Fusible Link Burnt….why?

[MoparLeo]

Mopar A B E Body 66-73 3" Steering Coupler Retainer Clamp STAINLESS DMT 2996935 | eBay

 

[westie47]

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.

It's a 69 Coronet with 440. I will check the voltage regulator, I'm not sure which model I have.

 

[westie47]

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

How do you test the voltage regulator?

 

[kiwigtx]

To answer the title of this thread about as plainly and blunt as can be.....

You failed to read the FSM - the part where it says to disconnect the battery before doing any electrical work.

The Fusible Link did its job by the sounds of things. Be happy that it worked.

 

[westie47]

To answer the title of this thread about as plainly and blunt as can be.....

You failed to read the FSM - the part where it says to disconnect the battery before doing any electrical work.

The Fusible Link did its job by the sounds of things. Be happy that it worked.

Soooo, I should’ve disconnected the battery to start the car? Thanks for the sound advice.

 

[Sparky Anderson]

Even though new it may be a faulty Alternator and could have the insulated washer missing, a picture from rock auto may give you the idea. It's been really bad with aftermarket parts, check your replacement parts with a fine tooth comb!

 

[westie47]

Even though new it may be a faulty Alternator and could have the insulated washer missing, a picture from rock auto may give you the idea. It's been really bad with aftermarket parts, check your replacement parts with a fine tooth comb!
View attachment 1346606

Which insulated washer are you referring to?

 

[Nacho-RT74]

Which insulated washer are you referring to?

the one down the brush retaining screw, to keep the prong in place ( and insulated ) againts the brush holder. This washer is tipically replaced by a metallic one by dealers to offer a "single field" alt setup out of a "dual field" alt setup. This washer replacement becomes one of the insulated brushes into a grounded one.

 

[westie47]

the one down the brush retaining screw, to keep the prong in place ( and insulated ) againts the brush holder. This washer is tipically replaced by a metallic one by dealers to offer a "single field" alt setup out of a "dual field" alt setup. This washer replacement becomes one of the insulated brushes into a grounded one.

I checked, mine has both insulated washers.

 

[westie47]

So, I ordered a new fusible link from Classic, moved the field wire back to the original field it was on when it was running fine. As soon as I connected the positive battery terminal, the new fusible link immediately burnt. Now I'm confused.....

 

[Sparky Anderson]

Which insulated washer are you referring to?

The black plastic washer in the diagram, do u have a ohm meter to test to make sure it's not grounded, or showing resistance, should be infinite. Check that to rule it out in troubleshooting,

 

[Nacho-RT74]

If the fuse link is burning as soon you connect the batt before set the ign switch on RUN, is not brush related, since those are energized with Ign switch. Is related with alt-amm-starter relay-batt wiring. Nothing else

 

[RemCharger]

the one down the brush retaining screw, to keep the prong in place ( and insulated ) againts the brush holder. This washer is tipically replaced by a metallic one by dealers to offer a "single field" alt setup out of a "dual field" alt setup. This washer replacement becomes one of the insulated brushes into a grounded one.

Good information.
I guess those that disagree have never come across this yet.

 

[Nacho-RT74]

yeap... the problem is the brush they ground still gets the prong there, so without any information from dealer this could become on a HUGE problem as soon you put the key in RUN causing a short able to melt the wire between reg and brush and even the ign wire between reg and ign switch if you conect the field wire from single field setup on that brush. Dealers should cap off, clip off or bent the grounded prong to don't allow the conection on it. A basic shrinking tube on prong should be enough to save from that mistake and would still keep live the brush if you want to become back your alt onto a dual field like originally is/was without a brush replacement, just getting the insulation washer installed back. Just in case you want to upgrade to dual field/electronic regulator system later.

There are couple of threads around about this washer and with pics on board.

 

[bobsgtx]

FYI on electrical shorts(grounds) I usually put a 10 or 15 amp auto reset circuit breaker in place of fuse or your case fusible link. I would get the metal can one with two studs. Since your problems started at the alternator I would start by disconnecting all the wires and testing them with an ohmmeter. With alternator wires disconnected put the circuit breaker in place of the fusible link and hook the battery up and see or hear if the circuit breaker trips. This will tell you if you have an alternator problem or not.

 

[westie47]

UPDATE!

