Bulkhead wiring/fusible link questions

[NukeBass]

I have a 73 Duster and, hopefully, within the next month will be bypassing the bulkhead connector. I have the 73 manual with the wiring diagrams and this diagram shows a 60A alternator option that bypasses the bulkhead so I am planning on copying this for the most part. This leads me to a few questions...

1. Fusible link size: I am planning on using 8 gauge wire as shown on the wiring diagram. The places I have looked say to use a fusible link 2 sizes smaller than the wire size used which puts me at a 12 gauge fusible link. The wiring diagram shows Plymouth used a 16 gauge fusible link for both the 60 amp alternator and normal alternator wiring, so I'm not sure if I should use a 12, 14 or 16. 14 and 16 are readily available at the local parts stores, but I think I'll have to order a 12.

2. Fusible link connection method: I was thinking it would be nice to have an easily removable connector so I've thought about splicing in a bullet or similar connector in case I have to replace the fusible link down the road. On the other hand, neither version of the car (original slant six or current 340) have ever melted the fusible link (the car has been in the family since 73) so should I even worry about trying to get a removable connector or just splice it directly to the wire?

3. Bulkhead wiring: The wiring diagram indicates that the bypass wires from the alternator and the battery are connected (with fusible link at the starter relay) directly to the ammeter and the "stock" wires removed (or at least I think that's what it is telling me) from the bulkhead. This seems simple enough and the main power splice on the alternator side inside the car would be fed from the connection at the ammeter. What I'm not sure about is that my bulkhead points P and Q are connected at the motor harness and the diagram doesn't say anything about changing that wiring. P is the 12 gauge black wire alternator wire (and the most corroded looking connection) and Q is the 14 gauge brown wire that connects to the ignition coil and the ballast resistor in the engine bay and (converts to 12 gauge) the start position on the ignition switch inside the car. What does this parallel connection do? Is there a way to bypass it or is it just easier to fix the connector in the bulkhead and leave the stock alternator wiring alone?

I've been putting this bypass off for a while and hope to get it done in the near future. I have less than 11V in the car when anything is turned on (run position, headlights, whatever)

Thanks!

 

[Mattax]

Not sure what you're trying to accomplish, But here's the fusible links are there to protect the charging circuit and everything withut a fuse from the battery shorting. Explained better here:
Fusible Links in Charging Systems with Ammeter

If you want to rewire the charge circuit without an ammeter, and distribute power from the battery, then you must fusible link each circuit coming off the battery. Thats when the 2 gages smaller rule of thumb comes in. Base it off of the smallest wire in the circuit being protected.

If you just want to get a better connection in the alternator and battery feeds, then take them through the firewall with a grommet with new wires. You can leave the old ones and run in parallel, or remove the old ones. If running in parallel, probably better to use one fusible link, but its up to you.

Bulkhead connector bypassed.

Same but original wires retained (operating in parallel). See post 6 of original thread on Charger forum.

P is the 12 gauge black wire alternator wire (and the most corroded looking connection)

Alternator output wire connects to the main distribution (welded splice) inside the car. If there is corrosion or other damage to the connections, this is where the voltage is being lost when the engine is running and equipment is on.

Q is the 14 gauge brown wire that connects to the ignition coil and the ballast resistor in the engine bay and (converts to 12 gauge) the start position on the ignition switch inside the car. What does this parallel connection do?

Not sure what you mean by parallel connection, perhaps you are you refering to the field power on the alternator?
Turning the switch to start sends full voltage to the coil positive.
Releasing the switch to run sends full voltage to the other side of the ballast resistor, so the coil gets less the full voltage and current. The run wire also connects to the field of the alternator and the voltage regulator. The regulator 'reads' the voltage available and regulates by allowing the field to complete the circuit to ground (green wire)

Basic circuit. ( Wire for powering coil when starting is not shown, but attaches to the coil side of the ballast resistor. '73 colors may be different.)

I've been putting this bypass off for a while and hope to get it done in the near future. I have less than 11V in the car when anything is turned on (run position, headlights, whatever)

Running or on battery alone? Measured where? Look for the voltage drop from the battery (or alternator) if you want to find the locations of high resistance.

