My MTH 2-6-6-6 Allegheny is throwing sparks between the draw bar and tender hitch

Could the draw bar on the engine be dragging on the center rail?Nick

If this is PS-2 I am not sure why it would do that, unless it has a ground issues in the engine.  Are the wheels clean, open shell and check the chassis ground wires (black).  Does this have a tether or the wireless draw bar?   G

There is no contact to the center rail.  I checked over the engine and seems ok.  I hooked up a tender from another working engine and it operated perfectly.  Both tenders have the wireless draw bar.  So it seems to be isolated to the tender.  I checked ohms from the truck wheels to the end of the plug and they are consistent with the other tender that operates ok.  I saw some articles about adding a tether but was not sure if that would help after checking the ohms. 

Something in tender is wrong.  Open tender and check wiring and how AC wiring mounts to chassis and any tender pickups on trucks.  This sounds like a possible ground issue on the AC side, or maybe a purple Positive Voltage issue grounding to chassis.   G

Hey Guys, I am having the same problem with an MTH 4-6-2 Torpedo with a tether. When hooked up to a Mallet tender the engine runs fine. I opened the original tender and found everything to be fine. When I tried to run the train with the original tender the same issues continued. I hadn't seen any ground issues.                 Any other suggestions?

You guys need to be careful just swapping tenders.  IF the engine are not the same or same configuration you do risk damaging the circuit boards.

As far as arcing you have to be specific in where it is coming from.  Truck interface is usually a chassis ground issue, and or the Positive voltage short to chassis.  So the AC wires from the truck are always suspect at the terminal or where it comes through the frame.  Broken insulation or heatshrink, causing a ground.  G

Success!!  I finally found the problem.  First off, I was almost positive the tenders were the same.  Like G says, I did not want to do further damage by swapping them out.  So anyhow, after tracing the wiring and many other parts of this tender, I finally found the cause.  There is a long bolt that secures the two circuit boards together and also to one end of the mounting bracket that holds the whole assembly in the tender.  There are four circuit board devices that I believe are diodes. (They are black and about the size of a small marshmallow.)  They surround that bolt.  Somehow, the wire from one of them got pushed in and onto the bolt was causing the short.  I'm glad it did not fry the board.  I was able to bend gently bend them back into their proper position and cure the short circuit.    I just pulled the "Star of the show" off the main line to give it a wrest after a two hour trouble free run    Thanks all for your help and suggestions.