I did this on a 1990 Bronco but installation should be similar on other vehicles...


Parts Needed:
Optima Yellow Top
Optima Red Top
Hell Roaring Technologies BIC-75300 Battery Isolator/Combiner
4awg cable from backup batter7y to BIC
2awg cable from starter to BIC
4awg cable from backup battery to ground

Lighter to melt shrink wrap
Wire cutters or scissors(if you like blisters) to cut wires
Wire Crimpers or pliers you can pretend are cripmers...
Dual battery tray
I also got the remote switch, it makes things a lot easier

Tools:
Flat and phillips screw drivers
Basic Sockets

You will need to make a dual battery tray or purchase one. I tossed the stock tray and made one out of 1/2"x2" metal flat steel bars as seen here.

The two optimas fit tightly where my original battery was, I just rotated them 90 degrees from the stock manner.

1. Be sure to disconnets all battery cables before messing around with everything. After you build the battery tray, secure the batteries. I used ratchet straps, one between each batteries terminal and breather valve, and one to hold the 2 batteries together. I figure 3 1200lb straps should have no problem holding 2 batteries...


2. Hellroaring supplies pretty good directions, so I'm not going to repeat them here. I will say that you want to make sure you hook the backup battery to the starter solenoid, not the starter. Making that mistake will result in a small fire... see my oops section. I mounted my unit about a foot behind the starter solenoid Make sure you leave room for the hood hinge to swing down.



3. You will want to make sure you fully understand the directions before installing the unit. I installed mine in the basic backup wiring scheme. This way if my main battery is too weak to run a winch or start the truck, you can jump start yourself. Also if you really needed to supply the winch or inverter with more power you can, just be sure to shut off heavy loads before switching.
3. At some point you will need to cut and fit all of the wires. Pray that you have wire cutters because scissors do not cut it on 2awg wire...


4. I connected both of my grounds to this post on the block, behind the alternator. My stock ground wire way falling apart and the nut holding it on was totally inaccessable.


5. Having the remote module for the BIC seems a lot easier and I am glad I got it. Again, good directions from Hell Roaring. I mounted my switch right by my stereo.

Make sure you ground the switch to a solid part of the truck or it won't work correctly.


7. Reconnect everything when you are done and that's it! The finished product on my truck looks kinda confusing. This is mostly because I have so much electric stuff. All these wires, and I even have an extra fuse box under the dash running things...