Hi Guys and Ladies,

I have a 1967 Plymouth B-body with a trunk mounted battery. The battery is not charging properly when the car is driven. We have tested the alternator (2-field) and it is outputting over 14 volts (14.4 volts I believe). When the car is running (idle and 3k rpm), we are only seeing around 13.45 volts at the battery. I do not think 13.45 volts is enough to charge an Optima red-top battery (or any car battery for that matter).

My questions are:
1.) What size positive wire are people running from the front of the car to the battery in the trunk? It appears the wire for this car is 4 gauge, which I think is too small.

2.) The positive wire from the battery is run up to a bulk-head on the firewall (not the factory bulk-head). It appears to be a stud or bolt that the battery wire, starter wire, voltage regulator (I think), and alternator charging wire (12 gauge) all connect to. What are other people using as the wire junction?

3.) A friend of mine has recommended I try an adjustable voltage regulator. Has anyone gone this route? If so, did it work?


Thanks in advance for your advice and input.

A couple of comments... with 13.45 volts it is at least charging. Without charge it would be under 13 volts. The main wire to the trunk (4 guage) is on the small side for starting purposes but plenty big for the alternator current. If it starts OK I wouldn't worry about it. The standard MOPAR voltage regulator is temperature regulated... as the engine compartment and regulator get warm, voltage drops. 13.45 volts isn't unusual for a warm engine compartment/warm regulator. I bet if you watch it, voltage will be highest a minute or two after the engine starts then taper off.

Voltage drop from the alternator to the rest of the wiring is likley mostly in the 12 guage wire from alternator to connection point. The voltage regulator increases alternator voltage to compensate but a larger guage wire - 10 guage at least, bigger if you may upgrade the alternator - from the alternator to your connection stud would be a good idea.

From your description, the stud setup sounds OK as long as nothing is chafing or rubbing. A pic would be interesting. PS: on mine I run the battery wire to the starter with a 6 guage jumper wire from the starter to the starter relay. Basically I use the starter relay stud as the main junction including the charge wire from the alternator.

I run an Optima in the trunk also with MOPAR voltage regulator. Voltages are similar to yours. The first Optima performed perfectly for 7 years. I'm on my second now.

Bottom line, as long as connections are clean and tight and nothing is getting hot I wouldn't sweat it.

Battery is 12v and 13+v is fine to charge it.

I'd change the 12ga to 8ga or 6ga and the 4ga to 1/0 or 2/0. No need for an adjustable reg & the stud bulkhead is fine just want clean connections all the way around on the positive/neg circuit route

Thanks for the advice. I've attached a picture of the stud located on the firewall.

I forgot to mention:

The car starts fine, as long as the battery is charged.

In the picture, the large cable running to the "left" is the positive cable to the battery. The large cable running off to the "right" is going to the starter. The little red wire with the yellow crimp-ring is the alternator charging wire. It was originally about a 16 or 14 gauge wire (red wire in picture bent back to the "left") and we changed it to a 12 gauge to see if it would make a difference; it did! So, we will go up in wire size to an 8 or 6 gauge and see how that works out.

Thank you all for the help!

Jon

Sounds good. If you are having starting problems with a less than perfectly charged battery, it may be the cables to to the battery are too small. 4 guage is OK for short cables in the engine compartment but not normally enough for handling starting current with a long run to the trunk. I run 1 guage which works fine. I believe Robert suggested heavier. Either way, 4 guage is on the light side for that long a run.