There is a move to lead-free solder. The so called "RoHS" requirements went effective last July. There are exemptions for many industries including automotive, however not all companies use all the exemptions. The European manufacturers have been early adopters of environmental practices.

You are making 2 different points here:

1) 'When resoldering you should remove all the old solder and use new solder'.
You are absolutely correct. 100%. This is exactly what should be done. I mostly use a "Soldapult" solder sucker, but wick also works fine.

2) 'Lead solder is "better" than lead free solder'. Strictly speaking this is not correct. I have seen no claims from anyone in the industry that lead free solder is inferior to lead solder. However, it needs a higher temperature and there are several different alloys being used, so from the point of view of the DIY'er (including me) I use tin/lead 63/37 solder. This is also sometimes known as Eutectic.

As I believe I previously stated, the trouble is in the single sided PCB with no plated through holes. This type of board is cheap cra* that does not belong in a Mercedes. It doesn't belong even in a Hyundai IMHO. These boards WILL fail in industrial applications or in any application with heat cycling such as in TV sets etc.

So, remove the old solder, clean the area with a clean toothbrush, use new 63/37 lead solder.

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

I just repaired the relay in my wife's 98' C280.

To be specific about the relay location;

After you remove the carpeted truck liner, there is a large black plastic cover towards the front of the car. It is about 2 feet by 3 feet, and is held in place by three large head plastic screws, which you should be able to remove with your fingers.

Lift off that cover then locate the relay toward the right, it's easy to see and is positioned horizontally. It is the only relay that I could find under this large cover (there is another relay under a small black box, that can be accessed without removing the large black plastic cover)

Once the relay is removed, I used two knifes to pry the sides away from the relay bottom to slip off the relay cover.

I only found one, possibly two locations with cracked solder, I fixed them both of course. I didn't remove the old solder however, I simply heated up the bit that was cracked until fluid, and then added a small amount of thin resin core solder to blend in.

I realize that this isn't the way explained in other post, but I'm confident it will be adequate in this situation.

I don't know the difference between an ohm and a volt, but I want to fix my seat intermittent issue on my 98 C-class.

How much is a new relay?

Will solder and a solder gun purchased from Crutchfield years back work in repairing this relay?

I will probably just resolder on top of the original solder on the relay, any tips or mistakes to avoid to prevent a disaster?

I don't know the cost of a new relay. Hopefully someone else can chime in. Maybe 20.00? As far as the finer points of soldering that was mostly covered in previous posts in this thread, take a look. I don't know what gun/iron and solder you have. It is generally better to at least add some fresh solder (flux core). Ideally you remove the old and then resolder. It is like Sears says, "good", "better", "best".

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Just repaired my wifes 98 C230. Thanks.

__________________
John


1998 C230 for the wife
1986 Porsche 944 Turbo for me in the summer
1993 Audi 90 for me in the winter

Yes, this is very true. There is no "better" solder necessarily, as different applications call for different metallurgies.

The thing about lead-free solder that most people don't realize, and what leads to a lot of its bad rap, is the fact that it doesn't produce nice shiny solder joints like a good lead solder will.

With lead solder, the color of the solder joint is a very good indicator of how well the electrical and mechanical properties of the joint are. Lead-free solder can make a perfectly good solder joint that looks dull and "cold", and it takes a long time to mentally adjust yourself to that, leave the joint alone, and go on to the next one. People used to lead solder will tend remove the old joint and re-solder it over and over thinking that they are getting a "cold joint" or a contaminated joint. This leads to frustration and reports that the non-lead solder isn't as good.

One thing's for sure, it definately requires more heat. I try to avoid it when working on heat sensitive components for that reason.

There are MANY different lead-free solders on the market. I have most recently used the green labeled version by Kester, which uses antimony instead of lead. Not exactly a less toxic metal in my personal opinion, though the amount of antimony is low and just added to increase strength.

I agree that through-plated holes in the PCB would have likely prevented this issue. Just remember - failure in less than 5 years = money loss. Failure after that period means money gain. That calculus finds its way into manufacturing decisions, you can bet on it.

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-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition