Rick
Is the control unit you modified from your 76 280? I looked in one from a junk 500SEL I have and it is a different number and has no resistors with the color code you mention. I was looking through Alldata and found that the wiring diagrams for the 82 and 93 S cars don't use a control unit, only a switch and 2 heaters per seat. 82 is as far back as I can go. It looks like with switches from a 82 or 83 and some wiring changes we can have manual heated seats as some others mentioned. This would suit me. Can you or anyone shed some light on this?

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84 500 SEL (307,xxx miles)