Yes, T115A handle with modified plug (with added "stanby" pin #4 and wire soldered to it) is connected directly to the host. Other end of the added wire must be connected to mast with bracket for T115A handle.
Yellow pair must be disconnected from mast's nut because this pair is "standby" pin signal of cradle's plug that also connected with T245/210 bracket and work with other channel (T245A handle in my case).
Sorry for my English, I can't explain it in any more detail or more clearly.
....
There is another way to get "donor's" pin without buying donor handle or plug. You can extract pin #3 (extractor) from plug of holder. But in this case you have to connect extractor in parallel with bracket so that the station goes into standby when you change the 245/210 tip.
But buying a donor T245 handle is more reasonable, since this handle does not lose its functionality after removing the unused pin #6 and can be useful at any time if the genuine AiXun T245A handle breaks.
Do you have a photo or diagram of how the wire to the tall stand is connected to the main station? Is that standby pin just a ground pin or something different?
Wondering if might not be possible to internally connect the standby pins of both channels inside the main station so there's no need to run an extra wire.
Does anyone else know how these soldering stations work to put irons into sleep mode?
T420 in the T245A configuration (with T245A handle included, but without specific mast with hangle bracket for T115A handle) have a regular price for $181.48 at this store. I used a $20 coupon at "anniversary sale". But similar coupones or promocodes you can get it very often. Aliexpress holds different sales almost every month.
The T115A handle i bought at the China DIYPHONE Store aslo with coins. Regular price was $8.19.
Additional cheapest T245 handle I bought for $3.03 with coins just to have a "donor's pin".
Your prices are just across the board cheaper than mine, I believe it has to do with location as they probably have shipping costs included in the total price of the device. I shopped around quite a bit to find the cheapest I could and $210 was the cheapest before any coupons.
In hindsight, the cheapest maneuver was probably buying a T405 unit and hoping to get sent one with T420D firmware and buy the 245 handle. I think this would be the most cost effective as I've seen the 405 go for $170 before coupons and it would also include the little arm stand and you wouldn't need to buy those separately. Still a gamble though because no way to know if you'll get a main unit with T420D firmware.