1999 Toyota Avalon, Alpine with OEM amp?

Ah ok, I guess with all those accessories if you were using them often without the vehicle running a 2nd battery properly isolated will definatly help prevent getting stranded from a dead battery.

However if the vehicle is running and it did harm to the batteries you might have a weak charging system. The only real way to harm battery(s) is to continually run them down (aka deep cycling) or just getting worn out from age. Remember , once the vehicle is running the load is on tha alternator to run everything as WELL as charging the battery so adding another one will actually place more load on the charging system. If you are damaging them by running them down may I suggest using deep cycle battery, aka "yellow tops". A bit more money but designed to be deep cycled so they last alot longer.

If there is a chance you are exceeding the current demands of the stock charging system a high output alternator is the solution. However none of the components you mentioned really seem to be very high current...even combined. But all in all, you are using an isolater which is the correct way to add a batt. so it can't really do any harm to have the extra starting current (remember the batteries MAIN purpose is to start the vehicle, after that the charging system really takes on all the work, otherwise your vehicle would never start...right?

Gobble as well but don't eat too much..ah what the heck stuff your face, I know I am.

Ok I understand better what you are doing..very cool BTW.

Anyhow, if the batts are dropping below 12v (theoretically a "perfect" battery should be 12.66 volts) there is a problem. Most likely the batteries have been deep cycled too often...according to MECP it is stated that everytime you deep cycle a standard lead-acid battery it's life expetency is reduced by up to 50%. So you can see that it doesn't take too many deep cycles to destroy a standard battery..add to that natural wear with age.

Now if you experience this voltage loss with good batteries and everything is off you could possibly have a current draw problem. If you don't know how to do a current draw test you will need someone to do it. 7 to 10 milliamps is the norm...up to 20milliamps is safe. After that expect dead batteries in the morning, regardless of what type. Even something as small as a relay sticking will draw 150ma overnight...more then enough to kill it.

With what you stated about leaving all that equipment on 24/7 you really have no choice but to use deep cycles IMO because they are going to be drained often and in the long run it will save you money and headaches. This is a primary reason they are used in boats, RV's etc. You are basically giving the batteries the same use as those mentioned and they are designed for that kind of use for longer life.

I would recomend to wire the isolator in a way that they will both be charged via the alternator..but when the key is off only 1 battery gets used. This way you have the safty margin of at least one charged battery at all times to start the vehicle. If you don't know how to set up the isolator to operate in this fashion post a pic and some info on it and I will help you out if possible.

Ok according to those images the vehicle is utilizing a non amplified harness..which you will use the 70-7061 toyo harness. Now if you are 100% sure the vehicle has a factory amp you can probably get away running it high level..in other words connect the speaker wires of the aftermarket deck directly to the metra harnesses, connect both blues (one is power antenna remote, one will turn on the factory amp if it has one). Now if you don't have a power antenna or factory amp you can still connect the blue wires, it won't hurt anything.

Yeah I know those dash clips can be a little tight..especially when "virgin". As far as the other plugs ,modules, denso thing etc that is all HVAC controls, nothing to be concerned about as long as you don't forget to plug everything back in when done. Your New headunit will bolt right onto the factory brackets and reassemble as reverse. If your new head unit is single din you can use a metra univeral pocket kit to fill the space..about 19-20 bucks tops.

As you stated in your original post if you need to drop the input level you can use a 4 channel converter to do this. But I would bypass the amp if that's the case but it's up to you. You have one on order regardless..a bit pricey but it will work.

As far as the isolator it looks like you have everything in order...done safely and reliably.

One other thing. Although I doubt this will be an issue if the speaker level input is too hot (if there is actually a factory amp) you have another option as well.

Instead of using a converter or hacking the harness you can do this...

Hack up a set of RCA's and splice the ends onto the metra harness speaker wires. This will give you a line level input without hacking the car. Now keep in mind there is no way to predict if there is enough voltage to give you enough volume but it is very worth a try. Your only risk is an RCA cable that you cut. Put the center wire of the coax to the positives (solid colors) and the shield (copper braid) to the negatives (striped), The metra harness will be color coded to match the alpine exactly so it's a no brainer. If done this way you will not use the speaker wires from the deck..insualte those off and plug in the RCA's connect the remotes and check the sound.

However I still have some doubt if theres a factory amp. Perhaps it was an option and not all have them. I will look at the images again and see if i notice an amp on the deck.

Keep in touch with the progress and best of luck.

yeah it looks to me like a large heat sink is on the back of the deck..this would identify it has an internal amp in most cases.

One way to check for sure is this....when you get the metra harness take a small battery like a 9v or D and touch the positive and negative to a pair of speaker wires for a second and see if you hear a popping noise, if you do there is no external factory amp. when you do this make sure the yellow wire from the metra harness is insulated...it is constant power and could blow a fuse if it touches anything..or use the harness that has the rear speakers on it to test, that is the one without the yellow wire.

ok cool.  yeah I thinks it's brown as well because I know for a fact one of the factory colors for a speaker wire is black on toyotas and i don't recall seeing 2 blacks wires.

But I guess not having an external amp is good news..less money..less work...less chance for problems..and more or less what you were looking for. The alpine will sound great as long as the speakers are not shot.

Anyhow you just need to find a pair of speaker wires to do the check..you don't need power or ground..I believe the factory colors are as follows.....pink and purple               light green and blue

red and white      black and yellow

this is off the top of my head but i am about 99% sure. Once you get the metra harness it is standard color code to the alpine so it's very simple to hook up electrically.