What Gauge Wire

[Cudajason]

Years ago, I rebuilt the engine wiring harness in my cuda and added the amp gage bypass.

For some reason I used mainly 12 gauge wire and soldered the new wire into the smaller 16 gauge? wires from the original VR and Electronic control unit plugs.

I am struggling to remember why I jumped the size of the wire so much.

Now I have to replace the plug to the VR, should I re do everything with the the proper gauge wire (i.e., is the larger gauge wire into the smaller wire a potential issue)  or should I just cut off the old VR plug and solder in the new one.

Thanks,


Jason

[gzig5]

I use the heaviest wire I can for low voltage (12-24 VDC) circuits.  It is very surprising how much voltage drop there is through the wire when you start pulling serious amperage.  The lights on our cars are a good example and the relay wiring kits help a lot by going to better wire and feeding from closer to the source.  We had a new product development at work that uses several 24VDC fans to cool the power stage.  Turns out the fans pulled so much current that the voltage drop through 30' of 16ga wire was over 4VDC.  That was enough of a drop to cause the logic power supply for the control circuits to essentially brown out and the processor would reset at the strangest times.  The wire was getting HOT too.   Since then I've been pretty cautious with the 12v wiring in the car because all the connections and small wire add up to extra resistance.

[moparroy]

I would use nothing less than a 10 gauge wire for charging current. When I prepped my ammeter bypass wire I used some 7 gauge wire I happened to have.
As for the connections I put a completely separate single pin connection for the charging current wire, at each point where the harnesses connect - one at the engine connector and one at the bulkhead. The current capacity of the connectors worried me a bit as I used the original type pins but they seem to say they are ok for that. You need to use a suitable fusible link for whatever size wire you chose.
As for connecting #12 to #16 - well I would not do it - the #16 will become resistance and voltage drop point and potentially a heating point. Once a heating point starts it can lead to oxidation on the connector pins which will further increase the resistance and increase the local heat and it just snowballs from there. This is what IMO happened in a lot of Mopar bulkhead connectors due to the charging current - mine was well toasted.

[tparker]

I would use original wire size and not go smaller. Smaller wire causes more resistance and can heat up. In most cases it probably isn't a problem, but why risk it. Any thing carrying any good amount of current should obviously be thicker wire. Not sure there is any real benefit of thinner wire other than shoving it through a smaller hole. LOL

[Filthy Filbert]

If it's carrying current—alternator charge wire, headlights, etc.  don't skimp. Go big.   If it's just a sensor like temperature or oil pressure, then you can get away with thinner.

[dodj]

Turns out the fans pulled so much current that the voltage drop through 30' of 16ga wire was over 4VDC.  That was enough of a drop to cause the logic power supply for the control circuits to essentially brown out and the processor would reset

@gzig5
That would have driven me NUTS!
Probably would have had me getting a new board flown in after using the 'on hand' spare figuring the 'on hand' spare was bad as well. Bet more than one rep phoned in with help on that one.
@Cuda jason Other than physical limitation problems, going big will never hurt. Staying the same MAY hurt but going smaller will hurt.
FYI. I built my own harness as well. Bought all the connection hardware from local Chrysler dealer when they were still available. Changed all 16ga wire to 14ga. I used #8 motor lead wire for my alt bypass.

[Cudajason]

Thanks for the comments guys.

Here is my dilemma, The VR plug i purchased has 18 maybe 16 gauge wire. I used 12 gauge wire when I rebuilt the harness. Do I connect the 18 to the 12?  Do I rebuild that section at least with 18 gauge wire?  Do I try to find the barrel connectors that will work with the VR plug and upgrade to 12 gauge wire.

[Filthy Filbert]

the voltage regulator doesn't carry any serious current.  It's job is to sense the system voltage, and send a signal to the alternator via a varying voltage signal, which tells the alternator how many amps to generate.    Shouldn't need to upgrade that other than to prevent voltage drop issues.   You could cut the wires short and splice your own wires close to the plug if you're wanting to be consistent across your entire harness

[gzig5]

the voltage regulator doesn't carry any serious current.  It's job is to sense the system voltage, and send a signal to the alternator via a varying voltage signal, which tells the alternator how many amps to generate.    Shouldn't need to upgrade that other than to prevent voltage drop issues.   You could cut the wires short and splice your own wires close to the plug if you're wanting to be consistent across your entire harness

I think Filbert is correct, the VR is the control side and the alternator is the power side of the regulation circuit.  A corollary would be how a low current signal to the coil of a relay can control/regulate a much higher current circuit on the output of the relay.  The big wire needs to be on the output of the alternator and feeds to any circuits that are drawing significant current.

[Jay Bee]

I wonder if it would be worth a call to Bill Evans and ask if it's possible for him to make you a custom VR plug with 18 gauge wire.
http://www.evanswiring.com/default.htm

[HP_Cuda]

To answer the question on why we use heavier gauge wire like 10 gauge it's because of the resistance levels of the various types of wire. Based on the chart below the thicker the wire the lower the resistance and hence the higher the amp carrying capabilities.

https://www.powerstream.com/Wire_Size.htm

Remember your dash wiring harness is made up of mostly 16-18 gauge wires which cannot handle that much current. Over time these wires become brittle and can spark a fire like our likely suspect the amp gauge.

[dodj]

Here is my dilemma, The VR plug i purchased has 18 maybe 16 gauge wire. I used 12 gauge wire when I rebuilt the harness. Do I connect the 18 to the 12?  Do I rebuild that section at least with 18 gauge wire?  Do I try to find the barrel connectors that will work with the VR plug and upgrade to 12 gauge wire.

I would leave your harness alone. 12ga certainly won't hurt the vr cct. Get a barrel connector for 12ga. When crimping the vr connector side, strip 3 times what your normally would and fold it twice. Stick that into the 12ga barrel connector for crimping. Don't forget the heat shrink first.

[Claudia]

IMO - I always use the rule of thumb that which ever side has the larger gauge wire, that is what I go with.

If you have 12 gauge wire on your harness now and you are adding a new VR plug that has 18 or 16 gauge wires, I would not splice them together (although it would probably be okay) I still wouldn't do it.  I would take the time to convert the VR plug over to 12 gauge wire so that you do not have a wire size discrepancy going into your harness or convert your harness side wiring over to match the smaller VR plug wiring.