I probably have this theory wrong, but it's my understanding that ignition wires are engineered with some resistance which allows the voltage to build slightly which results in a stronger spark. This also happens when the voltage reaches the electrode on the plug...it builds until it has sufficient strength to jump the gap.
Because you are using solid core wires, they might not have enough resistance to allow the voltage to reach a adequate level for the inductive pickup to read.
I know the inductive pickup on my timing light has a big warning label on it not to drop or slam it...it's rather delicate. Could your pickup be screwed up!
When you pull the plug wire and the light works, I think you are creating artificial resistance in the wire and the pickup and sense it and the light triggers.
I might be all wet on this theory...lets see what the guru's have to add.
I have more than 10 years experience as an electronics technician, and I see a few flaws in theory in your post.
1. Everything presents a resistance to electrical current. Even 'super-conductors'. The quantity of the resistance is what makes the difference. In a series circuit, like an ignition system, resistance will always cause a decrease in both voltage and current, but the characteristics of the spark plug wires, unless you are using coat hangers as substitutes, is usually not a factor.
2. Actually, while the points are closed (electrical short) battery current charges up the ignition 'condensor'. When the points open, the condensor discharges through the coil because there is no other path for current. The coil is a transformer, as mentioned before, and converts the 6 or 12 volts, at relatively high current, from the condensor, into 10,000 to 100,000 volts at very low current, and sends it to the center connector of the distributor cap, where it is distributed in accordance with the position of the rotor. (The low current is what keeps us all alive. Voltage does not kill. Current does. More than 1/2 amp of current can kill you. the CURRENT through the spark plug/wires/gap is only a few milli-amps. The high voltage is required to jump the air gap between the spark plug electrodes. This air gap represents a large resistance.
There is absolutely no reason for a stovebolter to know this much theory. It won't help your engine run better. Your engine must have the timing set correctly in order to run correctly. This does not require that your engine even be running, as long as you can find the correct timing mark.
All you need for fairly accurate timing is an ohm meter. If the vehicle has a battery in it, all you need is a six volt bulb with leads soldered to the threaded part, and the lead tip at the base. Set your timing mark to whatever you want. Look at the valve gear to determine when No. 1 cylinder is at top dead center. Hook your meter or test light across the points. Then twist the distributor (which I know you remembered to loosen the clamp on) until the light, or meter shows a distinct change in voltage. The light will go on, or off, and the meter will respond as expected.
Keep twisting until the transition is a fine as a frog hair, or you get tired. Either way, the timing will be good enough for the engine to run. If your carburetor and vacuum advance are any good, it will run nicely. You may do better with a timing light, but I never have except with engines that produce more than 500 horsepower.
If your coil is any good, you won't gain anything by using solid core wires. I found a 6 Volt Mallory coil on E-Bay a while back, and that is what I use to start 6 volt systems. A 12 volt coil will work, because it doesn't care. It's just a transformer. Put in 6 volts and it puts out 12,000 volts. Put in 12 volts and it puts out 24,000 volts. If your spark plug gap is anywhere near correct, you WILL get a spark.
