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Re: Aftermarket Seat Heater Wiring and WTH is this?
What are the pads rated to draw at max? If it's low enough, and the wiring is sufficient for the current, you could tie them all together and run them to an add-a-fuse with the appropriate fuse in it, on a switched location in the fuse box. For reference, if the wires are 16ga, the total power feeding capacity will be about 3.5a. Move up to 14ga, and the capacity grows to about 5.5a. I highly doubt the wiring is bigger than 14, but maybe. If it's 12ga, you could run a load of 9a safely. The grounding capacity of these is far higher, so no need to worry over that side.
If you tied them together with bigger gauge wire capable of carrying the full load for all four heaters, as long as the existing harness off the heaters is sufficient to carry the load for one heater, you could put them all on a single circuit. Just be sure you use good connections and isolate them well. Heaters are resistive and will draw a fair amount of power and generate a good bit of heat (duh! Heaters generate heat...) so wiring is a key here.
A quick check of the eBay seat heaters shows them all ranging from 4-5a draw, based on a 12v circuit, per seat (2-2.5a per pad). So you will need at least 12ga wire to tie them all together, and 10a would be better to avoid potential electrical fires. Each pad would only need 16ga wiring from the tie-in to the individual pad. Now, if your pads are rated for something other than 48-60w per pair, the equation changes.
Last edited by dubyam; 03-20-2017 at 10:12 AM.