Headlight relays, soldering question

SJ syljay at optonline.net
Wed Apr 20 11:03:30 EDT 2005

Use rosin flux cored, 60/40 solder. The kind made for electronic

I also use external soldering flux paste. The flux must be non acid based.
Dont use the stuff meant for plumbing. It will solder great, and then start
corroding. Soldering flux is usuall labeled as RA(Rosin, Activated) or
RMA(Rosin, Mildly Activated). RA flux is considered pretty potent, and needs
to be removed after soldering to prevent corrosion late on. Cleaning with
alchohol after soldering will remove the flux. If you cannot solder using
RMA flux, then you have corroded or contaminated  parts to begin with.

Proper soldering is part science and part art.
For the science part, you need proper tools, solderable parts, and proper
For the art part, you need a lot of practice to get the hand eye
coordination necessary for good soldering. You also need to recognize a
problem when you see one. And know what to do when you have a problem.
Most solder joints, like on a circuit board, are in 2 seconds. If its taking
longer, you have a problem.
Solder joints on 12 ga wire connections will take longer because of the
greater wire mass involved and longer time required to get the joint hot
enough to melt solder. I would think 5 seconds should be more than enough

The most common mistakes made by soldering neophytes is using the wrong
soldering iron/gun or tip.
Soldering is all about heat management.
Heat management is all about using the right iron or gun with the correct
soldering tip. Most make the fatal error of using too small a tip, and hence
a tip with not enough thermal mass. As soon as the tip touches the work, all
the heat is transferred from the tip to the work. The tip temperature drops.
There was not enough thermal mass to get enough heat to the joint to melt
solder properly. But the tip is too small to conduct heat faster than it is
being lost.

Keeping an iron on the joint longer than the 2 to 5 seconds is counter
productive. You are now just oxydizing the parts and guaranteeing that the
parts wont solder.

You are soldering 12 ga wire. Thats a pretty massive connection. You need a
large enough soldering iron and big soldering tip for that.  Or, a gun with
a larger tip that will provide a lot of heat fast.
A 35 watt soldering iron with a 3/16 tip will work. Or a 100 watt soldering
gun will work.

The old saying about getting the joint up to temperature first and then
applying the solder is pure BS. You will never get a solder joint that way.
You will never get enough heat transfer using a single tiny point of contact
between soldering tip and the joint.
What you need is a "heat bridge" to transfer a lot of heat fast.
Clean the soldering tip by brushing against moist sponge
Touch tip to joint and at same time apply some solder to the tip . .that
drop of solder is your "heat bridge"
When you see that drop of solder start wicking, insert more solder to
complete the joint.

Did I mention that this takes good hand/eye coordination and lots of

Because soldering is art and science, you will be much better off using
crimped connections. Not any kind of crimped connection . . .you need a
special tool that guarantees a  properly made crimped connection every time.
Get a good ratchetting crimping tool. The tool will not release until you
have applied enough force to make a good connection.

You are using stranded wire, right?

I have decades of industrial soldering experience, but I use crimped
connections around the car >> Faster, cleaner, simpler, more reliable.

85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q

> From: TWFAUST at aol.com
> Subject: Headlight relays, soldering question
> I am assembling a relay system for my Audi headlights and am having some
> trouble. The wiring is a combination of 12 and 14. Not being a fan of
> connectors I am trying to solder the wiring splices. Trouble is, I can't
> anywhere. I heat the wires until the "legs" on my gun get red, but I can't
get the
> solder to flow. Is there a special tip for wires this size? What solder
should I
> be using? Or is this why they invented "solderless connectors"?
> Tom Faust

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