Thanks for the info. I'm starting to understand how the ballast work. Looks like the sample from a small HPS lamp I was checking out with the DMM is a Reactor Ballast. Searches on any of the ballast types pulls up a lot. Found a good read at: https://www.cooperlighting.com/s/technical-support/pdf/ballast%20rundown%20streetworks896e.pdf there is a schematic of the Reactor Ballast in this .pdf The ohm reading I got match this one. Turns out the HPS ballast provide a high 2500 volt pulse to start the arc. On the next street over from my house there is a HPS street lamp that comes on for a bit then off and restarts. The .pdf above covers this in case anyone is curious why HPS lamps do this.

 

In most cases, high pressure sodium ballasts and pulse start metal halide ballasts in our country use a 3 wire impulser ignitor that has 2 wires connected in parallel to the lamp and use a third wire for using the choke component as a pulse transformer to step up the pulse voltage to allow for 2500v to 5000v pulses to strike the lamp. In other countries, some ballasts use ignitors that have 2 terminals connected in series with the lamp and use a third terminal that is connected to the lamp socket's neutral. Those ignitors are known as superimposed ignitors. They use an integral pulse transformer to provide high voltage pulses to any lamp. An advantage of superimposed ignitors is that they can be used on any ballast that is able to provide the voltage that is needed for such ignitors including ballasts that do not use an ignitor tap for an impulser ignitor such as mercury vapor ballasts. Superimposed ignitors are commonly used in tanning beds in our country and are typically used in countries that use 220v-240v mains for most applications. Lastly, there are 2 wire parallel ignitors that simply have their wires connected in parallel with the lamp. I believe those ignitors work by using an internal pulse transformer that simply steps up the supplied voltage to a much higher voltage between 750v-1000v for igniting probe start metal halide lamps on mercury vapor ballasts and between 2500v to 5000v for igniting pulse start metal halide lamps and high pressure sodium lamps. 2 wire parallel ignitors with 750v-1000v pulses are typically used in countries with a mains supply between 220v and 240v because they use probe start metal halide lamps on simple choke ballasts. Since 220v-240v mains is not high enough for the reliable ignition of probe start metal halide lamps on a choke ballast alone, they use the 750v-1000v 2 wire parallel ignitors for reliable ignition on such mains voltages. In rare cases, 2 wire parallel ignitors with 2500v to 5000v pulses are used for igniting high pressure sodium lamps and pulse start metal halide lamps. Those ignitors largely fell out of favor in most countries because the high voltage pulses from such ignitors would damage the insulation on the ballast windings. I believe the reason as to why 3 wire impulser ignitors were developed was to use the third wire to discharge the high voltage pulses from the ignitor in order to protect the ballast windings from high voltage pulses.