Today: MIG Welding an Older Truck?

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Dear Car Talk

May 5, 2015 (Archives)

4 Comments

electrical wiring, DIY

Dear Car Talk:

I have an older pickup with an all-metal cab frame. There are numerous holes drilled in the dash and frame from old CB and gun rack mounts. I was told that the best way to fill these is using a MIG welder. What precautions need to be taken to protect the vehicle's electrical system when I weld the cab frame? Thanks.

-- Ray

I'm less worried about your electrical system than I am about your retinas, Ray. MIG welding is dangerously bright, and without proper eye protection, you could blind yourself. 

After that, fixing the holes in the dashboard would drop down on your priority list because (A) you'd no longer be able to see them, so they wouldn't bother you as much, and (B) you would have great difficulty securing a driver's license. 

But a MIG welder is what you want for this job. "MIG" stands for "metal inert gas." It uses a thin wire and bathes it in an inert gas to push all of the oxygen out of the way. That keeps the surrounding metal from oxidizing, and allows you to seamlessly and smoothly weld metal together.

Which electronic components you need to protect depends on how old your truck is. If it's old enough to have a metal dashboard -- from the 1950s or '60s -- then there aren't really any electrons to protect. In fact, I'm pretty sure in that case your truck would have predated the discovery of the electron itself.

Then all you have to worry about is the heat you generate. So you'll want to get under the dashboard and move away any wires that are in the vicinity of the weld. You also might take a picture of the wiring under there so that when you do melt the wires, you'll have an easier time rewiring everything. 

I also would use some sort of insulating material -- like a piece of sheet metal -- between the welding site and anything you might set fire to. Another good precaution is to do a little bit of welding, then take a look under the dashboard and make sure nothing's glowing.

To be on the safe side, I would have a fire extinguisher nearby. And I'd wear a good pair of sneakers in case you need to run for your life. 

If your truck is newer than that -- say, 1980s vintage -- then you will have some electronic equipment. In that case, you'll need to unplug and/or remove anything with a printed circuit board before you send all that electricity through the vehicle. 

All of that stuff is plug-and-play, so you should be able to just disconnect it and then reconnect it when you're done. That stuff would include the electronic ignition components, the computer, if you have one, the radio, and maybe even the instrument cluster if it's got a circuit board. 

But other than that, get the right eye protection, and try not to set your car, your house or your hair on fire, and you should be fine, Ray. Best of luck. 

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electrical wiring, DIY

• 4 comments
• Car Talk

qwildman • an hour ago

The scariest part of this question is that you admit that you used to have gun rack mounts.

capn b • 4 hours ago

if you can, get some copper scraps and form them to fit the contour of the areas you are welding. put them behind the holes before you weld, it will act as a heat sink and support the weld so it will come out nicer. and the copper won't stick to the weld. also mask all the glass. spatter and glass don't get along.

dvdlgh • 5 hours ago

When you're done you will have some painting to do. Body putty is a lot easier and will save you money and time.

johnbarry dvdlgh • 4 hours ago

And safer.