Divide and conquer.
Connect your meter to the input to the new section. Start cutting a rail.
In the future when extending or building a railroad layout, connect the meter and as you lay track any short will be indicated.
Over the years in different forums a few have built and wired a layout and first time they tried to run a loco, short.
Radio Shack use to sell a buzzer and with a nine volt battery could be used to monitor track laying. As soon as a short occur you would know.
Some digital multi meters have an audible short sound on the resistance scale.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Something is connecting the two rails together in the new section causing the internal circuit breaker on your transformer to pop. Check to see if anything metal is touching both rail. Possible items could be: track bumpers at end of track, coupler height gauge, old piece of wire, or the rails themselves touching.
Sounds like you have a short in the new section. Do you have a meter? If so check for continuity between right and left rails of the new section.
I have the right to remain silent. By posting here I have given up that right and accept that anything I say can and will be used as evidence to critique me.
I have an ho scale shelf layout using dc and manual switches. I just added a 3 track yard extension to the layout, no additional wiring involved. The track used is the old steel rail with fiber ties flex track and 2 atlas manual brass switches.
With the engine on the old part of the layout i turned the power on and nothing happens so i figured theres something to do with the extension.So i islotated the extension by cutting gaps in the rails on the extension lead ok turn the power on the old section works fine. So using an alligator clip i made a jumper to bridge the right rail gap. Powered up old section works fine. Did the same to the left eail every thing is fine bridge both gaps nothing works any clue what is wrong?