I'm working on retrofitting '14 Lincoln MKS 14 way power heated/cooled seats into a 2002 4Runner. I have all motors & lumbar wired. Had a Eureka moment on the TED and got it working!

3 position on/off/on rocker switch - hot/off//cold to: 5 pin 30 A relay - fan motor wired direct from relay with pigtails out to 8 pin DPDT relay to control hot/cold.

Fan is +/- in either on switch position. TED is +/- left, -/+ right.

Works great!

However, no resistor, thermal control...

I tried wiring pot/var resistor to the out on DPDT to TED - only works 1 of 2 switch on positions (guessing other = -/-)

Would a dual potentiometer work? Would think it should and would wire in-between dual + out from 5 pin to dual in to DPDT. TOP /outer knob wired say +/-, bottom / inner knob wired -/+

Outer/top should only engage in say hot, inner/bottom only in cold.

Think I have it right but would love verification or simpler way if available.

  • \$\begingroup\$ If the TED is a TEC, pot probably won't work well for cooling which needs on off bursts rather than a low current. Heating mode is a lot simpler though as it's easy to make heat with either. \$\endgroup\$
    – Abel
    Jul 28, 2022 at 2:12
  • \$\begingroup\$ A simple potentiometer on a high current heater line would likely just over heat and burn out. If you were determined to do this then a high current pulse width controller might work. For the cooling fan you might use a similar pulse width controller but at a faster pulse rate. Look up pulse width speed/heater controllers for some examples. \$\endgroup\$
    – Nedd
    Jul 28, 2022 at 5:38
  • 1
    \$\begingroup\$ @Abel That is backwards. TECs do better with current limiting rather than PWM. \$\endgroup\$ Jul 28, 2022 at 18:31
  • \$\begingroup\$ Need for current limiting is not eliminated with the pulses. The theoretical and practical best for cooling with a TEC involves shutting down current while the cold thermal mass you created absorbs some heat. If you do not provide such an opportunity, the current you flow while that happens just adds heat. \$\endgroup\$
    – Abel
    Jul 29, 2022 at 0:24
  • 1
    \$\begingroup\$ With TECs, efficiency is what typically holds you back from using more power. Their inefficiency generates so much heat (that also needs to be transferred), that ends up dominating. This is one of the main things newbies struggle with when using TECs, I don't want anymore beginners to get the idea that pulsing them with bursts is a good idea. You almost always want current control, and when you don't, you better know what you are doing. \$\endgroup\$ Jul 29, 2022 at 21:54

1 Answer 1


You should buy a switching regulator PCB from ebay/amazon, and modify it so the voltage control is on your instrument panel.

Then you just feed this voltage into your forward/reverse switch.

TECs work best with a constant voltage or current, not PWM (although PWM can be used). At a higher current the TEC is less efficient, and 50% high current, 50% zero will not give you efficiency as good as 100% medium current.

Along the same vein, you should be aware that the maximum voltage does not always result in the lowest temperature when cooling, as the thermal dissipation increases with the square of the current, while the heat transfer is only proportional. After a certain voltage (which varies with the operating conditions), more voltage will actually make the cold side hotter.


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