I had the alternator and voltage regulator tested by a local guy who specializes in them. The alternator and VR we’re fine. He then set my alternator up for single field and bench tested it. It didn’t quite live up to the 95 amp rating by PowerMaster lol He got to 90 amps with the voltage turned up to 16V!
He also showed me what probably caused the short circuit in the first place. (See pic) The circled piece was touching the case. He also gave me some of the correct connectors for the bulkhead connector. I bought a 14g fusible link from the local auto parts store and installed it.

When I connect the battery I have 12.54V at the battery, at the starter, at the starter relay and at the bulkhead connector (fusible link). I don’t have anything at the alternator or VR. I also have nothing at the ignition switch.

Any ideas where to start under the dash? Obviously the fusible link burning caused something under the dash.

 

[Nacho-RT74]

I already mentioned... check the full line. I point out to the amm studs, or ammeter itself... amm isolation with cluster which ocasionally could short to ground depending on the amm conditions... or related wires. ALSO IGN SWITCH AND HARNESS.

The fuse link actually protects this main circuit ( charging, ign switch ) AND the RUN circuit to the engine bay. Most of the rest of the car after this is protected by individual fuses on fuse box or breakers which will blow out way before the fuse link in localized short.

 

[Gold Rush]

What Nacho said got me thinking.... Did anyone ask if you have a factory service manual for your car?

I've been professionally and otherwise chasing sparks for well over 50 years and have found that doing so without proper technical data is very often a very confusing exercise. After I bought my 1st Charger back in 1974, the first thing I bought was the manual for the car. Back then the car was new and rarely needed fixing. Now that I have been restoring my second '74 SE Brougham, that manual has become extremely useful.

 

[RJRENTON]

UPDATE!

I had the alternator and voltage regulator tested by a local guy who specializes in them. The alternator and VR we’re fine. He then set my alternator up for single field and bench tested it. It didn’t quite live up to the 95 amp rating by PowerMaster lol He got to 90 amps with the voltage turned up to 16V!
He also showed me what probably caused the short circuit in the first place. (See pic) The circled piece was touching the case. He also gave me some of the correct connectors for the bulkhead connector. I bought a 14g fusible link from the local auto parts store and installed it.

When I connect the battery I have 12.54V at the battery, at the starter, at the starter relay and at the bulkhead connector (fusible link). I don’t have anything at the alternator or VR. I also have nothing at the ignition switch.

Any ideas where to start under the dash? Obviously the fusible link burning caused something under the dash.

View attachment 1350242

The component part circled is the positive diode assembly (the negative diodes are pressed in the case) and MUST BE INSULATED FROM THE CASE IN ALL REGARDS. THERE IS A THIN MICA INSULATING WASHER/SPACER BETWEEN THE DIODE ASSEMBLY, THE OUTPUT STUD/CAPACITOR STUD AND THE CASE. If the conbection is compromised, a direct short circuit connection will exist......use caution when attaching the output wire to the alternator output stud to prevent a short circuit........just thought you might like to know.....
BOB RENTON

 

[Nacho-RT74]

yeap, on both alts, either round backs or square backs, the positive diodes bank must be propperly insulated everywhere. Inside it gets as mentioned a mica insulation AND a nylon bushing around the stud into the case. if either of one fails, you can get a short as soon you conect the batt. As mentioned, the rest of the circuits are fused or breaker protected BUT the main charging circuit and ign switch which are just protected by the fuse link.

After the ign switch just the ACC circuit once arrives the fuse box but just after the fuse box for each one of the circuits, not between Ign switch and fuse box.

Same about the cab batt circuit coming out from the main charging wiring splice.

Run circuit is just protected on SOME models for the interior network such as cluster and some other devices ( seatbelt warning system ) but not on engine bay. However this network won't be energized untill you activate the ign switch.

Same about Ign2 and Start circuits.


In any case, if you don't activate the ign switch, just the red line arriving to will be energized from the charging network... like the batt source on fuse box
I made this diagram LOOONG time ago and has been copied allmost everywhere.

This is the main charging network allmost for every mopar ( bulkhead disposition made for E and 71/74 B body. These will be the constant hot lines protected ONLY by the fuse link

Of course, starter relay and motor are also out of the fuse link protection and they in fact don't have any protection, so those can be discarded on the checking out process being the fuse link is the one blowning out.