Okay, the chugger does have two contacts, one for hot and one for ground, I've never seen one grounded to frame through the bracket.
There are three components, the chugger coil, the leaf switch (triggered by the axle cam) and the switch in the cab.
First I'd check the coil for function (does it buzz when power is applied), the cab switch (is it all intact) and the leaf switch (are the copper contact strips intact).
If it all looks good you can begin wiring it. All the components are wired in series and as such it really makes no difference what order they're wired in. I wired mine (400E) from the hot terminal on top of the motor to the switch in the cab, from there to the chugger coil, and from the coil to the leaf switch. The leaf switch usually has a short piece of wire attached to one strip which is then wrapped around the switch mounting bracket screw in order to ground it out.
As stated, the coils and cab switches are available but the leaf switches are not. If your leaf switch is damaged, it may be possible to repair it or replace it with a modern micro switch. On my 400E, one of the copper strips was broken. I removed the rivet holding the switch together, drilled and tapped the bracket for a 2-56 screw, and screwed a short length of coil spring to the bracket. Then I reassembled the switch with a small (4-40, I think) screw. Now instead of the copper contacts closing together, the remaining copper contact contacts that coil spring which is connected to ground and completes the circuit.
