RV Repair: Hooking 12 volt batteries in series, 12 volt batteries, auxiliary batteries

Question
I have an 88 Mallard Class A coach that I am trying to replace batteries in.  I have the main chasis battery for starting the coach and to deep cell marine auxiliary batteries.  There are also two wires that are connected to both sides of the isolator switch which allows the coach to use the auxiliary batteries to start the coach if the main battery is discharged.  How do I hook up the batteries in series.

Answer
•1
Set the two batteries next to one another, arranged so that the negative terminal of the first battery is next to the positive terminal of the second.

•2
Attach a jumper wire from the negative terminal of the first battery that is next to the positive terminal of the second.

•3
Attach the negative lead from the device you will be powering to the negative terminal on the second battery.

•4
Attach the positive lead from the device you will be powering to the positive terminal on the first battery, and you are finished. These two 12 volt batteries will now produce 24 volts to your device.