connecting gps, radar audio to headphones

Im using a Y spit male mono to female stereo 3.5mm cable and attaching my headphones figuring that each device would be on a seperate seperate channel.  Im getting stereo from both units when there connected, is it possible to diode isolate to solve the feedback?

The cable I'm using is  two seperate MONO male 3.5mm Y'd into the female 3.5mm stereo audio jack...so there is a left and a right input  to the stereo plug.  I would have thought that diode isolating each mono input would have solved the feedback issue.

Both of your units have a sterio jack. What youll need to do is get 2 sterio cords. One to plug into each unit. The other end youll cut. There will be 2 wires in each. You will splice those 2 together. On your headphones, there will be a jack. Cut it off. There will be 2 wires. Wire one wire to the one unit, wire the other wire to the other units wire. You can also use mono type cords then you wont need to splice those wires together. Hope this helps:

Here is the actual cable:

http://www.cablestogo.com/product.asp?cat%5fid=2009&sku=03182

The gps is a stereo unit..the radar is mono.  When both units are connected there is feedback through the other unit causing the each mono input to be heard on both lft and rght channels in the headset.