14 GA or 16 GA Fusible Link?

[dibbons]

We have a 1965 Plymouth Valiant Signet Convertible with no accessories (manual steering, manual brakes, no A/C, no radio) just has a heater, horn, and 6014 headlamps (factory were 6012). However, evidently a previous owner installed a radio which is now missing (but there are dual radio antennas installed on the two rear quarter panels.

I have my doubts whether or not the firewall fusible link (bottom in photo) has been replaced with a fusible link or a straight wire so I plan on replacing it now. I have found two fusible links in my stash of electrical parts: one is labeled 14 gauge (center in photo) and the other labeled 16 gauge (top in photo). Which one was factory installed and which one is recommended by my brother Mopar forum members? Thank you.

 

[66Valiant528]

Check the wiring diagram to see how fat the alternator output wire is. Then the link is 2 sizes smaller. So if it's 10 gauge then it's 14 fuse.

 

[dibbons]

According to page 8-109 of the Plymouth 1965 Service Technical Manual the hot wire from the alternator to the bulk head connector is labeled R6, is black, and is 12 gauge.

However, I recently installed a new under-hood wiring harness I purchased online and it's hard to tell what gauge wire was used in that spot (the wire is black anyway). The other factor is: I am sure the installed alternator is not the factory installed alternator and may now have an amp output greater than the original factory rating. So now it's going back to a kind of guessing game.

 

[Mattax]

According to page 8-109 of the Plymouth 1965 Service Technical Manual the hot wire from the alternator to the bulk head connector is labeled R6, is black, and is 12 gauge.

However, I recently installed a new under-hood wiring harness I purchased online and it's hard to tell what gauge wire was used in that spot (the wire is black anyway). The other factor is: I am sure the installed alternator is not the factory installed alternator and may now have an amp output greater than the original factory rating. So now it's going back to a kind of guessing game.

View attachment 1715905140

As far the '65 fusible link, it doesn't matter that much what the alternator 'rating' is.
The main job of the fusible link is to protect the wires.
Chrysler used a 16 gage fusible link to protect the 12 gage wires.
It's placed in the battery line so as to protect stuff from battery grounding.
There's no link in the alternator output or hot wire as you call it.

 

[Mattax]

Electrical Accessories & Service (Session 207) from the Master Technician's Service Conference

Isn't this your picture form one of your cars?

and one from someone else, also supposed to be a '65

 

[Mattax]

It's placed in the battery line so as to protect stuff from battery grounding.

Lets say the headlight wire insulation got damaged and the car hit a bump such the bare wire touched the metal dash.

Now that's the easiest path to ground. So instead of power going from the alternator to the ignition, it diverts to ground.

That kills the ignition and field.
However as voltage drops below 13 Volts, the path is clear for the battery to take the same opportunity.

The 16 gage wire in the link should melt before the 12 gage wires, and hopefully before the connections get too fried.
That should end the spark show under the dash fairly quickly and before stuff under there catches fire.

That's the concept. So even if there is a 10 ga wire from the alternator to the mainsplice, no reason to go larger on the fusible link.

Some cars have multiple fusible links and those designs have different needs.

 

[dibbons]

That photo in #5 is from my other '65, the Formula S.

 

[dibbons]

And just for some added information, in the back of the Plymouth 1965 Technical Service manual there is a section of the book called "Specifications" and on page 12 of that section the alternator ratings are: six cylinder in AV-1 models: 26 amperes, all other V-8 models: 34.5 amperes, and heavy duty/A-C: 39 amperes. Pretty conservative compared to current vehicles.

Currently Rock Auto only shows listings for 55 and 60 amp alternators for a '65 Valiant.

 

[Mattax]

A few of us have brought this up in various threads.
What ever Chrysler used for a rating system was their own. Same for the aftermarket. No real industry standard.
One solid performance measurement we have is the output test in the FSM. You'll find those are almost always done at 1250 rpm, 15 Volts.

As I mentioned in Rusty's thread, it seems that the aftermarket rebuilders are replacing the rotors with a higher draw unit.
These rotors may be capable of producing 60 amps when matched with the appropriate stator. BUT that's not doing us any favors because the field current draw is twice as high as the proper unit. Not only is that bad for the wiring and wasting power, its creating more heat in the alternator.
All I can say at this point is the same thing I said to Rusty. Measure the rotor reistiance if you have it open, and when installing check the field current draw. Its not a difficult test.

 

[Mattax]

cutting and pasting the checks.
from the '73 FSM. Slip ring to slip ring the rotor should be 3 to 4 ohms at room temperature. [/QUOTE]

Field draw test.
First make sure there isn't a short to ground. ( Measure the resistance from brush field terminal to ground. Measured through the brushes may be more than 3-4 ohms, or if one of these '60 amp' rotors maybe as low as 2 ohms. )
Then loosen the alternator enough you can turn the pulley by hand.
Using a meter that can measure a few amps, set it to the 10 amps scale and alligator clip it like this.
Be super careful not to let either clip touch ground.

