How do I use this PSU/ should I?

While ripping apart an old printer I found it had a nice looking "+5V/1.5A, +12V/3.5A" power supply. I tried searching for a data sheet, but couldn't find one. Here's a picture of it (top right). It's an "open frame power supply unit " made by APD, but they don't even list my model (APD-6018-50A1).

Anyway, I tried plugging it in (careful not to get electrocuted of course) and seeing if it could run a large DC motor from the +12V, nothing happened, even when I tried it along with a 10ohm, 10Watt power resistor.

It has some additional pins and I thought some of these might need to be shorted, like the green signal wire on an ATX supply, so i tried shorting the sets of pins, and one of them made the motor jump, but then it just kept "ticking" every half second or so; go, wait,go,wait, etc.. Un-shorting and re-shorting the pins makes it jump then tick again.

Any ideas how to get it working, or should I stick with a hacked ATX PSU for my robotic power needs (automated airsoft turret)?

Either you need load on the 5V rail, or the motor is pulling too much current on startup, and the PSU is going into protection.