 

[NukeBass]

My plan is to run 8 gauge wire through the firewall into the ammeter as is outlined in the wiring diagram. There is a jumper at the bulkhead connection between ports P and Q. The wiring diagram in the service manual has various notes about with 60 Amp alternator and without 60 Amp alternator, but nothing with about this jumper. If I disconnect the original alternator wiring at the bulkhead, I don't know what will happen with port Q. However, I did just make a practice Packard 56 connection on some wire I have, so I think I'll just replace that alternator connection at the bulkhead and leave it wired as is so that I don't have to worry about the jumper wire.

The car has 12 V when just sitting (nothing on), but as soon as I turn on the headlights or move the key to any position (Run, Accessory) the voltage drops below 11V pretty much everywhere I take it (battery, ballast, alternator field wire, wiper motor), so I'm hoping bypassing/repairing the connections helps with the voltage drop.

Now all that's left is figuring how to connect the 8 gauge wire to the smaller fusible link wire.

Thanks!

 

[Mattax]

Could be a connection to insure a good feed to the field.
Putting your new wires in parallel and leaving the oriignals will work the same as now (but with less resistance).

My guess is the voltage in run yis from the current going to the field windings in the alternator, and a little to the ignition. If its 11 at the battery, there's no drop due to resistance downstream. Here's what I meant by drop. For example, if its 12 at the battery, 12 at the relay as 11 at the bulkhead, then there's resisantance between the relay and the bulkhead.

 

[GMachineDartGT]

I have a 73 Duster and, hopefully, within the next month will be bypassing the bulkhead connector. I have the 73 manual with the wiring diagrams and this diagram shows a 60A alternator option that bypasses the bulkhead so I am planning on copying this for the most part. This leads me to a few questions...

1. Fusible link size: I am planning on using 8 gauge wire as shown on the wiring diagram. The places I have looked say to use a fusible link 2 sizes smaller than the wire size used which puts me at a 12 gauge fusible link. The wiring diagram shows Plymouth used a 16 gauge fusible link for both the 60 amp alternator and normal alternator wiring, so I'm not sure if I should use a 12, 14 or 16. 14 and 16 are readily available at the local parts stores, but I think I'll have to order a 12.

2. Fusible link connection method: I was thinking it would be nice to have an easily removable connector so I've thought about splicing in a bullet or similar connector in case I have to replace the fusible link down the road. On the other hand, neither version of the car (original slant six or current 340) have ever melted the fusible link (the car has been in the family since 73) so should I even worry about trying to get a removable connector or just splice it directly to the wire?

3. Bulkhead wiring: The wiring diagram indicates that the bypass wires from the alternator and the battery are connected (with fusible link at the starter relay) directly to the ammeter and the "stock" wires removed (or at least I think that's what it is telling me) from the bulkhead. This seems simple enough and the main power splice on the alternator side inside the car would be fed from the connection at the ammeter. What I'm not sure about is that my bulkhead points P and Q are connected at the motor harness and the diagram doesn't say anything about changing that wiring. P is the 12 gauge black wire alternator wire (and the most corroded looking connection) and Q is the 14 gauge brown wire that connects to the ignition coil and the ballast resistor in the engine bay and (converts to 12 gauge) the start position on the ignition switch inside the car. What does this parallel connection do? Is there a way to bypass it or is it just easier to fix the connector in the bulkhead and leave the stock alternator wiring alone?

I've been putting this bypass off for a while and hope to get it done in the near future. I have less than 11V in the car when anything is turned on (run position, headlights, whatever)

Thanks!

Add a 10ga charge wire from the alt to the starter relay. This will greatly reduce the current going to the ammeter. All the failed bulkhead connectors I've seen are because of too high current along with oxidized connections.

 

[Mattax]

That's only OK if the wiring to the distribution point is improved (or the distribution reworked). Otherwise, all it removes is the loads from recharging or running on batteries. Power for everything else will still have to get to the main junction through the firewall. Since the main power wire (black from alternator to P) is in poor condition, with enough resistance, some power will look for a lower resistance route. That will be alternator to starter relay, to fusible link, to bulkhead, to ammeter to main junction.

The most important IMO for this car is to fix, replace or parallel the alternator output wire to main junction. Next would be the same for battery wires and connections to main junction. The most common failures I've personally seen with a-bodies have been in the headlight circuit. A relay arrangement solves that (if when keeping the ammeter, it draws from the alternator output).