20 Most Recent MTX Thunder 421D Car Audio Amplifier Questions & Answers


Connect the remote turn on to the blue wire w/white stripe coming from the head unit, NOT the solid blue wire which is the antenna turn on.

MTX Thunder 421D... | Answered on Aug 11, 2013


The LED should be red. If you are not getting power to the sub, make sure the speakers are connected properly to the amp. Also make sure that the gain control is turned up. If it is all the way down, you will not hear anything from the sub(s). If none of that works, it is possible that you have a blown sub. If you smell a burnt smell near the speaker magnet, there is damage to the voice coil in the sub.

MTX Thunder 421D... | Answered on Mar 07, 2011


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.

MTX Thunder 421D... | Answered on May 26, 2010


that first number most likely is 2N414A. Goto NTE cross refference web site and put this number in, it will show you a cross for it with a picture of the transistor to match it to the one you have. Hope this helps good luck.

MTX Thunder 421D... | Answered on May 25, 2010


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 !

MTX Thunder 421D... | Answered on Jan 31, 2010


the amp is under to much pressure get a bigger 1

MTX Thunder 421D... | Answered on Nov 18, 2009


yep no good not worth fixing have that same prob with a few of my customers replace it you better off

MTX Thunder 421D... | Answered on Jun 26, 2009


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.

MTX Thunder 421D... | Answered on Jun 16, 2009


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

MTX Thunder 421D... | Answered on Jun 04, 2009


that means that you have a short in the power supply or in the output circuit.

MTX Thunder 421D... | Answered on May 21, 2009


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?

MTX Thunder 421D... | Answered on Oct 16, 2006


THE GREEN LIGHT SHOULD SHOW WHEN AMP IS POWER UP AN RED WHEN IN PROTECTION MODE

MTX Car Audio &... | Answered on Sep 12, 2019


Try eBay Often available there from private sellers

MTX Car Audio &... | Answered on Aug 25, 2019


I was having a similar issue. I checked every wire from the battery to stereo to amp, checked the ground, pulled the stereo to double check the wiring was all correct. Everything seemed good so I thought it had to be my battery not putting out enough power. Tested it and it was good. What it turned out to be was the connection from the power cord to the battery. It had a tiny bit of built up corrosion that was making the amp go into protect mode. Cleaned it up and hooked it back up and has been golden since.
The link attached is pretty straight up on what you need to check for different circumstances. I'm guessing it's a low voltage issue. Good luck

MTX Car Audio &... | Answered on Aug 23, 2019


Check the wiring 1st then go down the line...Check speaker connections..Look at your power,ground and remote wire hook up

MTX Car Audio &... | Answered on Oct 18, 2018

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