No neutral or reverse

I have a 1972 Evinrude 100 HP with electric shift. I took it out for the first time yesterday and discovered I have no neutral or reverse. I can engage the neutral button and the control and the motor will start. The previous owner said this happens "sometimes" but will switch into neutral after a few tries. I also found out he was running standard gear oil in the lower unit for at least 1 season. I have already drained the old oil and replaced with premium blend (prior to my boat ride). I don't know much about how this electric shift works, but is it possible that the parts are still just gunked up with the old oil and will start to work with a little bit of time? Otherwise, any suggestions on how to diagnose and correct?

Thank you.

Re: No neutral or reverse

(Hydro Electric Shift System Explained)
(J. Reeves)

The shifting setup of the lower unit is what's called a "Hydro Electric Shift", which is quite complex consisting of voltage being applied to solenoids in the lower unit which in turn change oil passages via a oil pump that supplies various pressure on a spring loaded shifter dog. The wires leading to the lower unit (at the powerhead) are "Green" and "Blue". The engine must be running or cranking over in order to shift out of forward gear.

You CAN NOT use HI VIS lube in that lower unit. You MUST USE what OMC calls "Premium Blend" lube, commonly called "Type C". (A thinner lube)

Note: The engine must be running OR have the driveshaft turning by some other means in order for the engine to shift.

In neutral, you need 12v to the "Green" wire.
In reverse, you need 12v to both wires, the "Green" one and the "Blue" one.
In forward, there should be no voltage to either wire. (The spring loaded shifter dog forces the unit into forward gear)

To check the lower unit for proper shifting to make sure you have no trouble there, remove the spark plugs to avoid problems and to allow a higher cranking speed.

This next step eliminates the actual shift switch in case problems may exist there.... Disconnect the blue & green wires at the knife connectors (the rubber insulated boots) leading to the lower unit at the powerhead, then using jumpers, take voltage direct from the starter solenoid to apply voltage to the "Green" wire for neutral, then both wires 'Green" & "Blue" for reverse (Remember the engine must be cranking over in order to shift).
With no voltage applied, the unit should be in forward. No need for a ground jumper... the lower unit's already grounded. You may crank the engine with the key switch or by energizing the starter solenoid with a jumper wire.

Re: No neutral or reverse

As you probably know, this unit is always in forward when at rest. The engone must be turning over, or running to shift. To isolate this problem, or to just check the gearcase itself. On the right side of the engine you will find a pair of wires, blue, and green going into the top of the exhaust housing. Disconnect these two wires. Twist the wires going into the exhaust housing together. Touch a positive jumper wire from the starter solinoid, or the battery itself to these two wires, The gearcase should shift to neutral, again with the engine running, Touch the jumper to the single blue wire, the engine shoud shift to reverse. If it passes this test, check the switch, and wiring, and all connections.