DEC ASR-33 "reader run" debugging

Hi all -- Finally have the time (and space) to work on my PDP-8/L and its associated ASR-33. The 8/L I've had running for a while now, but I've only recently taken the time to go over the ASR-33 it came with. It was a bit dirty but it's cleaned up nicely and I've got it humming along nicely now. (With the exception of the paper tape punch, which is going to need a bit more work.) At any rate -- this ASR-33 was outfitted with the DEC "reader run" modification, and it does not appear to be functioning -- with the teletype in "Line" mode, the reader switch set to "Start," and with the 8/L running the RIM loader the reader does nothing. (It also does nothing when set to "Start" in "Local" mode, but I'm unsure if that's expected or not...) With the cover off, if I manually toggle the "trip coil" at the rear of the unit the reader runs and the 8/L receives data (and it looks to be correct). I've verified continuity between the RELAY+ and RELAY- lines measuring 15V between the two. It's about here where my naivete around analog electronics starts kicking in and I'm unsure where to go from this point -- any suggestions are much appreciated. Thanks, Josh