Expert: Roland Finston - 11/29/2005

Question
Where do I start to troubleshoot the drivers side heated seat in a 1999 300m.  Light comes on on switch...nothing to the seat.

Answer
Hi Jay,
This is the first time that system has been questionned.
I have to admit that I have no manuals or wiring diagrams that show the specific of the heated seats. With that in mind my inclination would be to see if any fuses in the fuse block under the dash might be labelled as being assigned to that function and if so verify the fuse and then verify that it is being powered when the ignition switch is in the run position using a voltmeter or neon glow light. If it wasn't being powered then there has to be another fuse in the power distribution center under the hood that feeds power to the fuse under the dash. I would then look under the seat for the various wire connectors for the motion motors and see if you can find a pair of wire that might be routed to the upholstered part of the seat and if so check the connectors for those wires and the wires themselves. Then I'd disconnect the plug and using an ohmmeter verify that there is electrical continuity between the two wires that go to the cushions. If there was continuity to the cushion and power to the fuse then I would check the control switch for proper function and try to verify the continuity of the colored wires that appear to connect the control switch to the seat cushions. It would be helpful to have the wiring diagram for the system. You can subscribe to a service that gives you access to diagrams called alldata.com
Sorry to not be more specific, but that is the best I can offer without a copy of the diagram for the heated seat.
Roland