I need to replace the battery in my '97 4Runner and I have never had the code for the radio. It wasn't in the owners manual and it was a few years after I bought it that I noticed. The dealer hasn't been helpful so before paying them to look up the code or tell me the default one, I ought to at least try replacing it as explained below. I know they know the code because they replaced the last battery and it came back fine. I'll go elsewhere to buy my next Toyota.
I was thinking that I could take my deep-cycle trolling battery (12 volts of course) and hook it up to the battery cables in parallel before removing them off the old battery. That should keep the voltage the same and power available while I install the new battery. I understand the importance if "being careful" and not shorting the connections. It shouldn't be very tough and you could probably do it with jumper cables if careful.
What do you think?