The A5104 is a fairly long cross-country road running from near Corwen in Merionethshire to a point on the south side of the River Dee in the city of Chester. Apart from the last 6.5 miles east of Penyffordd, the route is the same as that of the original B5104, which was upgraded to Class I status in 1935 while retaining the 5104 number.
The route starts at the point, a mile north-west of Corwen, and on the opposite side of the River Dee to the town, where the northbound A494TOTSOs left towards Ruthin. The A5104 heads north-east towards some low hills, soon crossing a saddle to enter the valley of Afon Morwynion and Denbighshire. The road follows the river upstream for the next six miles or so, sticking to the northern slopes of the valley except where it briefly crosses to the other side of the stream at Bryneglwys.
As the valley gets narrower the road climbs out to reach a roundabout where it crosses the A542. The road descends again to cross the River Alyn and reach Pen-y-stryt, where the A525 is crossed at a staggered crossroads controlled by traffic lights. The road then enters Flintshire where it skirts Moel Garegog and climbs onto the moors once more. It reaches a summit of over 1,100 feet then starts to descend gently over several miles. The B5430 is soon crossed at traffic lights at Rhydtalog, after which the road passes to the south of Treuddyn. As the road runs along a valley the speed limit drops unexpectedly to 30, despite there being no houses or lighting here. Presently we pass the unbelievable-sounding Pontybodkin and reach Pontblyddyn where we cross the A541 at a staggered crossroads. The Alyn is crossed again and the speed limit increases. We soon go under the Borderlands Line by Penyffordd station to a roundabout on the A550 Penyffordd bypass.
At one time the A5104 continued into town where there was a short multiplex along the A550. Now, however, the multiplex runs along the bypass to the next roundabout. The road to the left is the A5118 and the A5104 regains its number by turning right. The old road soon comes in from the right, after which the road bears left to cross the A55 at J36. The road skirts Broughton and reaches a roundabout where it meets the B5125. That road follows the original line of the A55 which we now take over. We pass Hawarden Airport, where there is an Airbus aircraft factory, after which there is a brief rural section before we reach the outskirts of Chester.
Initially, as we pass through Saltney, we are still in Wales but we enter England and Cheshire in time to pass Asda and go under the Chester to Shrewsbury line. The road continues along Hough Green and soon reaches a roundabout where it ends on the A483 just to the south of the city centre.