I recently modified the headphone jack by moving it to the back plug of the 250. I always wear headphones and I would occasionally get the wires tangled up in the armrest, sometimes yanking the headphones off. I noticed the higher end Garrett's jack at the back of the armrest, and thought that might help reduce the chance of interference. I could not find a short enough factory cable anywhere, so I bought one too long at Radio Shack. I wanted to keep the modification neat, so instead of wrapping it around the shaft and through the foam handle, I drilled an extra hole in the shaft just under the control box, cut the female end off the Radio Shack 1/8" headphone extension cable, and snaked the cable through the upper shaft and out the rear entrance. You will probably have to remove the armrest during this procedure to get the cable past the screw mounts inside. After you do this, simply reattach armrest with the two screws. The male end of the extension cable is plugged in to a 1/4" to 1/8" adapter, then use a little electrical tape to pretty things up and keep it snug. The black plug at the rear of the shaft fits snugly, but will come out with a little coaxing. I found that the female headphone mini-jack (1/8") at Radio Shack don't fit well into the black plug, so I located one made by Vanco - part #JC353 stereo 3.5 mm (1/8") female jack at a local dealer. I fits the black plug beautifully. Drill a small home in the black plug, and gradually make it larger. I rounded the hole off and sized it by using a small pair of scissors, twisting one scissor blade in the hole (from the smooth outside) until the female jack end fit very tightly. Just go slow and a little at a time. Then trim the extension cable where only a few inches protrude from the back of the shaft, strip the three wires and solder to the female jack that is now mounted on the black plug. Put electrical tape over the connections for good measure, and carefully put the plug back in the shaft.
I now have many options:
1) Use the factory speaker by unplugging the 1/4" x 1/8" adapter from the control box
2) Use 1/4" headphones by either using the factory plug-in or using another adapter - 1/8" to 1/4" inch at the rear of the shaft
3) Using regular 1/8" headphones (with volume control) either at the control box or the rear of the shaft
4) Using my wireless headphones (Scosche BTHPK). These were only about $30 on eBay and sound good. They are rechargeable (transmitter and receiver) small, lightweight and easily attached to the Ace. They also have a volume control. I used a common cell phone clip attachment to mount the transmitter to the armrest lower section. It removes easily for recharging. The headset is a "behind the head" setup, instead of on top of the head. This allows me to more comfortably wear a hat on those hot days.
I also located a Flexible LED Book Light from a local hardware store for one dollar. It has changeable batteries, but for that for that price I'll just but a few extra units. It has an on/off switch. The clip is actually rounded on the ends, easily securing itself to the shaft. I then run the flex cable between the Velcro strap ( okay, I don't use the seat belt...) which secures it in place and shines brightly on the display panel for those nights you don't want to stop detecting even when the sun goes down. It is of course adjustable.
I hope you find these little modifications helpful. They help me to have more "quality time" with my ACE 250. I use all three coils and of course, the Pro-Pointer which is great!