Hi Pat,
That's excellent, and I reckon we stand a good chance of resolving this problem now that you have confirmed this.
I assume that you have checked (or will firstly check) the continuity of each wire involved, both from the input terminals of the speakers to the x'over, and between the x'over and each driver. The readings here should be virtually zero Ohms, if you connect the meter's leads from one end of each individual wire to the other.
Whilst by no means essential, it would be helpful to see how these x'over parts are arranged. As there are so few components, can you draw out how the various connections are between the input terminals of the x'over, how each component is attached to the others, and finally where the outputs to the 2 drive units are in relation to this? i.e A schematic of the complete x'over.
If this isn't easy, what I suggest you do initially is to measure across each individual component in the crossover, and make a note of the DC resistance reading. Having done this, do the same with the other (good) speaker, and compare these with each other. Of course, if say you find that any component is completely open circuit (i.e. infinite resistance) in the bad x'over, then this will be where (or at least part of where) the problem lies, and there should be no need for any comparisons with the good x'over.
Personally, although I have several costly and very fancy and accurate multimeters in my tool kit, I find that a good old cheap analogue type (with a needle, as you mentioned) is much better for this diagnostic work, at least for some initial cursory checks.
You will find with caps for example that initially there will be a brief reading of sorts, which will rapidly change to (almost?) infinity, depending on the cap's value. With an analogue meter, you can readily watch the needle 'swing' from one end of the scale to the other (and try different resolution settings too), but with a digital meter, the change is too rapid for it to be displayed properly.
Reversing the meter across the cap and back again a few times, will enable you to see how this change in resistance occurs each time, and this can be compared with the known good cap from the other crossover. Unless you have a capacitance measuring facility (which I assume you haven't), this can indicate some worthwhile info on caps, especially if one has gone completely open circuit, whereupon there will be no reading at any time other than infinity. It will also indicate if the cap is internally shorted out, by showing virtually zero resistance, but in view of your symptoms here I don't think it is very likely that one bad cap would short out across both drivers, which would need to be the case from what you describe.
If any cap does show virtually zero resistance, it might be that it is in parallel with an inductor (coil) which you should be able to see, so this in itself is not a definitve test, but in such a x'over I think it is less likely that there would be caps and inductors in parallel, but this is something to bear in mind.
When doing this check on any caps, by reversing the meter connections over, each time you re-connect them you are charging the cap up briefly with the opposite polarity, but if there is no charging up happening at all (i.e no movement of the meter needle under any circumstances), then the cap is most likely broken internally.
For the resistors and the coils, you should see some steady readings which make sense and will be similar for both crossovers, except where a problem lies. Without knowing any more about the circuit layout, this is about as far as I think we should go for now. The coils should only show a fraction of an Ohm (probably less than 0.5 at a guess), but they should show continuity, of course, i.e. a definite and steady low-value reading.
Some components will almost certainly be in parallel with each other and the drive units, and this will affect some readings and if nothing obvious shows up with what I have suggested so far, it may be necessary, as the next step, to unsolder at least one end of certain components so that they can be measured individually, but let us first see what happens with the above suggestions.
Fortunately, with any stereo system where only one channel is bad, you have a good 'reference' to make comparisons with. Also, if the worst came to the worst, and you are still prepared to spend the time to save paying someone else to do this diagnositic work, you could systematically swap each component over (one at a time) from the bad to the good x'over or vice versa. This way, you are bound to discover which is the problem component, although this will be a 'last ditch' attempt, and I hope that we can discover the problem with a lot less involvement.
Regards,