I personally wired my Scheel-Mann seat heater elements directly into the OEM seat heater circuit. I did it the same way as Toyota - elements are in parallel (12v) when on high and series (6v) on low.
The OEM circuit is rated for 20A and also includes the rear heat. Since my rear heat is disconnected, I swapped the 20A fuse for a 15A fuse and haven't had any issue with blowing fuses with both seats on High for several hours. The seat heaters may be capable of 15A per seat but I'm certainly not seeing that in practice...
Yes, I thought about doing that too. However, I have to check under the gear shift console if the LX comes with the front seat heater harness. After researching, it looks like most 80 series and a few LX450 came with the front heater harness. Not mine though, only the troubled rear heater was installed.
On the Lexus side, according to the depths of the internet the ones that came to the US had the front seats heater installed through the dealership. Someone correct me here if I’m wrong.
If mine has the harness for the front heater, I’ll definitely use it. The Sheel-Mann runs 15A per seat and their relay can run up to 40A. Knowing that the OEM circuit runs 20A helps a lot. Thanks for that info.