Simple battery snap to DC jack, why doesn't it work? Vintage Phase 90

[Toy Sun]

I wanted to add AC adapter capability to my 70's Phase 90 without modifying it. Plan was simple: make this battery snap to DC jack cable, take an extra bottomplate and route a little hole to pass the wire out. So I can restore it to original vintage.
Tested the wiring, it's all correct (center pin is negative) but when I connected it to my pedal chain and multi-out PSU, the PSU leds shut off and no power.
Panic that I blew my Phase 90! (why would they need polarity protection in the era of batteries?) but luckily no issue.
Now scared to move forward with this. Obviously some kind of polarity/grounding issue, but what?
Maybe not worth it to do this, but I also fear a battery leak trashing my vintage pedal. Maybe I should just sell it 

[Mark Hammer]

1)  IMHO, adding a 2.1mm power jack to a 70's Phase 90 does not decrease its value.  If anything, being able to simply stick it on one's pedalboard without having to go through all sorts of nonsense with adaptors makes it a MORE desirable pedal, not less.

2) ALL pedals, old and new, that plan around use of a 9V battery, will use a stereo input jack.  Inserting a mono plug into that jack will be used to connect the black lead from the battery to ground, thus enabling battery power.  If you are going directly from an external power source to the battery, without connecting the battery to the V+ connection on the board, and ground, via the input jack, your circuit board will not be getting power.

3) If you do decide to install a 2.1mm external power jack, the required hole will be about the same diameter as the collar of the stompswitch,   Make sure you measure the optimal location precisely, and take the circuit-board, and control out of the enclosure, when drilling, to make sure you don't get any metal shards in where they don't belong.

[Toy Sun]

Doh! The input jack for power switching. Didn't think of that (which is embarrassing, because I'm old - how old? I have the original Anderton book that I bought when I was 12).

Thanks Mark!

[Mark Hammer]

No worries.  It's nearly ALWAYS something simple.

[Toy Sun]

I gotta say, I'm proud of a few totally reversible mods I've done, not only to vintage pedals but others where I wanted to possibly resell them. This little extra backplate thing is the secret...