Fusible Link Burnt….why?

[westie47]

Today while my car was idling, the fusible link caught on fire and burnt up. I understand that it did it’s job, I’m just not sure why now???
I’ve had the car running for a few weeks now, just tuning and idling. Yesterday I took it on a short road test. No problems. When I tried to start the car after I got home, I found the battery was dead. Obviously the alternator wasn’t charging.
Everything on the car is new…battery, alternator, wiring harnesses, regulator, etc etc.
The only thing I did different today was move the green wire to the other prong on the alternator (circled in red). I’ve since move it back. Could this be why?
I really struggle with electrical and feel I am missing something simple. I got the 95 amp alternator.

 

[440 PHIXX]

If the fusible link burned up, something shorted out. You can think of it as a long “slow blow” fuse.

 

[PlymCrazy]

Is it possible that when you moved the green wire to the other terminal, that terminal was grounded? If so this would have full-fielded the alternator. That would potentially cause some burned up wires at the very least from the higher current coming out of the alternator.

Did you recently replace the alternator? Did they give the correct one?

 

[Jerry Hall]

Did the fusible link burn up after moving the green field lead or was it already burned up.

 

[kiwigtx]

If the fusible link burned up, something shorted out.

^^^^^^ This.

Find the short, then proceed.

 

[Geoff 2]

A dead battery could be alt not charging...or battery died from age or internal fault.
I would get a new/different battery. Get 60-100 amp cct breaker & wire it in temporarily in place of the FL. Start engine, check that the alt charges. If ok, probably the battery. If the cct breaker trips, it becomes a process of elimination to find what is causing the short cct. Start with the alt by swapping it.

 

[MoparLeo]

Off the subject, What are you using for the kickdown linkage on the trans and is the steering coupler just not quite finished restoring or is it coming apart ?

 

[Gold Rush]

Today while my car was idling, the fusible link caught on fire and burnt up. I understand that it did it’s job, I’m just not sure why now???
I’ve had the car running for a few weeks now, just tuning and idling. Yesterday I took it on a short road test. No problems. When I tried to start the car after I got home, I found the battery was dead. Obviously the alternator wasn’t charging.
Everything on the car is new…battery, alternator, wiring harnesses, regulator, etc etc.
The only thing I did different today was move the green wire to the other prong on the alternator (circled in red). I’ve since move it back. Could this be why?
I really struggle with electrical and feel I am missing something simple. I got the 95 amp alternator.

View attachment 1345043

View attachment 1345044

View attachment 1345045

I see in the 1st photo this alternator had two field terminals. The alternator is not a square back but is also not the old style round back which is a bit confusing. Is this alternator manufactured to be used on a modern dual field terminal system or is one of those actually grounded to the alternator case? Before you continue on this journey that needs to be determined.

Totally disconnect all wires from the alternator then use a multi meter to test continuity between the two field terminals and the alternator case. If one of them shows no resistance to the alternator case and the other terminal shows some resistance then you would connect the green wire to the terminal with some resistance and nothing to the other terminal. If neither terminal shows no resistance check from terminal to terminal. You should see some resistance if the alternator you have is manufactured for use in dual field wire modern MOPAR systems.

Hope that gets you pointed down the correct path.

 

[westie47]

Is it possible that when you moved the green wire to the other terminal, that terminal was grounded? If so this would have full-fielded the alternator. That would potentially cause some burned up wires at the very least from the higher current coming out of the alternator.

Did you recently replace the alternator? Did they give the correct one?

It’s a new PowerMaster alternator from Summit.

 

[westie47]

Did the fusible link burn up after moving the green field lead or was it already burned up.

It burned after I moved the field lead.

 

[westie47]

Off the subject, What are you using for the kickdown linkage on the trans and is the steering coupler just not quite finished restoring or is it coming apart ?

The steering coupler is coming apart, I can’t seem to get it to stay on.
I just pulled the factory kickdown linkage out because it wasn’t working with the aftermarket intake so I ordered a Lokar kit.

 

[westie47]

I see in the 1st photo this alternator had two field terminals. The alternator is not a square back but is also not the old style round back which is a bit confusing. Is this alternator manufactured to be used on a modern dual field terminal system or is one of those actually grounded to the alternator case? Before you continue on this journey that needs to be determined.

Totally disconnect all wires from the alternator then use a multi meter to test continuity between the two field terminals and the alternator case. If one of them shows no resistance to the alternator case and the other terminal shows some resistance then you would connect the green wire to the terminal with some resistance and nothing to the other terminal. If neither terminal shows no resistance check from terminal to terminal. You should see some resistance if the alternator you have is manufactured for use in dual field wire modern MOPAR systems.

Hope that gets you pointed down the correct path.

Thanks! I’ll try that.

