Tapa Martinthi Yala

Like most of the options you head south east from Salt Pan Junction back towards Salisbury Highway. It would seem that this path is called Tapa Martinthi Yala, at least until it crosses the highway and then it's the Northern Connector Bikeway.
Anyway beware of the sharp turn at the end of the long drag and the small bridge soon after the turn as it still doesn't have a sealed surface.
The culvert under Salisbury Highway often has a layer of slime, sometimes water too. Only the right hand tunnel actually extends under the highway.
After the culvert there is a turn to the left that will take you to South Road but go straight ahead next to the wetland.
The path will eventually turn to the right and exit to Magazine Road.

Magazine Road and Churchill Road North

Magazine Road has sharrows, it's part of the Northern Connector Path and the Gawler Greenway but I'd still be careful of the trucks. There are two railway crossings for freight trains from Port Adelaide. They are still used so keep an eye out for flashing lights! There is also a tiny piece of shared path at the end as it connects to Cormack Road but it's not really worth using, especially if your plan is to cross the railway lines.
Churchill Road North is quite wide and has been resurfaced in places. Still there are trucks.

Crossing Port Wakefield Road and Cross Keys Road

The crossing of Port Wakefield Road has a cyclist call button, which is useful on weekends when there might not be a car/truck to trigger the lights for you. If coming the other way there is a small spot for cyclists next to the button so you don't need to sit out in the middle lanes (there are two left turn lanes).
After crossing Port Wakefield Road turn left into Cross Keys Road. Cross Keys Road runs through an industrial area, potentially with Road Trains parked. It's two lanes each way and pretty quiet on weekends although I was passed by a B-Double today.
At the end, where the road itself bends to the right to become Levels Road, there is a path that will take you into Mawson Lakes.

Into Mawson Lakes

The path crosses a drainage ditch and then drops you into a suburban street. Continue straight ahead towards the park and up onto the path. Continue past the BBQ and shelter, past the lake and across Mawson Lakes Boulevard. The path is continuous even if it appears to be ending on a road. It also crosses Parkview Drive (an ugly little corner and terrible ramps) before joining the Dry Creek Trail. You can take the bridge across the creek if you wish but you want to exit on Mawson Lakes Boulevard on either side of the Dry Creek and turn right. I got stuck behind two women with a pram so went under the Mawson Lakes Boulevard bridge and exited on the other side. After going around the roundabout the cafe will be on the left.