Test your DCC decoders before installation by following the manufacturers’ recommendations.
Some manufacturers include basic test kits with starter sets; you can easily build your own decoder tester or purchase one of the commercially available models. You can save yourself a lot of troubleshooting time if you perform this test first to be sure that the decoder you are installing is working before you put it in your locomotive. You can do this test for new decoders and for ones that you are moving from one locomotive to another.
You will need a test lamp and a protection resistor to perform the test. Instead of using an actual motor, locomotive lights and functions, use a test lamp to be sure the decoder is functioning properly. Use a protection resistor to avoid any damage to the decoder caused by wiring errors.
If you are a first time installer, this procedure will have the added benefit of familiarizing you with the decoder wiring before you do the installation