I have dual batteries that I plan on hooking up.
One is a regular battery and the other is a Deep Cycle.

My winch is hooked up to the Deep Cycle.

How do I join the two batteries?

Hook the positive from the Deep Cycle to the regular battery?.

Run a ground cable from the negative post on the regular battery to a bolt on the engine?

I do not have an isolator.

This is just a temporary setup as I had an isolator but it was faulty.

I'm leaving for Moab tommorrow and do not have time to get another isolator now.

you can wire them together like you want but I would set it up so you can disconnect them, as long as the alternator is running the differences in the batteries will be minimal, the problems arise when the engine is off, the stronger battery will attempt to charge the weaker battery resulting in both going dead. what battery the winch is hooked to is irrelevant with this setup, you will draw from both for winching and starting as they are wired in parallel.
if your starting battery is already hooked to the vehicle I would just connect the batteries to each other positive to positive, negative to negative, just remove the deep cycle positive clamp when you stop for the day.

If your charging system is in good shape, you have nothing to worry about . Just run a positive from secondary to primary. Then run a ground to the secondary, or just to a ground on the frame. I have been running this set up for over a year without a problem, but if you do leave the lights on or something like that, both batteries will go dead.

:skull: