Sun, 3 Aug 2008 22:12:21 -0800, "SteveB" toquerville@zionvistas
wrote:

My SIL is a good guy and treats my daughter good. He can't back a trailer
for crap, though. He put two nice dings in my truck so far, and I've had to
repair two trailers.

He comes to me with his Yukon Denali. It has a small 4" x 4" plate where
the plug plugs in that has somehow (?) been ripped off the bumper right
along the original MIG welds.

No problem, sez I. Sez he, "Aren't you going to disconnect the battery so
it doesn't foul up the computer?" I really don't think it's going to put
any electricity into the system, and it's not welding near any computer type
component, so I sez no. But, I tell him I'll check with the pros.

I've heard to disconnect the battery, and not to disconnect. When is it (is
it) appropriate to disconnect?

Steve

I've done it both ways, main thing is to ground to what you're
welding, if you're welding exhaust ground to the exhaust. If you're
welding on the bumper ground to the bumper. If you're welding on the
exhaust and you ground to the frame, you never know what's rusty and
what path the current will take. If a nice path by way of the o2
sensor through the ECM and back to the frame is the way the current
travels then you just smoked the ECM.

Wire brush or grind a clean spot for the ground clamp.

Last car I welded on (mine) had an air bag, I disconnected the
battery and shorted the battery cables together. I don't know if this
was the best thing to do but I wanted no chance of the air bag circuit
to get power.

Anyone shows up or calls me to weld on a car I send them to a body
shop.

Thank You,
Randy

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