My mtx thunder 421d I just got has the red light staying on all the time, I have hooked up a rca converter and the amp wont play my sub, is that light supposed to be red all the time.

http://www.retrevo.com/support/MTX-421D-Car-Amplifiers-manual/id/18680ci265/t/2/
Please go to this above link, and download what you need.

Check your wiring and see that your power wire is not in contact with any part of the body of the car. I also recommend soldering the ends of all wires, to prevent them from splitting especially on the amp terminals.

If you have proof of purchase(invoice or receipt) showing the purchase date and you are still within the warranty period then yes it would be repaired by MTX under the warranty guidlines, and by the way MTX is great at customer service and they are great to work with(very fair)!!!!
Keep in mind that the seal on the bottom of the amp cannot be broken or that will void warranty coverage.
Give them a call, you will be glad you did!
800 225 5689 - MTX Customer Service & Amplifier Service Center
Good luck !

first of all you should check the minimal impedance your amp handles , if is class d it should handle between 1-2 ohms total impedance in a mono conection , meaning whatever quantity of subs you have hooked to your amplifier,their total impedance should the minimum the amp handles that way all the power from your amplifier will be used.

the amp is under to much pressure get a bigger 1

Hello jaimemm_77,

The MTX 421d is a mono amp. It only has one output channel.

If you are asking about hooking up only one channel to the input, then no, the amp will not overheat. But the output will be significantly reduced. It would be best to use a "Y" adapter with a single female and two male connectors to split the channel into both inputs.

Hope this helps.

if the lights on and there is no sound it's either a cd player issue or your rca issue or the inputs for rca's on the amp are no good. or you have your subs wired at a wrong load to your amp and it is in a constant protection to avoid burning up.

Make sure that your connection at the battery is still good-sometimes the wire corrodes up front when your system is installed for a long time-so check that out and of course the fuse that you installed a foot away from the battery so that you dont burn your vehicle down if a short occurs somewhere down the line

check your fuse up front first. some amps will turn the light on with only the remote wire (the 12 volt signal from the head unit). That may be your issue. If not you need to check your signal input. try hooking the rca's to a diffrent source, i.e. other radio your tv anything with Rca out put. If still you get nothing then pull your subs out and take a regular 9 volt battery and touch the leads to the positive and negative of the sub. Just for a moment though if the subs move when they come in contact with the charge from the battery then my last suggestion would be to take it to a store where you can have an authorized tech check out the equiptment. Good luck

Im sorry to have to inform you my friend, if you saw smoke, you burned one or more of the resistors or output devices inside the amp. Without a service manual, it will be a hard call on what exactly cooked. In alot of cases please forgive me for saying so, but the ampis not worth taking into a repair shop to be repaired, because of the high cost these days of labor. Its too bad there are no user replacable parts inside of these amps. Good Luck. Ps Please do not forget to rate this thread?