What decoders for a spectrum diesel ?

Hello fellow modelers, I have a few spectrum diesels in my group here and was wondering what type of decoders would work with them ? I believe some of them are decoder ready I know two out the five are not, one already has a decoder and the last two are decoder ready. Thanks in advance for any advice given.

Here is a link to the TCS installation guide photos. There are several spectrum locos in the list so perhaps one of yours is listed. http://www.tcsdcc.com/Installation_list_by_Manufacter.htm Depending on the installation there may actually be some specific decoders designed for your model (especially if you are in N scale) other wise it is a question of finding a decoder with the amp rating suitable for your loco and one that will physically fit. I suspect that in most cases there will be dozens of choices. If you list the actual models someone out there will likely have installed a decoder into that model and can give you more specific advice.

Thank you !