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Old 02-05-2007, 11:25 PM
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Power Seat Wiring Info Needed- Mid 70's Chevrolet/Chevelle

I'm rebuilding the seats in my '66 Elkie, which I acquired from another '66 Elkie in a junk yard many years ago. I once knew the actual vintage of the seats, but have forgotten the exact vintage. However, it was Chevelle or Chevrolet, I believe, for sure GM, of mid-70's origin. They
are 60/40 buckets with center console, fancy polished aluminum trim on the exterior side of the backrest and seat cushion, and fold forward, as if they had originally come from a 2-door vehicle. The rear of the seat bottom is finished in a carpet material, while the front and back are typical "bucket" vinyl of that vintage. It's obvious they originated from a more premium vehicle than my Elkie.

The problem is in the operation of the driver power seat operation. The electric motor is refusing to operate correctly, nor does it's associated relay acting quite like it I believe should. Because I don't know the vintage, I can't locate an appropriate wiring diagram.

However, I'm hoping that someone may know of the particulars of this setup as I describe it thusly: A single motor, horizontally mounted at front of seat frame, connected to a "transmission", with 3 dual-side connectors with speedometer-like cables, one for the dual front-rear direction gear motors (one on each side of frame rail), one to the pair of front up-down "gear" motors, and one to the pair of rear up-down "gear" motors. From appearance of the electrical connector on this "transmission", I suspect it contains three different solenoids that operate one of the three sets of output connectors (to the speedometer-like cables) at a time.

An appropriate "slight" clunk in the transmission tells me that it should be operating OK. When using the motor attached to the relay and seat controls (leaving the motor unattached from the "transmission"), the motor will not spin. It appears that this is a motor with separate field coil and armature circuits, with the armature lead connected to the "hot" brush, the other brush to ground; and then two leads to (perhaps?) each "half" of the field coil, which ground wire I can see on the brush end of the motor after removing the end plate. The armature turns freely, and I have continuity through the armature+brushes, as well as through each "half" of the field coil.

The relay is more mysterious. There is a +12V lead to it, which is operated "cyclically" (say, 30-40 times a second, more on this in a second), and then the other lead of this normally-open relay goes to the motor armature. There are two other "sets" (where each set is a pair of push-on connectors) on the relay which operate the relay. This is controlled from the seat control switch, but I haven't yet traced the wiring. It APPEARS to be operated in a +/- switched fashion by the seat controls. When operated by hooking 12V to it, it chatters cyclically, as I mentioned earlier, effectively closing the "hot" connection to the armature wiring. Other than the "cycling" (which may or may not be normal), all components seem to be operating satisfactorily.

I can apply +12V to either of the field coil wires and the motor will turn slowly, very slowly, probably just due just to the action of the field coil and residual magnetism in the armature. The armature+brushes have continuity. However, applying 12V to one field lead (or the other) and the armature concurrently causes no movement whatsoever (strange ).

I would like to know if anyone could provide me with a synopsis of how this thing should operate, particularly of the nature of the "cycling" in the hot lead to the armature (whether this is normal or not). Or better yet, a small .jpg file from a schematic for a GM model that might utilize this power seat arrangement.

I would appreciate any insights you can offer.

Thanks, Tom

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Old 02-06-2007, 01:36 PM
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This sounds like a style of DC motor where the armature is separately exited.
For the motor to run 12 volts must be applied to the armature windings.
The field is controlled by the pulsing relay. This is the circuit that passes thru the brushes.
In addition to the pulsing contacts the relay may have a steady set of contacts the control the armature.
The pulsing relay is sometimes called a chopper controller. This prevents the motor from running to fast in cases where the seat (due to a persons weight) may assist the operation thus permitting the motor to have no load. This will also prevent the seat from slamming to a stop at end of travel.

To reverse the direction of the motor the FIELD leads are reversed.

A control switch will be needed to operate the (3) transmission solenoids at the same time as energizing the motor relay in forward or reverse.

Check to see if more than one of the transmission solenoids can be energized at once. If they can the control switch will need to prevent energizing more than one at a time.

A separate set of relays my be needed to reverse the motor.

Do you have the control switch?

let me know if I'm on the right track.

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