The Z2 decoders with wires are used for the AZL locomotives with four digits order numbers and the Budd RDC. These locomotives are DCC prepared. They have six soldering pads which are then connected with the wires to the decoder.
The newer AZL locomotives with five digits order numbers are prepared for drop-in decoders. Two drop-in decoders are available: DZ123Z0 from Digitrax and AZL4 from TCS. Both have SMD LEDs on board for the head and back lighting. The drop-in decoder of my choice is the AZL4 because it has two additional functions that can be used for illuminating the headlights. Additionally, it has soldering pads for connecting directly a LED without a resistor parallel to the front LED on the PCB. This is not described on the decoder information sheet, but it is obvious when looking at the printed circuit board. These additional features are very helpful for a good illumination of the headlight as the newer AZL locomotives have only very weak headlights.