[/QUOTE]

Its in the service manual but hopefully this makes it clearer.

 

[66jim]

Put a amp meter where the link is an measure the max draw, then replace the link with an inline fuse and of corse keep a spare in the glovebox.

 

[AJ/FormS]

Put a amp meter where the link is an measure the max draw, then replace the link with an inline fuse and of corse keep a spare in the glovebox.

While that works;
Is that gonna get you home on a dark and stormy night?
Fusible links are NOT like fuses. It usually takes quite a while for an F-link to sacrifice themselves; small overloads could go un-noticed for years; while a blown fuse could lead to multiple replacements, eventually leading to the installation of a fuse much too big, offering no protection at all.

 

[66jim]

While that works;
Is that gonna get you home on a dark and stormy night?
Fusible links are NOT like fuses. It usually takes quite a while for an F-link to sacrifice themselves; small overloads could go un-noticed for years; while a blown fuse could lead to multiple replacements, eventually leading to the installation of a fuse much too big, offering no protection at all.

Uh, no. Is that why fuseable links links are used in your home or industry and anywhere else. There are slow blow fuses for momentary spikes and surges. A blown fuse indicates a problem how you deal with the problem is up to you. Fuseable link is nothing more than link of smaller gauge sized to fuse first, nothing more.

 

[AJ/FormS]

You can do whatever you like.
As for me, I am NOT subbing in a fuse in the place of a Fusible-Link .
Nor would I ever recommend anyone else do it......

 

[dibbons]

I installed the new 16 gauge fusible link and the '65 Valiant is up and running again. I found a common "fault" when checking charging voltage which is I need to rev above idle speed before the alternator begins to show a charge. I found that same anomaly in my '72 Satellite.

The initial problem with the Valiant is that while idling one day it just stopped running and every single electrical component in the vehicle went dead at the same time.

 

[Mattax]

I installed the new 16 gauge fusible link and the '65 Valiant is up and running again. I found a common "fault" when checking charging voltage which is I need to rev above idle speed before the alternator begins to show a charge. I found that same anomaly in my '72 Satellite.

The initial problem with the Valiant is that while idling one day it just stopped running and every single electrical component in the vehicle went dead at the same time.

Are you checking voltage or just looking at whether battery is charging?
Using both will help track down the cause.
When checking voltage, I usually begin with the battery. Then depending on what I find compare with alternator and then regulator feed.

 

[67Dart273]

All this discussion boils down to this, in my opinion:

What "Chrysler did" was NOT good engineering. There needed to be a MUCH greater "ratio" between the size of the charge wiring (larger) and the fuse /fuse link (smaller.) And of course the marginal design of the ammeter and bulkhead connector.

MA KNEW THIS to some extent as evidenced by two things:
1.....The "police/ fleet/ taxi" wiring used with 65A alternators which was effectively a partial bulkhead connector bypass, using larger wire
2.....The fact that "Ma" experimented with external shunt ammeters on some models, starting with when? 70? 72? Fury and others. ---and finally going with external shunt in A bodies in 76

I disagree with Mattox about using fuses. Proper fusing is fine, but you are still fighting the
A....need for high current capacity because of the alternator output vs:
B....the small size of the wire, so regardless of fuse or link, you cannot practically "protect" something that is already undersize, while still keeping "the system" online!!!

There is no easy answer. If you want "more alternator" then increase the wire size, do a bypass, or parallel another wire with existing. There are several methods to deal with the ammeter depending on "wants" or skill
I LIKE ammeters, but for my own car I ended up doing a voltmeter conversion.

IF I LIVE long enough to get the 74 Scamp going again (fighting water leaks) I intend to experiment with a 76 style external shunt ammeter, and see how easily that can be made for "retrofit"

 

[67Dart273]

"The trouble" with external shunt ammeters generally and practically:

I've had some Ford Rangers, and friends with Chev and Ford pickups. ALL had external shunt ammeters, and ALL had the same problem:

They were "numb." That is, you could get in, turn on the headlights, and you had to stare intently at the ammeter to see if it even moved!!! Almost useless for smaller amperages. I actually added some wire to one Ford harness to "de-numb" the ammeter. All these, whether Chrysler, Ford, or GM, used part of the harness as "the shunt." This means they can never be very accurate, or repeatably "accurate." They are, in fact, a huge compromise

And that is likely, exactly, why most (all?) modern vehicle manufacturers went to VOLTMETERS They themselves are a problem, as the faces are simply not accurately or meaningfully calibrated in many cases.

 

[dibbons]

I honked the horn with the motor off and the ammeter did not budge. It shows a charge with engine running.

What is good on the '65 design, is that the ammeter wires don't use the main harness plug coming from the engine compartment, they have their own unique metal clamps with screws where they pass through the firewall all on their own.

 

[Mattax]

I honked the horn with the motor off and the ammeter did not budge. It shows a charge with engine running.

What is good on the '65 design, is that the ammeter wires don't use the main harness plug coming from the engine compartment, they have their own unique metal clamps with screws where they pass through the firewall all on their own.

That's correct for '65.