grew up in the age of vacuum tubes, and understand neg-to-pos electron flow perfectly well
 
A better statement might be that the link will blow if some main feed in the harness is grounded.
I agree 100%

My point was the fusible link is to protect the main circuit from the power stored in the battery if its given a direct path to ground. That load will be very high - whatever the wires can carry, certainly a 100 amps or more. That's what it takes for the fusible link to melt quickly.
If any of the wires in the main harness are grounded, the link will melt in seconds.
Of course if any of the wires or connections between battery positive and grounding point are in poor condition - they may go first. :(
 
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This should interesting, went to move the '65 Valiant Signet convertible from one end of the back yard to the other and the motor died. Now everything completely dead, no lights, no starter, no nothing. Looking at the fusible link at the solenoid, it appears someone in the past may have replaced it with a plain old wire. I did not smell or see any burning/melting wires when the vehicle shut down, which I hope is a good sign.

I also noticed after sitting for so many months now, the master cylinder is devoid of brake fluid. Won't go under its own power and now won't stop either--have my work cut out for me this Spring.

Signet convertible.jpg


Signet motor 273.JPG
 
This should interesting, went to move the '65 Valiant Signet convertible from one end of the back yard to the other and the motor died. Now everything completely dead, no lights, no starter, no nothing. Looking at the fusible link at the solenoid, it appears someone in the past may have replaced it with a plain old wire. I did not smell or see any burning/melting wires when the vehicle shut down, which I hope is a good sign.

I also noticed after sitting for so many months now, the master cylinder is devoid of brake fluid. Won't go under its own power and now won't stop either--have my work cut out for me this Spring.


I think you lost your ground.
 
It’s possible you ammeter failed . That happened to me , I just went under the dash and unscrewed one terminal of the ammeter and moved the wire to the other terminal thus bypassing the ammeter and I was on my way . Been that way ever since the mid 80’s .
 
Update for post #10:

Cleaned battery terminals and I added additional ground using my jumper cables-no change. I added a permanent additional ground wire from battery negative cable terminal to radiator support--no change. I removed the wires to the ammeter and bolted them together--no change.

I checked for continuity for the under hood fusible link--checked out OK. I checked for power to the tail/stop light fuse--checked out OK (current available there). I checked for power to the cigar lighter fuse--checked out OK there. I checked for power to the cigar lighter--checked out OK there. I checked for power to the brake light switch-checked out OK there.

But we still have no headlights, no brake lights, no horn, no power to the positive side of the coil, no starter motor action using the ignition key. Everything dead as a door nail.

I used a remote starter switch connected to the starter solenoid under the hood and the motor cranked over! I pulled the wiring plug from the ignition switch harness (key) and the red hot wire had current coming from the battery. But turning the key to the "on" position resulted in no voltage at the coil. I checked the ballast resistor for continuity--checked out OK there.

I replaced the underhood wiring harness with an aftermarket one (I was not pleased with it and had stored away for a rainy day). This harness did not include the front lighting harness so I had to to remove the factory black tape the secured the front lighting harness and the underhood harness together (see photo).

The original ignition switch kept getting "stuck" during my testing: like it would turn a few times and then lock up, turn a couple of times and lock up again.

Anyway, I primed the carb with some gasoline because the vehicle has been stranded in the yard for I don't know how many months now (trying to pour a little gas into the two-barrel's carb vent at the same time). I turned the key, the starter cranked over, the motor started, it ran for a couple of seconds, then it died. I primed the carb a second time and then turned the key to re-start: nothing happened. The starter would not crank.

I left the key in the "on" position and checked for current at the coil. It seemed no current at the coil now.

I turned off the ignition key. I attached the remote starter switch and I ran a jumper wire from the positive battery terminal to the positive coil terminal. I primed the carb and the motor started and died a few times. Finally, it idled and ran all on its own, with the jumper wire still connected to the coil.

I shut the motor off after a couple of minutes and tried the key again. No, not working. I found I have a horn now, parking lights, brake lights, and head lights. Beginning to think we have a problem with the ignition switch itself.

IMG_0462.jpg
 
Dibbons,
I'm afraid you're going to burn something up testing like that.

It's much better to work systematicly from the power source back.
Lemme explain.
You can use either voltage or resistance when looking for a complete break in the power feed.
I checked for power to the tail/stop light fuse--checked out OK(current available there)
H'm doubt you measured current. Current is only flows through the fuse when one of those light are on.
Voltage should be present whenever the battery is connected, whether or not the light is on.

So what's this got to do with finding the fault?
Well, for one, it lets you use the car's ammeter as a trouble shooting tool.
Step on the brakes, or turn on the tail lights, and the ammeter will show how much current is flowing out of the battery.
No ammeter movement, no flow.

(Another thing is useful for is preventing a meltdown or fire. If you see the meter pegging, then that's 40 amps flowing through it and that will quickly cause damage. Don't wait for the fusible to melt or the battery to cook! )

Next is Systematic checks from the power source.
On a '65, if anything turns on, other than the horn, then the connections are good enough for some power to flow to the mainsplice.
The ammeter will also indicate how much current is flowing from the battery when that item is turned on.
Even though the starter gets power directly, the power for the starter relay and ignition flow through the key switch. So that current shows on the ammeter when the key is in start.

upload_2022-3-14_20-30-40.png


Now lets talk about using voltage measurements to narrow the down the fault.

