I think I know what the TS is up to. He may have plans to make the rear amber lights go on with the park lights using the 5W filament of a dual-contact bulb. The signal lights are then connected to the 21W or 25W filament of the same bulb so that the amber lights still functions as turn signals.
To the TS, I'd leave it stock if I were you. It's not that I question your intentions, but more for standards compliance. Having turn signals that are constantly on is not only non-standard, but can cause confusion to drivers behind. As per international signaling standards, only red light should be seen from the rear of any vehicle that can be constantly on (aside from license plate illumination). Constant-on amber lights are used on oversized vehicles as marker lights on the side (long vehicle) or top-front corners (tall vehicles).
Furthermore, and without offense, the practice of doing the said DIY is so 1980's.
