Butt Splice (Mouser 644-BS18-M) - You will need 2 Ring Terminal or Butt Splice connectors. These are commonly crimped onto electrical wires in order to make electrical connections. Get terminals which are color coded red which means they will fit #18 size wire. The ring size does not matter as it will be cut off.
1/16" Heat Shrink Tubing (Mouser 5174-11161) - used to keep nichrome wire insulated from adjacent wraps around the eyepiece holder.
Instructions:
1. Stretch the nichrome wire out and measure the resistance from one end to the other with an Ohmmeter. If it measures 17 Ohms or more proceed to step 2. If less than 17 ohms it will not work.
2. Twist one end of the nichrome wire to one of the copper wires that will become the heater cord. Insert into a Butt Splice and crimp. For increased reliability, solder the joint after crimping.
3. Attach one Ohmmeter test lead to the end of the nichrome wire that was connected in step 2.
4. Touch the other test lead to the end of the nichrome wire and move it along the nichrome wire until you find a point where it measures 17 Ohms.
5. Cut the nichrome wire about a 1/4" longer than the point where it measured 17 Ohms.
6. Cut a piece of Heat Shrink Tubing about an inch longer than the nichrome wire and slip it over the nichrome wire. Apply heat to shrink the tubing.
7. Wrap a few turns of electrical tape around the eyepiece end of the Star Diagonal (as shown above) to insulate the wiring from the metal Star Diagonal.
8. Wrap the heat shrink covered nichrome wire tightly around the star diagonal as shown above.
9. Cut back enough heat shrink to expose 1/4" of nichrome wire and twist it to the other copper wire of the heater cord (see above). Insert into Butt Splice and crimp. For increased reliability, solder the joint after crimping.
10. Wrap remaining portion of the nichrome wire around the Star Diagonal so that the entire length of nichrome wire is in contact with it (see above). Wrap electrical tape around the nichrome wire to insure it does not slip out of position.
11. Using an Ohmmeter, recheck the heater resistance to insure it is about 17 Ohms. If it reads much lower then you have a short.
12. Wrap the heater with insulation to reduce heat loss to the atmosphere.
13. Wrap the outside of the insulation with black electrical tape.
13. Install an RCA plug onto the heater cord (polarity does not matter) and you are finished.
NOTE: To allow the diagonal to be neatly stored in your eyepiece case, simply wrap the heater cord around the focuser end of the diagonal.