Begin with establishing connection at the battery. Key off, doors shut.
1. Battery voltage
upload_2022-3-14_20-49-4.png


Then work your way down the line. So next junction is at the starter relay
upload_2022-3-14_20-51-14.png


Then if accessible - on a 1965 it is - at the firewall connector
upload_2022-3-14_20-53-19.png


At this juncture, the next step in line is to go check voltage to ground on the inside at the firewall, and then very carefully at the ammeter, fusebox 'hot' side, and the key switch feed.

However, it may make sense to jump ahead and see if there is battery voltage at the alternator's 'Batt" terminal.
upload_2022-3-14_20-58-21.png


If there is battery voltage at the alternator's batt terminal, then you know everything in between those two are connected.
So then you can go to the fusebox, key switch, and headlight if need be.

Remember, checking voltage with no current flowing doesn't reveal poor connections versus good connections. It just shows there is a connection.

To find a poor connection, use the same sequence, but with current flowing through the wires and connections of interest.
When you find a lower voltage, that indicates there was a poor connection in the current path between the battery and where you are measuring.

Now that the battery has been used for all this testing, please please please remember to recharge the battery on a charger before starting the engine.
 
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Mattax, is it necessary to have a fuse link on alternator output wire if there's one on red batt. wire at bulkhead? I could see where excess alt output could overheat wires before current exits firewall and hits that "batt" red wire fuse link at starter relay.....but please correct me if I'm wrong.
Nice diagrams, by the way. Thanks.
 
Mattax, is it necessary to have a fuse link on alternator output wire if there's one on red batt. wire at bulkhead? I could see where excess alt output could overheat wires before current exits firewall and hits that "batt" red wire fuse link at starter relay.....but please correct me if I'm wrong.
Nice diagrams, by the way. Thanks.
High current can overheat the wires and a fusible link is really no protection against typical high currents.
To melt a 16 gage wire quickly takes ALOT of current. I don't know the amount, but its got to be in excess of 100 amps.

The fusible link protects against battery positive shorting to ground. A battery can easily provide 100 or 200 amps (thats what's needed to spin the starter). It's just like uncontrolled arc welding if a wire (or your wedding band) accidently grounds any of the main wires. There's nothing to shutoff the spark show. So that's what fusible link does - it disconnects the battery.

Putting a fusible link in the alternator output is adding a restriction to the line.
In most cases when there is a short in the main, the alternator field won't get any current. Nor will the ignition. Either way the alternator is no longer capable of generating power. All of the electrons are taking the short cut and avoiding work.
 
The more complete set of diagrams:
Voltage is excited electrons, or potential energy.
Current is electrons moving.

Current flow with engine running and the battery recharged would look like this.
upload_2022-4-9_11-32-40-png-png.png

If we measured it, the system is roughly at 14 volts when the alternator is working properly.

Lets say the headlight wire insulation got damaged and the car hit a bump such the bare wire touched the metal dash.
That easy path to ground kills the ignition and field.
upload_2022-5-31_12-40-59-png.png

However as voltage drops below 13 Volts, the path is clear for the battery to take the same opportunity.
upload_2022-5-31_12-41-24-png.png


If there is a fusible link, that should stop the current flow before too much damage occurs.
upload_2022-4-10_20-22-47-png-png.png
 
So the alternator cannot overcharge, and send too much current to the main splice, possiblly burning ignition switch or anything else connected to the main splice? I bring this up because one of the diagrams shown in MAD does show a second fuse link in the alternator wire:
Catalog (madelectrical.com)
However, This diagram also has the mod where the alternator output will be routed directly to the BAT. POS. stud at the starter relay, rather than going thru the bulkhead to ammeter (which I bypassed back to the batt red wire). So maybe this mod necessitates a second fuselinK?
 
I put two maxifuses in my engine harness in the Barracuda. One is on the charge wire from the alternator to the battery. The other is on the main power feed to the interior. I found a two-fuse holder in a Mazda at a wrecking yard.
 
So the alternator cannot overcharge, and send too much current to the main splice, possiblly burning ignition switch or anything else connected to the main splice? I bring this up because one of the diagrams shown in MAD does show a second fuse link in the alternator wire:
Catalog (madelectrical.com)
However, This diagram also has the mod where the alternator output will be routed directly to the BAT. POS. stud at the starter relay, rather than going thru the bulkhead to ammeter (which I bypassed back to the batt red wire). So maybe this mod necessitates a second fuselinK?
MAD has to do it with their hack to protect the alternator output circuit from the battery. Short to ground at the alternator output stud or inside the alternator does happen occassionly.
One of the downsides to their idea is that all of the alternator output current must flow through that link. Then the portion needed to run the car and accessories must flow through another link. Its not an awful design, but its not brilliant. Chrysler did somehting similar in '76 A-bodies as did AMC Jeep in '86-91 Sjs.

Another downside to the mad design is that it makes a longer route to get to all of the equipment, except for the battery. Unless the car has been modified, battery charging should not be the alternator's main job. It supposed to be a sidejob that's only needed after starting, or occassionally after stop lights at night when the wipers and heater are running.
 
So, given the common ammeter bypass in which both ammeter wires are connected,
(alt wire not going to starter relay as per MAD), the alternator and output wire are protected from a. battery short with just the fuse link on batt. wire going to , formerly going to ammeter?
 
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