I recently upgraded my GPS for my motorcycle touring from an (ancient) Garmin (that I really liked) to a larger-screen, free map update TomTom XL 350TM with a huge screen. I had added a chassis audio out jack to the Garmin so I could listen to the instructions from the voice commands through earbuds in my ears inside a full face helmet. I was not able to hear the speaker (only) instructions in wind, traffic noise and when wearing the full-face helmet.
The XL 350 is a very thin device when compared to the old Garmin so I wasn’t sure if I would have the necessary room inside the cabinet to add an audio jack. The first challenge was getting inside the cabinet to access the speaker wires. On the Garmin the bezel around the screen could be removed to access the interior. Such was not the case for the TomTom. The circular speaker for the TomTom is on the rear of the device. With a careful bit of prying I was able to loosen and then remove the perforated cover of the speaker to gain access to the speaker and wires. There are six tabs on the perforated cover that hold the cover in place over the actual speaker.
There was not sufficient clearance to mount a chassis-mount audio jack into the cabinet. I decided to use a 3.5mm stereo plug with pigtail fed through a small hole drilled (carefully) through the chassis into the back of the speaker. I cut one end off of an audio cable leaving a 3.5mm stereo plug on the other end. The three wires inside the cable had braided thread insulation that was removed with a match to expose the braided wire inside. Two of the three wires were combined, and soldered to the red wire of the speaker and the other wire (ground) was soldered to the black wire of the speaker.
Black electrical tape was used to carefully wrap the soldered connections to prevent them from touching each other or any part of the circuit board that was in full view behind the speaker opening.
It was wonderful when I turned on the GPS and listened to the very clear instructions through my earbuds. This modification will allow me to hear the GPS instructions inside my full-face helmet in all traffic noise.