Dimmer - 120V in, 70V out, normal?
You will never get 100% out of a dimmer, but 70 sounds low. Do you have a trueRMS multimeter or a cheapo unit? A non-RMS one could be mis-sampling the AC voltage given the irregular shape of the resulting AC waveform, which can give an off reading.
I would also check again with a load (bulb) in-place. You might not have enough current to get the triac (the component that &quot;dims&quot; AC) to latch (holding current, often &gt;10ma, aka 1.2 watts in USA) early enough in the sine wave. Adding a load will enable everything to work as designed, which could (should?) fix the issue.