348 Power Disconnect Switch?

If your battery is in the rear (I can't tell from your profile), there is none. If in the front, it's by the fusebox in the trunk.

 

My battery is in the rear and there is a disconnect not far from it, on one of the uprights that form the rear shock tower. I think this was the case with the later rear battery cars, but I may be wrong. In any case, some of the rear battery cars do have disconnects-- it should be hard to miss if you do have one.

 

My 90 with rear battery has a cutoff switch by the shock tower as well.

Larry

 

Remember to reinitialize the ECU's and let them go thru the relearning process before you drive the car again. IMO a better approach is to connect a battery tender to keep the battery peaked up.

 

I am going to install a remotely controlled battery isolation switch for the two red wires that connect to the positive battery terminal. It will not cut-off the thick positive battery cable as it is not necessary (not where the drain current flows). The switch is a latching relay type (Intellitech 01-00055-000, 100 Amp) that will not draw any current whether in "on" or "off" position and it can be activated/deactivated by a switch mounted under the dashboard. There are also remotely controlled latching relay type battery cut-off switches for high currents (that can carry the starter motor current, if one wants to cut-off one of the thick battery cables) but they are quite large and expensive.
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I've used the battery shut off on my car for 23 years without an issue.