1) A ring around the base of the penis made with #6 solid copper. This is electrical ground wire from hardware or Home Depot.
2) A small oval contact directly under the tip of the penis made with soft brass. I used sheet brass from a hobby shop but have also used a plain penny. Drill some holes to allow thread to pass through.
In order to keep things in place I made a simple waste band with elastic and sewed a small strip of elastic around the ring to attach it. I then added a loop of narrow elastic that passes around behind the testicles to help hold the ring firmly in place around the base of the penis.
Obviously you will need to fit these components to suit your own measurments.
Solder a lead wire to each piece and attach to your choice of electronics. I use a TENS purchased for $15.00 at a yard sale over 10 years ago which works fine to this day. You will need to experiment with both the polarity ( which wire connects where ) and with settings on your particular unit to obtain the best results for your own pleasure.
The nice thing is this is a compact package that I find can be worn for a long time...even under clothing in public if you dare !!!
In place of the base ring I have also experimented with an anal probe made with 1/4" od surgical tube around which fits a 1/4" ID copper tube fitting. Make sure your connections are smooth and clean to avoid any possible tissue damage. Clean the device with alcohol and lube with KY or similar lubricant. I found this is quite enjoyable although more invasive and less convienent.