The diagram above shows the wiring. The power supply (battery, charger connector and charge indicator ) is on the left, the distribution terminals in the middle and the loads on the right. The 12 volt system is not a shock hazard. However, the battery can supply considerable power through the high current capacity so large size wire is required (10 to 12 gauge for the 25A circuit, 12-14 gauge for the 15 amp circuits and 16-18 gauge or the lower current circuits). Note that all the circuits are fused. This is to prevent the wires from melting in case of a short circuit (best keep the fire in the fire box). The subsystems are individually fused so that a short can be isolated to a subsystem.
Some of the individual components are described next.
Terminals: Crimp terminals were used on the wiring connections to the relays and between the subsystems. Ring type terminals were used on the battery connection and to grounding screws. Spade type terminals were used on the connections to the power terminal strip. Blade type terminals (1/4" wide) were used on the connections to the relays and in series (male + female) with the leads to the switches.
The photo above shows the "bulge" in front of the oil tank. The switches at the top are igniter (red), water pump (black) and air compressor (toggle). The light switches will go between the push button and toggle switches. The brass thing on the right is a modified Clippard regulator used as a brake valve ---- see Brake Valve. The black lines connecting the brake valve are Clippard 1/8" ID hose. That is the power terminal strip below the switches. That terminal strip was found in the junk box. Suitable terminal strips are available form Radio Shack, McMaster-Carr, etc.
The power switch is on the lower right. The side of the cab and oil tank are about 1" outside the frame channels so the body of the power switch will be up inside the empty space below the bottom of the oil tank. The toggle handle will stick out below the level of the cab floor.
That is the water pump on the left side of the photo. The water pump relay is in front of the pump.
Battery Charge Indicator: The charge indicator was mounted in front of the Johnson Bar and Park Brake levers as shown in the photo above. An angle bracket was used to mount the indicator. This area is normally dark so the LEDs will be easy to see. The lowest LED is a "power on" indicator. Hopefully these indicators will also serve as a reminder to turn off the power switch when the locomotive is shut down.
Igniter: The igniter is shown above. It was desired that the igniter be removable as a unit for test and repair so all the parts were mounted to a chassis. The chassis is this case is a 7" length of 2" X 2" X 1/8" angle. The coil was secured to the angle with RTV. The aluminum angle with the relays was secured to the chassis angle with a single screw. This orientation of the relays keeps most of the wiring below the relays and protected. The large power resistors were secured to the coil with RTV and the wire leads covered with heat shrink tubing. The steel angle is secured to the floor plate with a couple screws. The red wire is the power lead and the yellow wire is the control lead that connects to the push button switch. A 20" spark plug wire with boots was purchased at the auto parts store. The boot at the coil end was removed, the wire cut to the correct length and the crimp end reattached. The boot that was at the coil end was discarded.
The photo above shows the igniter installed between the battery and the power terminals. The yellow control wire connects to a mating yellow wire from the red pushbutton switch. (The blue wire to the the black pushbutton switch goes to the water pump relay. The green wire is from the toggle switch and will connect to the air compressor relay.) The dark charcoal colored spark plug wire is visible on the right --- it runs in the space between the frame channel and the frame side to the sparkplug.
Air Compressor: The air compressor was not part of the original design -- the original plan was to use steam as a backup if the steam powered air compressor failed. When the electrical compartment was being laid out using the actual water pump, battery and igniter components it was discovered that there was room for a small compressor. The compressor is a Harbor Freight item #96068 that has been modified to fit in the available space --- see Electric Air Compressor page in Brakes section. The compressor is clamped to a small 1/8" steel plate which is attached to the right fame channel with a couple screws. The control relay and the pressure switch are mounted to the under side of the steel plate.
Photo above shows the compressor secured to the right frame channel. The relay and pressure switch are between the frame channel and the frame side. The compressor output is via the blue hose.
This is the rear view of the electrical compartment with everything installed. The oil line runs vertically from the gap behind the air compressor ---- between the right frame channel the frame side to the bottom of the oil tank. There is shutoff valve on the lower end of the oil line and a quick connect on the output side of the shutoff. The oil filter connects to the valve via the quick connect. The oil tank can be removed by closing the shutoff valve, disconnecting the oil filter and then lifting the tank off.
The light circuits will be designed later and documented in a separate page.