Yaesu FT-225RD is a good looking older rig. Not much in terms of accessory ports so here are some considerations.
There is a “Tone In Plug” which would be a desirable connection point.
Some relevant info can be found here.
Assumptions/notes:
- GND is the connector’s shell (reasonable and unavoidable if rear panel is conductive)
- TONE IN (pin #2) is audio input to the radio
- PTT (pin #3) is PTT input that activates the transmitter when grounded
- SP - sounds like speaker, but may be S.P., no info on what that is/does and why would it needs a jumper. See what happens when jumper is removed (no PTT from mic? no audio from speaker?). For extra credit scope when connected and each side when disconnected.
If that all checks out then connections are:
- GND → 3.5mm TRRS sleeve
- PTT → 3.5mm TRRS ring 2
- TONE IN (audio input to radio) → 3.5mm TRRS ring 1
- SP 3.5mm TRS tip → 3.5mm TRRS tip
The less desirable, but reliable fallback option is to tap the mic:
- MIC pin 1 GND → 3.5mm TRRS sleeve
- MIC pin 2 MIC → 3.5mm TRRS ring 1
- MIC pin 3 PTT → 3.5mm TRRS ring 2
- SP 3.5mm TRS tip → 3.5mm TRRS tip