Labor Day weekend, a midnite sawzall team got the catalyst off the 2014 F650 box truck: said truck has the V10 and an automatic, was a former leasing company rig. Box is nice with plenty of floor framing and the forklift can drive inside. New cat was installed by diesel truck repair shop with a butt weld to existing muffler pipe and a new flange came with the cat to connect it right after the wye, just after the trans crossmember. Aside: truck is kept in fenced yard well lit the area under the truck was fece'd (as we back it up before we steer away), cameras noted a hooded human (or alien/robot?) but not able to discern any other details, yes they cut the chain link fence to crawl through. Saw fresh red paint at the cuts, was it a Diablo blade from HD?? Police report was filed. Me decided to add a checker plate U shaped bent (like an inverted saddle) to preclude access to the catalyst. Item will go from (truck viewed lengthwise) trans crossmember to the muffler - about 42". Legs of bent are about 12". Will add Gr 60 rebar, a couple old lathe tools, and other sawzall slowing elements to the [hidden] inside of the bent, also thinking draping some short pieces of grade 100 chain to the ends of the cat where the factory has a 1/2" steel rod for the hangar isolator....the latter idea to preclude sliding the cat out of the bent as we have some photos of folks who made a 'cat cage' and then to their chagrin Team Sawzall cut off the muffler and subsequently slid the cat out of the cage.... Basically hoping this contrivance pauses em and they give up before they start stealing. The Question is: before welding, disconnect the positive from the battery and make sure the welder ground is close by and good electrical contact, sand the paint etc? The welds planned are: tacking the draped chains by way of one link to the catalyst hangar rod mounts, a piece of flat bar to the cross member to act as a flange, and then once the cat guard 'bent' is bolted on, seal welding the bolts along one flat and tying the draped chain link through a planned rat hole to the bent itself. Certainly no welds to the frame etc. PS as to the operational heat, will cut a rectangle out of the side of the bent and reinstall it by boxing it in on two of the four sides to allow air but no tool access nor any visual snooping. Indeed they could easily cut the header pipes at the engine location up to and just leave the wye and try to pull it out - this the reason for the gr 100 chains. This battery disconnection idea - anything else? Not inclined to adversely affect electrical items.
I always unhook the battery on newer stuff but i have never heared of a problem. If you are unhooking a battery always unhook the negative cable first. If you are replacing the converter with a after market one just make a sign saying this truck has a after market cat if they can read they will not cut it off. Aftermarkets dont bring much.
Take off both battery cables to be sure nothing will get fried.
Only time I personally have seen a issue was welding on a refer trailer, it messed up the [what's called the mother board] that controls engine/compressor operation. But it was on a early Carrier unit.
Only time I fried anything was when I welded on a machine with the engine running. The alternator gave up the ghost. As a side note scrap yards here are now required to get proper ID from sellers and cat thefts have all but been eliminated.
Caterpillar says 'disconnect the neg cable (switch off the master switch), and connect welder ground as close as possible." Avoid a ground path thru joints like cylinder pins or steering components. I never saw any manufacturer call for more precaution.
I am pretty sure Detroit Diesel called for disconnecting the ECM connectors so the ECM was not connected to anything. This was in the 1990s but I did find the ECM and disconnect it so that I could not be blamed if anything went wrong.
Cummins calls for disconnecting the ecm, as per Quickserve. A person is more likely to mess something up by disconnecting the ECM vs not. Don’t think I’ve ever witnessed a ECM damaged by welding. Back in the 90’s, it was a big concern. Much like quicksand, being a child of the 70’s. Watching Gilligan's Island, Get Smart, Bay Watch. I thought quicksand was going to be a much bigger problem for me.
Thank you all for the assist. Will add a couple pics (as work proceeds).
I severely melted a VHF 2-way radio mounted to the dash in my '82 truck by welding on the trailer hitch, even melted the coax going up to the magnetic antenna on the roof. I never did figure out the current path on that one. My cousin owns a custom exhaust business, he never disconnects anything, just hooks the ground on the exhaust pipe between the engine and where he is welding.
I've ruined the temper in several vice grips springs and there shouldn't have been current flow, DC welder, clean ground etc. That's why I disconnect the ground and place it on the positive so it's grounding out whatever of the wiring harness was live, basically just the alternator. The only thing I ever burned out was alternator diodes, but that was a backhoe bucket, with the ground on the bucket. Can't remember if the battery was connected or not.
When I had welding done on the frame on my 06 f250 I had him unhook the batteries, he said he never does that and has no problems. I told him I'm sure there wouldn't be a problem but having the pickup down and getting parts would suck. He unhooked the batteries for me.
No vise grips used for welding in our shop ever seemed to have a spring in them, that's for sure.