Lionel OO 2-Rail Hudson Whistle & E-Unit Wiring

There is some info on the American OO Today blog. Hope this helps.

https://americanoo.blogspot.com/search?q=Whistle

I'm still trying to figure out the wiring for the whistle relay and why the whistle doesn't engage, but I ran into another issue.

After a good amount of running, the reversing unit in the locomotive decided to stop working and it's stuck in neutral. No familiar buzz (even at higher voltages) to tell it's working.

If anyone has some wiring diagrams or is very experienced in servicing Lionel OO products, I'd really appreciate you chiming in!

I am not familiar with OO locomotives, but that same e-unit is used in the 227 family of O gauge switchers, which I do have some experience with. There is a horizontal coil which operates a paw that engages a ratchet wheel to reverse the motor. One end of the coil is connected to the same frame ground the e-unit uses for the motor.   Looking at the contact board it is the lower left contact. The other end of the coil wire goes to an eyelet on the fiber board spool that the coil is wound on.  An insulated wire is then connected to this point and goes to a power connection.  On the switcher it is on the brush plate where the e-unit can be turned on and off. 

The coil connections are somewhat fragile and can be troublesome.  Also overheat coils are not uncommon.  This can be seen by blackening of the wire varnish  on the switchers I attribute this to running the loco at too high a voltage.  It is designed for 12 volts.  It is easy to check the coil with a meter or a jumper.

Another potential problem is where the shoulder screw is tightened against the contact board with a lock nut on the outside.  The tension on this screw needs to be just right so the ratchet wheel will turn freely, but is not loose.  If the shoulder screw has been over tightened in the past, the contact board material may be crushed.  This can be repaired with a very small appropriate sized washer between the screw’s shoulder and the contact board.

Once properly adjusted the OO e-unit is usually very reliable.  I prefer it to the 259E e-unit used in most late prewar and most post war locos.