Here’s the issue. I wired the Lionel gateman accessory with an insulated piece of track (tubular steel track). I ran the wires like I have in the past. Everything works, but when the metal wheels of the freight cars run over the insulated track section they produce pretty big sparks. I don’t recall this happening in the past when I’ve used the same technique. Any suggestions. Thanks in advance.
Make sure both the wheels and track are clean. Sparks are usually caused by poor electrical connection, and most people never think to clean the wheels of their rolling stock!
Welcome aboard pblioneltrains! 
Thank you, I’ll give it a try and respond if this solved the issue.
Yellow Tank is correct. Poor electrical contact is the cause of sparks. Start with clean wheels and clean track. Do these freight cars have middle rail pickups? Sometimes the rollers of the pickups will skid instead of roll. Make sure that they roll freely.
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Thank you. Here’s what I’ve done. I cleaned the track (although it was pretty clean to start with) and I cleaned the wheels of each car with my Dremel tool and electrical cleaner. It helped somewhat, but there are still small sparks when the cars pass over the insulated portion of track. The engine has traction tires, so no sparks with that. It doesn’t happen anywhere else on the track but that spot. I’ve doubled checked the wiring and it all seems correct. It remains a mystery.
The sparks mean you have a voltage difference across the gap in question (which you could measure with a multimeter) and this produces a short when a conductive wheel or roller momentarily bridges that gap.
A cheap kludge to solve the arcing might be to fill the insulated ‘gap’ very slightly above railhead profile with a shim or nonconductive epoxy, so there can be no bridging contact as the wheel ‘falls’ into a gap.