First off you didn't say which car this would be on, but concidering you did say saddle packs I will assume it is in a classic 2 belt car (IE:X-Ray,414M, Pro 2)
First a little soldering info..... ALWAYS, ALWAYS, ALWAYS pre-tin the parts you are working on, once they have been tinned you will add NO, I said NO extra solder. You pre-tin the parts by applying the heat, and every so often tab the end of your solder on the metal, not the iron.... do not apply solder to the part until it begins to start flowing onto the metal/ wire. once it begins to flow you will apply a liberal amout of solder, on the wire make sure all sides have solder on them, it should look like a ball of solder on the end of the wire, and you shouldn't be able to make out any strands of wire.
Second- on the ends of your wire you really only need 1/8" or 3-4mm of wire exposed from the wrapping.
Third- The thinner the solder you use the faster it will begin to flow for you, I use the absolute thinnest wire possible I believe like 0.065".... And get rosin core solder....... NO other soldder should be used, and seperate flux should not be used, besides it just looks $#!tty!!!
Now for layout time- place your battery, motor, speedo in the car just the way you want them, try to place speedo on the chassis at a position in which the + wire gracefully flows to the + battery tab of either the motor or battery which ever will be closer, you also want to avoid any U bends in the wiring (for no other reasoning than ease of wiring..... mount them solid.
Wiring layout, now lay the wiring out starting at the + terminal on your speedo, flowing gracefully over the + terminal of the next closest connection (battery or motor) and finally to the farthest + terminal, once you are satisfied with the results take a sharpy marker and make marks on the wire where the wiring will need to come into contact with the + terminals allowing for slack to make life easier, especially for you motor connection because it will move as you change your gearmesh.
Now it's time to strip back the insulation, at the beginning and end of the wiring you will only need to expose 1/8" or 3-4MM of wiring any more will just make for an ugly job... in the center of the wire you will need to cut spirally around the wire in 2 places and then slice lengthwise between the 2 cuts to be able to peel away the insulation.... This openning should be about 1/4" or 4-6mm. Pretin the wiring making sure that all sides are covered in solder. Now pre-tinn the electrical connections of the speedo/motor, battery.
Now heat the first connection, usually the speedo, once the solder on the connection begins to flow you will quickly place the soldered end on of the wiring into the molten mix, you donot have to remove the heat, BUT DONOT touch the wiring to the iron, only to the connection, DONOT place the wiring into the molten solder and then put the iron ontop of the wiring and crush it down!!! it will not make for a better connection and it will start to look like chicken$#it..... Do the same with all of the electrical connections to the end of the wiring.
Now do the same with the - battery lead and the -motor lead....
Doing a professional solder job on your car is 50% in the preparation, 40% in the skill and 10% in the equiptment.....
I will try and post a few pics to kinda give a visual....... As all things practice makes perfect, buy plenty of wiring and rewire your electrics every other day until I get it right 100 times in a row.......LOL J/K.........(or am I