Is there any trick to make soldering to corroded wires possible?

The LED tail light on my boat trailer died, but I was able to salvage some really cool red and white LED's that would be cool for a project, but since it had been in salt water the copper wires are lightly corroded from end to end and solder just won't stick, no matter how much flux or heat I use. New wires are the best solution, but the PCB's are potted for water resistance so that's going to be a bit of an ordeal. Here are some pictures:

 

Use an abrasive (like sandpaper) to remove as much of the corrosion as you can. Tin before attempting to solder.

 

Try cleaning them with a paste of vinegar and salt. Wash fully to remove the vinegar.

 

You could try acid flux, such as used for soldering copper pipes, but be sure and clean the joint well after soldering.

 

You probably have good wire up the pigtail. Cut off about 1/2" and strip and see if the wire is better looking. Do NOT use acid flux. It will wick up the wires under the insulation and slowly eat the copper away.

Paste flux (RMA - Rosin Mildly Active) should eventually allow you to solder. At worst, try RA (Rosin Active) flux.

 

Fan them out flat and scrape lightly with razor. Flip over and repeat. Rinse with alcohol and they should be shiny and bright, ready to solder.

 

I fan them out and scrape them, both sides, then fan them out in a different direction and scrape them...lather, rinse, repeat. You can get about 90% of the crud off and accomplish a solder joint. No promises on doing it again next year!

 

Soak them in Lime Away, rinse with water and a little baking soda. Worked great on my golf cart battery cables.

 

Baking soda is a neutralizer, but it's still a salt. Obsessive rinsing is a must with all chemical methods used to attack this problem.

 

Use an abrasive (like sandpaper) to remove as much of the corrosion as you can. Tin before attempting to solder.

Too much damage to stranded wire using abrasives!

A flux intended for soldering stainless steel might be strong enough.

Try a plumbers yard, and buy the most aggressive flux they have.

Such fluxes are usually water soluble, so cleaning afterwards should be easy - if its left on there, it'll wick up the insulation and corrode through the wires.

 

Too much damage to stranded wire using abrasives!

They don't sell fine grit sandpaper in your area?

 

They don't sell fine grit sandpaper in your area?

Fine enough to put a mirror finish on paintwork.

Any kind of abrasive sufficient to make the wire solderable will reduce its current carrying capacity and compromise its mechanical strength.

Finding a flux strong enough is the least bad option.

Personally, I'd just replace the wire - but if its in a car wiring loom, you just have to work with what you've got.

 

Any kind of abrasive sufficient to make the wire solderable will reduce its current carrying capacity and compromise its mechanical strength.

Don't think current capacity will be reduced much if done with reasonable care. It's for an LED taillight.

 

Don't think current capacity will be reduced much if done with reasonable care. It's for an LED taillight.

Right. That looks like 14 ga. or 16 ga. wire, good for 12 to 15 amps. No way is an LED tail light going to be pushing those limits. Probably needs less than 1 amp.

 

why not simply replace wires with new ones?

 

why not simply replace wires with new ones?

New wires are the best solution, but the PCB's are potted for water resistance so that's going to be a bit of an ordeal.

 

Right. That looks like 14 ga. or 16 ga. wire, good for 12 to 15 amps. No way is an LED tail light going to be pushing those limits. Probably needs less than 1 amp.

Then there's the compromised mechanical strength - the corrosion will have made a start on that before you start abrading metal off it.

Every time I've encountered corroded wires, I've found them more brittle than clean stock, adding to the damage is just asking for it!!! The manufacturer didn't make the wires that thick because they like giving copper away - it has to be robust enough to survive vibration.

As I said in an earlier post: strong flux is the least bad option.