I have an '80 DeVille which has a six-way power seat which only functions in the rearward positions--(it goes back, it raises and it tilts backward)--it will not go forward, lower or tilt forward. I do hear clicking at the motor when I attempt one of these forward positions, so power appears to be getting to it. I suspected the motor, transmission and relay located under the seat, so I changed them all--(3 times) but I still have the same problem. Is there another separate rely located elsewhere that controls the forward positions or could this problem be related to something else? The service manual does not provide sufficient detail on troubleshooting the system to help isolate this problem.

 

The functions that you mentioned go from the switches to the power seat transmission module. The module dictates rear height, front height and FWD/Back. If Fwd/Bk is one of the issues then you want to check the light blue wire for voltage.Rear height is the yellow wire and front height is the green wire.Have you had the front driver door panel off at any time. The multi connector in there could be loose too.Spray some WD40 in the switches to combat any rust issues or if you spot any green oxidation on the switches.Ground must be good if you have some seat function.As a side note there are three control solenoids inside the transmission that operate the clutches for various functions. Other than that check for continuity at switch during various postions.

 

Thanks very much for your response. In order to effectively test the motor and transmission, I separated them and then actuated the switch functions. Clicking at the transmission occurs at all functions, however when the motor is connected to the blue & white wire connector, only the backward functions cause the motor to spin. At this point, I suspect the relay is not reversing polarity as would be necessary to cause the motor to spin forward. However, since I have changed out this relay three times with the same results, this seems to be odd. Could there be another hidden relay somewhere that enables the motor to revserse its polarity?
Any additional thoughts or feedback would be greatly appreciated.

 

In the schematics there doesn't seem to be any other relays in the circuit. I'd be leaning towards the main switch. The relay can't always be the weak point.Must be some thing triggering the failure.

 

Try taking the power seat transmission out and cleaning and lubricating it. The white lithium grease dries up over the years and this will make a balky transmission work like new. It's not difficult but you have to be willing to wrestle the tranny out and tear it apart. It is cleverly designed and intuitive to work on. Obviously you need to buy some white grease.