need a look under your hood please

Hello All and thanks in advance ok I have a 1992 chevy k2500 H.D. 5.7 (350 gas) with a boss snowplow I bought the truck a couple of months ago looks good runs great plow came with truck. Started using plow and after lifting plow 8 or 9 times voltmeter on dash drops to about 9 volts and truck stalls, but starts right back up like nothing wrong (very annoying) and takes a minuite to get voltage back up. Truck has two batteries but only two small wires (12 or 14 gauge) hooked up to drivers side battery, plow is hooked to pass. side (starter) battery. So on to my question I Looked at alternator wiring and one heavy wire hooked to a post with a nut (I guess bat. terminal) and a plug in with three wires coming out but the two outside wires are cut off and the center one is spliced to a single wire so only two wires hooked to alternator. Asked the former owner he said "the original alt. blew up and caught fire " so he had it replaced. so I need someone to look under thier hood please and tell me if they only have two wires at the alternator if so I guess it is right and just something to live with thanks again.
Jerry R

right , there is a red wire attached at the nut on the back of the alternator. This goes to the battery via the power block on the back of the firewall. Then there is the "brown" wire, which who knows what color it is on your plug and it goes to your voltage meter. I would have that second battery hooked up with a nice thick piece of wire so you get a good amount of juice through it.

The alt wire is a 8AWG resistive wire for safety. If the diodes ever go out in the alt, the wire is supposed to burn up instead of draining the battery. Dead battery or wire on fire, you take your you choice. It can only carry about 50amps from your 100-135amp alt. I added a 4AWG wire from the alt (+) to the (+) battery and from the (-) battery to the chassis for ground and now everything works much better.