Matt,
The numbers I initially gave you were a bit on the high side, and your numbers indicate that your alternator is functioning about as well as can be expected of it. I do agree that you may have a bad/weak connection between the alternator and the battery. With the engine at full rpm the battery voltage should read the same as the alternator output as long as there are NO lights or other loads on, provided that the battery is okay. Your numbers indicate that the battery is probably okay. The real problem you have is that you're expecting more from the OEM alternator than it is capable of delivering. As you noticed, when the lights are on the voltage drops precipitously - that is because the alternator simply does not have the capacity to handle the load you're putting on it with the lighting.
The OEM alternator is just barely adequate to keep the battery charged, but it is not sufficient to keep up with even just the headlights on. It only puts out somewhere around 10-12 amps at full output, so a pair of 65 watt headlamps uses all it has and then some, by the time you figure in line losses and such. Add in the taillights, brake lights, dash lights, work lights, etc, and you're going to gradually drain your battery, even though your alternator is working its little heart out.
If you plan to use your lights much, or that electric chute motor(you'd be surprised at how much current even a small motor draws), or any additional lighting, you really need a much bigger alternator. Fortunately, it is easy and inexpensive to achieve that. I replaced my OEM alternator and regulator with a 65-amp Delco 12Si alternator. The Delco 10Si and 12Si alternators are internally-regulated units so you don't need a separate regulator, and they're available in either a 1-wire or 2-wire (also sometimes called 3-wire) configuration. I opted for the 2-wire configuration since those begin to charge at a somewhat lower rpm due to being externally excited. The 1-wire units are self-excited so they don't develop full output until they're turning at about full engine speed on a diesel tractor.
I got my Delco alternator on Ebay for about fifty bucks and also spent another ten bucks for a voltmeter to mount in the dash, since the new alternator has too much power to run it through the OEM 35-amp ammeter in the dash cluster. I simply ignored that, installed the alternator with the excitation wire coming from the key switch "on" terminal and the output going directly to the "+" terminal on the starter where the battery is connected. I cut the wire that fed the OEM voltage regulator and capped it off. Since the new alternator is not feeding through the ammeter, it now only reads the amount of discharge from the battery for lights or other loads, which is fine with me. I know my battery is being charged as it needs it, since the voltmeter tells me what the alternator is putting out at any time. (grin)
The Delco 12Si alternator matched right up to my TY395 engine in my Jinma 304, all I had to do was swap the pulley from the OEM alternator to the new one and modify the support arm to position the alternator in a slightly better position. While I was at it I replaced the OEM V-belt with a new link belt from Harbor Freight. Took me just about three quarters of an hour to do the whole mod and now I can run the headlights, two pairs of work lights and a fan all at once, and still have capacity left over. I can also run my 2000 watt inverter when I need 120 volts in the field.
