There seem to be a lot of posts concerning electrical failure of the model A-71 automatic transmission's "overdrive" circuit on 240 models. Most of the responses posted point to the relay behind the center control console. None of the responses was very complete and one of them (from a guy named "Dick" in the archives) described the function of the relay/solenoid circuit just backwards.

What most people complaining of a problem say is that suddenly the up-arrow indicator on the instrument panel came on and the car shifted back to third gear and they can't get 4th gear to work again, despite pressing the button on the gearshift head. I just had this exact problem.

The "theory," if you will, of how the "overdrive" electrical circuit works goes something like this -- yes, the A-71 automatic transmission is a 4-speed transmission, but, unless the "overdrive" solenoid is energized, it is by default a 3-speed automatic transmission. For example, if the whole electrical circuit is functioning perfectly and you pull the fuse to the O/D you will end up with a 3-speed transmission. I know this is counterintuitive because almost everyone I know uses the A-71 always in the 4-speed mode and never touches the "downshift" switch on the shift knob - people just kick the accelerator to pass and the transmission does an automatic kickdown downshift to third. If for some reason you wanted to, you could hit the downshift button on the shifter head and downshift to third gear, locking out 4th. This is why I do not like calling this whole function "overdrive" - it is not "over"drive, but something more like a "passing gear," a downshift, not an upshift. The old manual tranny Laycock de Normalville overdrives, A and D types, perform an "upshift" - when the solenoid on these babies is energized you get a higher final drive ratio, like fifth gear (.6 or .7 to 1 instead of 1 to 1). But, in the 240 with an A-71 when you hit the "overdrive" button what really happens is you de-energize the solenoid, disabling 4th gear; you get a downshift to 3rd gear and the "up-arrow" light on the instrument panel. I guess that up-arrow or forward arrrow means that you are in hyper-drive or "passing gear." That's why I think it ought to be called a "passing gear" switch instead of an "overdrive" switch. Yes, it's really stupid. The transmission should have been built such that it would function as a 4-speed by default, since that is the way EVERYONE uses it, and then it could have had an electrical circuit to drop it back down to 3rd gear if desired, and if that electrical circuit failed (switch, wires, relay, solenoid) you would end up with a permanent mechanical 4-speed transmission instead of a default 3-speed transmission that winds out and whines down the interstate at 75, guzzling gas and wearing out the engine. Who is the genius who designed this!!!

The reason "Dick" in the archives is wrong is that he says his mechanic "fixed" his problem with the O/D relay by disconnecting the wires to the solenoid. That would give the opposite result - a permanent 3-speed. Instead, the cheater's way to fix this problem is to HOT-WIRE the solenoid, not disconnect it!!! You need power to the solenoid to enable the 4th gear.

What to do?

First check fuse 11 (make sure the number is correct by using the wiring diagram for your particular model). Make sure the fuse ends are clean and it fits tight.

Check for fraying or severing of the wires to the solenoid - under the car on the left side of the transmission. Pay particular attention to the metal retaining clamp near the front end of the shift lever where the wires pass through.

Remove the black plastic shifter boot inside the car (2 phillips screws in the front) and be sure the wires to the switch on the shifter head are in good order.

Okay, like most people, you are now at the point where it is probably the relay behind the center console.

Remove the glove box (open the door and remove the phillips screws around the periphery of the glove box face) - it pulls right out easily. Next remove the carpet cover under the glove box - 3 plastic twist fasteners under the dash edge and 2 retainer clips on the floorboard. Then remove the passenger-side plastic side-cover on the center console (one screw and one plastic twist fastener). Up near the top-left corner of the glove box opening you will see a wire harness that goes left to a white relay just behind the center console (and just out of reach!). There should be 2 gray wires, a white one, a blue one (or blue with black stripe), a yellow-red striped one, and a black one. Black is ground; blue or blue with black stripe is hot from fuse 11; white is power out to the solenoid; and the 2 gray wires go to the switch - the gray wire on the same connector as the blue one is power to the switch and the other gray one is control power from the switch back to the relay. If you want to cheat and save money, pull the plug off the relay and make a short jumper wire with male spade terminals on each end and jumper between the white wire and the blue or blue with black stripe wire on the harness plug - this puts power from the keyed fuse straight to the solenoid, eliminating the relay, the switch and the "passing gear" up-arrow indicator light - you end up with a hard-wired 4-speed automatic transmission. If you don't want to cheat, plug a replacement relay into the harness plug and push it into the cavity next to the glove box opening where there is plenty of room for it - to hell with trying to get back in behind there and remove the old dead relay; just leave it.

I hope this helps some poor soul.

Roger