Wat Daeng, or the Red Monastery, was located off the city island in the southern area of Ayutthaya in the Samphao Lom Sub-district. (1)
The monastery stood south of Wat Nang Krai and north of Wat Khok Khamin. Wat Tamnak was on its east.
There are no traces of the monastery above ground level, except for some broken Buddha images.
Historical data about the monastery and its construction are unknown.
The monastery is mentioned in the Royal Chronicles of Ayutthaya before the escape of Phraya Taksin (reign 1767-1782 CE) to the south.
"Then the Burmese advanced forward and established stockades in the Monastery of the Krachai Plant, the Monastery of the Victory Pavilion, the Monastery of the Stove (Tortoise), the Monastery of Gold and the Monastery of Red." [1]
Wat Deang is only shown on Fine Arts Department maps.
The site is in geographical coordinates: 14° 20' 15.03" N, 100° 33' 12.85" E.
Remark:
The 2007 CE Fine Arts Department map shows a temple with an identical name [วัดแดง(๑)] about 150 metres south of Wat Daeng. Based on the map, the site is in geographical coordinates: 14° 20' 7.98" N, 100° 33' 14.46" E. I presume it must have been a part of the same monastery.
Footnotes:
(1) Sub-district called after the village Ban Samphao Lom near the Chao Phraya River. The village is on the Monthon Krung Kao map (1916 CE). John Bowring (1857, London, John W. Parker and Son, West Strand), in his book ‘The Kingdom and People of Siam’, wrote: "Between the modern and the ancient capital, Bangkok and Ayuthia, is a village called the “Sunken Ship,” the houses being erected round a mast which towers above the surface at low water."
References:
[1] Cushman, Richard D. & Wyatt, David K. (2006). The Royal Chronicles of Ayutthaya. Bangkok: The Siam Society. p. 512.