Welding on automobiles

[Riverrat]

I have decided to purchase a MIG welder to make sheet metal repairs to a truck I recently bought.
My question is this...are there any special precautions I should take before starting this type of job? All of the time I see folks talking about making sheet metal repairs to their cars and never hear anything about the possibility of damage to the automotive electrical systems. It seems to me that there could be some problems with connecting an outside electrical source to my trucks chassis. The truck is a 91, so it has a few computer controled items...sensors etc. I have no problems tackling a project such as this, just want to do it right.

Thanks!

[Franz]

ALWAYS disconnect the battery before welding on any vehicle.
Proper safety procedure is to disconnect the grounded side of the battery, in this case negative side.
You should also ground the welder as close as possible to the weld being made.

[flashburner1]

I agree with Franz (although I don't always do it - for shame because I know better - it is the correct procedure). Our fork trucks at work have warning labels on them stating that no welding should be performed until the battery has been disconnected. I always ground right next to my weld zone - electricity takes the path of least resistance, and I have never had to weld in the path of the electrical components of a vehicle, or had anything fry because of welding on a vehicle. I have heard of problems though! Better to be safe than sorry - you never know if everything is still well insulated on a vehicle over 12 years old - you don't want to have to replace a part because you didn't take two minutes to disconnect the negative battery cable.

[Sberry]

I ground next to the work too. I never disconect the battery,,, never had a problem. I have heard of them though. I can see with so many grounds in harnesses of newer cars it could be of concern. I asked the engineer about it and he couldnt see any real reason to disconnect. I think you could have just as much a chance of setting up an alternate ground path in the wiring system either way.

[Scott V]

I decided to leave every thing hooked,only because of a possible reverse bias going on?

[Bob]

Most electrical actuators and sensors are pretty tough and should survive minor transients. The computers are more delicate, but disconnecting them is a pain and they can suffer ESD (electro static discharge) damage from static while disconnected.
About 95-97 most car makers put a whole lot more stuff under electronic control. Pre '94 most only did basic timing and mixture control.

IMHO the most important is to have the ground connected to the same piece of metal you are welding on. The rest is probably over kill.

Bob

[Riverrat]

Thanks to all of you for the input. This should help me get started in the right direction. I have some sheet metal to replace in the back of the truck near the gas tank. Seems to me common sense would say take the gas tank off of the truck before doing any welding too. Anyone have secret for draining fuel lines to prevent gasoline fumes from possibly firing up?

Thanks!

[Sberry]

You can do that however you like. The biggest danger is hitting a vapor line directly with a torch. Most of them are in the frame. I also dont remove tanks for work on vehicles if they are not leaking. Thousands of cars are worked on every day in body shops without removing tanks. Probably more danger removing and having it sitting around than working near it. If you do remove more than likely do yourself a favor and install new tank as they rust under the straps and removal loosens it. You can sheild so sparks dont blow directly on tanks and lines. Grinding is the most notorious of fire hazzards that I have found. To plug off lines I use fuel line with a bolt in the end.