Pronterface bed target temp spike

I have a v0.1 reprap pcb heat bed, and melzi 2.0 electronics. I've unplugged everything except for the bed for testing (everything else works.) Temperature is being properly detected, but when I use pronterface to send a command to heat the bed, the target temp will go up to wherever it's supposed to be, stay there at most a few seconds, and then drop right back down to 0. I have two ideas, one that my ground connection is bad in which case i'd have to solder it because my crimp housing broke (i'm hoping it's this.) And my other idea is that there's some firmware problem in which case I know very little about firmware. Is it possible that a bad ground could lead to a spike in the target temp? (sorry this post doesn't have any pictures and has little detail, I'm posting this at 2 am.)

Okay, so here are some images to make things clearer.


This shows how the target temp in pronterface spikes up and then goes right down.


The bedtemp is sensing properly, it changes when i put my finger on it or take it away


The bed end terminals. the wires that (are supposed to) carry the heat are the copper ones in the blue terminal, the 2 black wires are for the thermistor, and the yellow/white wire is ground


All the connections that deal with the bed; main power, bed power, bed temp, and ground


better picture of the ground, before i soldered it

I didn't have access to any crimpers or crimp housings, so i soldered the pins. i took care to leave them isolated of each other. there is no overlap of solder and in the near future i plan to protect them with hst

I hope this is enough information. If you need more just ask. Thanks.