Help with system install

Friend and I are installing a system in his deck boat. The radio only has one set of preouts so we have used y splitters and ran one set of rca's to a two channel amp and the other set to a mono amp. The two channel amp is running 4 speakers in parrelle and the mono amp is running a sub. When we installed the system we added a new battery which powers the amps only, radio still runs to original battery. (will eventually put radio on new battery just haven't yet. Will need to get longer power cables first).

At first we ran remote wire to wire nut then split to each amp. When you turn on the radio the mono amp wouldn't turn on. So we daisy chained remote wire from one amp to the other and it still wouldn't turn on. To trouble shoot we hooked the remote wire directly to mono amp and it turned on and ran just fine.

At this point we figured the two channel amp was somehow over powering the remote wire so my friend found a separate remote wire coming out of radio which would allow both amps to turn on

However now when u turn the system up 1/4 of the way the mono amp cuts out (protection mode I guess, power light stays on). But if u disconnect the two channel amp it runs just fine.

Any guess where to start trouble shooting?

Might need a relay for that remote wire. How far is the run?

The mono amp could be cutting out for a number of reasons. What gauge wire are you using for the power/ground? What's the model of the mono amp and battery? If I were to guess, the mono amp is cutting out because it's trying to pull too much current through a small power/ground wire. It could also be that you're battery is not big enough and the amp is going into protect mode because of voltage drops. OR, the preout voltage on your headunit may not be sufficient. If you have an RCA out on either of those amps I'd remove the splitter and daisy chain the 2 amps.

And I'd get that headunit running off the same battery as the amps. Using the headunit on a different battery than the amps are on will cause issues. Run the power/ground from the head unit and tie it in to the power/ground on the larger amp. You can run the constant wire to the battery itself to retain the settings on the headunit (only necessary if you have a cutoff switch on the power wire before the amp). Use a toggle switch for on/off.

The mono amp is an alpine mrp-m450. We are running 6 Gage power and 8 Gage ground (I know we should be running same size but we found an old amp kit for free). The power wire Is actuly to big and was hard to fit it in the alpine The battery is a commercial 12 volt battery used on cell phone towers they are rated at 145 amp/ hours and weigh 110 pounds. I have the same type battery on my system and they work great. So I don't think it is a battery issue. The head unit is a piece of crap so it could be a precut voltage problem like you mentioned. How can I test that?

As to the remote wire run it is only about 4 feet

Also the amps do not have pass through so my only option is the y splitters

Well that's your problem right there, the power/ground wire. How far are the amps from the battery? You should have at a minimum 4awg to a distibrution block by the amps and 8awg from the distro to each amp...same for the ground.

As for the preout voltage, if you have to turn your gains way up to get good output you're preout voltage is low. I don't think this is your problem though. Fix the power/ground wire first.

i had this problem before with my houseboat as the head unit was run off of seperate source power than the amps which ran off an inverter. make sure the remote turn on for the amps and input power for the amps are tied to the same battery system. my guess is if you connect the amps to the same battery as the head unit it will work just fine as the source for the turn on will be the same. you can test this by disconnecting the existing turn on from the h/u to the amp. then just run a jumper wire from where the 12v goes into the amp from the battery to the remote turn on point on the same amp. All a remote turn on does is send 12v to the amp to switch it on which you will be doing directly from the battery versus the head unit. If it works for you as it did me, my solution was to wire a switch from the same battery as the amps to turn them on/off instead of using the head units remote turn on lead. good luck.