Guitar pickup level inputs to most amps are designed to handle a 1 volt RMS signal more or less. If you were to read 1 volt in your test it would be about what I would expect. However quieter pickups will be in the 0.1 volt range.
When you said your tuner works, I would suspect the wiring from the preamp to the output jack, or the output jack itself. If you are up to it, you can see if removing that connection (I don't know if it is screw contacts or plugs) cleaning the ends with contact cleaner by spraying a cotton q-tip and using the q-tip to wipe the contacts (DeOxit is the name brand but the stuff at Home Depot is fine as long as you don't use it for Pots which are not metal-metal contacts).
Last edited by jonfields45; 08-13-2017 at 06:39 AM.
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