 

[Dave6T4]

What year car are you working on? Do you have the early style small square voltage regulator? The originals of these were mechanical points type, but did not work well with electronic ignition conversion. Later versions were electronic with a circuit board to work with electronic ignition. If this is the style of regular you have, one of the field terminals should be grounded. I always ground the one you have circled. This would be the reason your alternator was not charging the battery.
95 Amp. PowerMaster alternator; did you upgrade your charging circuit to 8 Ga. wire as instructions tell you to do? If you did not, this is the electrical equivalent of pushing a golf ball through a garden hose. I put the same alternator on my '64 Polara, and did the wire upgrade. There are threads on here about this. Burnt fusible link is usually a short circuit, but could be that golf ball thing.

 

[Jerry Hall]

It burned after I moved the field lead.

Then it stands to reason that's what burned the fusible link. You connected the field wire directly to ground causing a short.

 

[Mopars & Missiles]

Then it stands to reason that's what burned the fusible link. You connected the field wire directly to ground causing a short.

And most likely damaged/destroyed the Voltage Regulator in the process.

 

[Dave6T4]

This is a double field round back alternator, and in the correct year application ('69-'70 ?), would have a wire that also plugs to this circled terminal. People have also been able to use this alternator in single field applications, by grounding the circled terminal to the case with a small wire. The proper single field alternator is a similar round back item with the circled field grounded internally by the manufacturer. On this style alternator, there is no prong onto which to plug a second wire. The single field system uses the small squarish voltage regulator. Both the dual field round back and later square back alternators use the later flat electronic voltage regulator. If the second field is not grounded when used on a single field application, the alternator will not charge the battery.

 

[PlymCrazy]

'69 and older used the roundback casing, has a single-field terminal, paired with the points type 2-wire VR. '70 and newer used the squareback casing, has dual-field terminals, paired with the 3-wire electronic VR.

However lately a lot of rebuilt alternators are no longer staying year-range specific with the casing so you'll see what appears to be a mismatch often when purchasing. They differentiate by how they install the field terminal(s) in relation to ground.

It's critical on the 2-wire VR that one terminal on the alternator is grounded and the other is open(often times you see today that the grounded terminal is clipped so it can't be used). The open field terminal is what you'd connect your green wire to, not the grounded one. Test to be sure.

On the 3-wire VR both the blue and green wires are attached to the alternator's (2) field terminals, both of which are open. Test to be sure.

My advice is regardless of what the alternator looks like(roundback or squareback) be sure to test it with a multimeter before installing and especially before starting the engine.

Check your current VR to assure it's not damaged and replace if so. Then be sure you have the correct alternator to match. Do this by testing it with the multimeter at the field terminals(s) in relation to ground(I personally use the case of the alternator as a ground reference myself).

Edit: At least through '70 or '71 had the roundback case still...not '69 as previously stated...

 

[Jerry Hall]

'69 and older used the roundback casing, has a single-field terminal, paired with the points type 2-wire VR. '70 and newer used the squareback casing, has dual-field terminals, paired with the 3-wire electronic VR

1970 was a round back alternator with dual fields, not a square back alternator. I'm not exactly sure when the square back appeared, but I'm sure about 70. 1969 and back were as you stated single field round back alternators.

 

[PlymCrazy]

1970 was a round back alternator with dual fields, not a square back alternator. I'm not exactly sure when the square back appeared, but I'm sure about 70. 1969 and back were as you stated single field round back alternators.

Yeah, good catch. My mistake on that. I think it was actually '71 or '72 the squareback was introduced? Ever repeat the same advice over and over and forget the original details? Guilty of it here LOL.

Even more reason to test that alternator to assure you know how it's wired. Eliminate all the potential for confusion by the various case styles as they mix them up a lot on the rebuilds today. I recall hearing recently that they are running low on roundback cases, hence so much confusion surrounding this.

 

[Nacho-RT74]

Squarebacks on 72, but 70/71s still being roundbacks were already dual field.

Latelly the problem with them is maybe 60% of the rebuild services, dealers and even some aftermarket brands etc... offers dual field setups converted into single fields grounding one of the fields BUT with no instructions about that and keeping the grounded brush prong in place instead clip it off to save from conect the green wire from single field setup into that grounded brush, causing a short. On dual fields the green wire "is negative"(*) while on single fields is positive. So if you connect a green wire from a single field system into an alt with a grounded brush straight to that one, will burn as soon you put the key in RUN.

(*) Yeah right... the green wire on dual field is the "return line" to the regulator, which will switch on/off to ground to regulate the current running throught the rotor... but is the same than a bulb... and the same than a single field where one of the brushes is GROUNDED. The fact is you need both poles to make to work anything, so in therms of practical facts one side is positive and the other side is negative.


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