This may be a very dumb question but this is the first time i've fitted an amp so here goes. I have a Alpine IDA-X200 headunit with a brand new Alpine MRP-T222 2 channel amp, i've wired up the amp to some new Hertz components in the front so far so good.
The problem is i want to drive the factory rears off the head unit and the fronts off the amp, if i just have the RCA cable plugged into the head unit the amp powers the fronts lovely, if i then however plug in the factory speaker plug into the headunit to power the rears the fronts stop workings? the only wires connected to anything on the factory plug are the rear speakers?
Do i need to disconnect the front cables from this plug so the onbly ones left are for the rears?. The head unit has outputs for front/rear and subwoofer so does this mean i cant use an amp for the fronts and head unit for the rears?
Something sounds amiss to me
I had the same head unit as you in my Mazda. You should be able to use all 4 channels from the HU as well as the pre outs, on their own/all together without any problems.
There is a setting on the HU to switch the sub pre out on and off, make sure they are on. Hold the setup button until you go into the options menu and scroll through untill you get the right setting. Have you got the manual for the HU? If not you can download it from the Alpine website, let me know if you need a link.
I'd go over the wiring again if I were you and double check it's all as it should be. Are you using an ISO connecter to the original wiring in the car? If so that will power the front speakers from the HU. You will have to disconnect them and run some additional wiring to the speaker from the amp. Don't connect them up to the original car wiring.
Just as a check how have you wired the amp? You should have it wired as 12v+ direct to the battery via a 30amp fuse. 12- to the chassis somewhere and the remote to the blue and white wire on the back of the HU. Sometimes called antenna wire as it operates an electric aerial.
Then RCA's from the rear of the HU to the AMP. Make sure you use the outputs in the rear of the HU as it has and input side too.
Then Speaker wire from the amp channels to the speakers you want to power.
Sorry if I'm teaching a granny to suck eggs. Just want to make sure you've got it right
If you still get problems there might be a fault on the HU itself.
Take some pictures of the wiring set up, would help loads to see how you've done it.
Let us know how you get on.