Lionel SW7 ground issue with MTH Track

Connect the outside rails together. Atlas track is the same. It's not that way for 2 rail operation; it's just the way it is.

I wonder if maybe take two of the traction tires off. It would probably still get good traction and it might give it better ground.

Can almost guarantee that the left side of the engine and the right side are not insulated from each other, so if the train is on the track, your rails are connected.

I found scaletrax to be a bit fiddly. Would suggest going down the rails in the spots where the engine has issues with a multimeter and making sure you have power on the tracks when you measure from the center to one outer rail and also to the other.  You can solder a jumper between the outer rails somewhere too, that would help.   You cant run 2 rail locos over 3 rail switches without doing some electrical work to them anyways, so you're not losing anything by adding a few jumpers. I have also encountered some scaletrax switches with a cold solder joint that would kill anything when a roller hit the rail joint... thats obvious because it sparks on the roller.

Thank you all. I think I have to investigate more. I will check every section with a meter. I’ll check the traction tire heights also.

Where should I place the outside rail jumpers? Should I do it at every drop?  Should  I do all three sides of every switch?  The switcher works fine on some sections and later poorly  on the same exact section. It’s very hard to isolate where the problem is. Hopefully checking with meters, going center rail to both outer rails one at a time will teach me a little bit more. What is an easy way to do this? Do I have to wreck many areas on my layout just to make this one loco preform? All track has ballast and is over cork. Does anyone have an easy method for placing the jumpers.  All my other locos, legacy included, work just fine. Thanks for the help.

I wouldnt destroy yet.  First buzz out what you've got with a meter. I'll take a gander that some of those tabs between the track got glue in them when you ballasted and you have some iffy track to track connections.

As far as checking it, put the red wire on the center rail and the black wire from the meter on the outer rail. I would also check with from the center rail on 1 piece of track to the outer rails on the adjacent pieces of track. That will enable you to figure out where you have a bad connection.  You did say everything else runs fine, so I would do this for a little bit and then explore elsewhere if you dont find an issue.

The loco could be rocking on the traction tires and losing contact with the rails. If you have MTH traction tires, that seems to be a standard replacement for terrible, thick lionel ones. Also put the meter in OHM mode and verify that the trucks are actually connected to each other (touch wheels from one truck and the other truck with the wires). Do the same thing with the pickup rollers on both trucks.  Its possible theres a bad connection in the engine too.

The jumpers dont need to be big wires. On the inside of the rail, drill a hole through the table, drop a wire and solder it to the base of the rail. You can either loop it back up through the table to the other rail, or use another short stub of wire and make a 3rd solder connection under the table between both wires. A few drops will do you.  If you only have 1 drop from the transformer, a switch might be interrupting the path of the ground. Generally you would want an electrical drop between switches. The switches are typically jumper barred underneath to pass electricity through both paths of the switch, but maybe one of them isnt connected.

To test just use two alligator clips to connect both outer rails .

Thanks everyone.  It’s my nature to try the easiest things first and hope they work. I decided to throw parts at this and picked up some MTH traction tires off eBay because  that would be the cheapest and easiest fix. I never got around to metering the track I was  very busy and distracted by other things. However with the new traction tires the loco  does run fine it’s made it through all my loops and switches  perfectly. It must have been losing ground rocking on the Lionel traction tires. Now that the loco runs fine I have a follow up question. The mth traction tire part # was DE-18  which states it fits all MTH diesel’s. However they are a little larger in circumference compared to the Lionel traction tires and do not grab the wheel tightly they just fit loosely. Does anybody know of another tire that would fit the wheel better and still be thin like an MTH tire.  The Lionel tires just are too thick to work. Thank you for any help.