Help me solder my flasher
 

So my turn signals only work intermittently when I wiggle the plug going into the flasher CPU. I figured its from bad solder joints on the board. I took the CPU apart and got a look inside and took a pic. I have boxed areas of concern on the pic below.

https://irocu20.tripod.com/sitebuild.../flasher-1.jpg

So anyway the red box shows where the plug pins come through to the back side. It looks to me like the two pins with the blue boxes around them might have very fine cracks in the solder, it just looks like a little thin line. Are those the pins that normally have problems? How exactly do I go about soldering them? Do I use the tip of the gun to heat the tip of the pin and then melt the solder on the pin itself or do I heat the solder on the gun and flow it down onto the pins and board? I just don't want to damage the board. What kind of solder do I use? Its been a while since I soldered anything. One more area of concern, inside the yellow boxes in the pic there are areas that look like black/brown corrosion around the solder on the board itself. Is this anything to be concerned about? I have seen blower motor resistors on different cars with similar looking corrosion that have gone bad. I'm 95% sure the problem is just at the pins because like I said it works if you wiggle the plug but I have never heard the overrev buzzer go off (tach doesn't work 100% though so I might not have reved it high enough yet) so I want to make sure there aren't two problems. Thanks for the help everyone.

Yes, most of those pins in the red box had cold solder joints which caused the same problems for me. I resoldered all of them. I inspected the others and they all looked fine.

Inside the yellow boxes is flux that wasn't cleaned off. Use some 99% alcohol and a tooth brush.

Ah, the wonders of soldering. I'll tell you what I would do and electronic engineering is my field of work.

Yellow boxes appear to be old flux used in the initial manufacturing process. Some isopropyl alcohol will take that off. Use a small brush or something like that.

If you want to rework what is in the red box, do the following:
Buy a 15-30W iron such as this: http://www.chipworld.co.uk/store/ima...ering_iron.jpg

Buy some LEADED solder. Your board has leaded solder so trying rework with lead free solder is a pain.

Heat up the iron and apply a small dab of solder to the iron. Not too much just a touch like the head of a couple pins.

Place the iron on the solder joint, roughly next to the outline of the pin. You are trying to heat up both the pin and the pad on the circuit board. Since there is already solder, let the existing solder melt and keep the tip touching the pin and the molten solder. Add more solder if needed.

Cool, thanks for the info guys. As far as the solder, are there different types of leaded solder or is there only one kind?

The best is eutectic solder, or 63/37 solder. You also want fine solder, not huge plumbing solder.

https://irocu20.tripod.com/sitebuild...ures/fixed.jpg

Well I soldered the four outside posts and one more on the top row left of center and I think thats all the connections what were questionable. Hopefully this will work.

Not bad. The larger pads don't seem to have been fully heated but that's hard as they act like a heatsink. Try it and see if it works.

Remove that black flux residue as the older stuff if not cleaned will eat away at the solder traces.