L40 Bilge Pump Wiring and Indicator Enhancement

The Leopard 40 has four automatic pumps. There is one in each engine compartment and one in the main hull space below the floor boards. Unfortunately, there is no way to know which bilge pump is activated when the bilge alarm light comes on. We wanted to enhance the system so that we knew which bilge pump was running, as is done on newer production boats.

The engine room pumps are a very simple connection, with only the FLOAT SWITCH and BILGE ALARM in the circuit. Diodes at position 265 and 266 allow either float switch to provide power to the BILGE ALARM light. There are two bilge alarm lights, wired in parallel, one mounted at the helm and another on the Navigation Station DC breaker panel.

The main cabin bilge pumps have more complex wiring that allows them to be turned on by two methods: a manual circuit-breaker switch on the DC electrical panel or by a float switch located adjacent to the pump. It took a while to figure out how it works, primarily due to time spent decoding the icons on the diagram.

Here is what I deduced from the schematic. (I've noted the alternate connector in parenthesis.)

Power is supplied from the POS BUS-BAR to fuse F269 (F270), mounted in dedicated fuse holders at position 269 (270) in the wiring panel. Automatic activation is accomplished through the float switch. F269 is connected to two connectors on a control relay (outlined in dashed lines). This supplies power to the right-hand side of the FLOAT SWITCH, which provides power to diode 263 (264) when the float switch is activated (red line). The output of diodes 263 and 264 are jumpered together to activate the BILGE ALARM light, which is connected to NEG BUS-BAR - 2 (green line). The input (left or anode) side of diode 263 (264) is also connected to the relay coil, causing it to be energized when the float switch is activated (purple line). The contactor in the relay connects power from F269 (F270) to the BILGE PUMP, which is connected to NEG BUS-BAR - 2 (yellow line). (Don't let my coloring lead to confusion; all of these wires are energized when the float switch activates. I simply use the colors to indicate the section of wiring I'm describing. The description is only for one pump; the wiring and operation is the same for the other bilge pump.)

Automatic Activation

Manual activation is accomplished by switching the Navigation Station DC panel circuit breakers to the ON position, activating circuit 204 (205). This provides power to the BILGE PUMP, but does not activate the BILGE ALARM (red line).

Manual Activation

What isn't shown in the diagrams is that the output of all four diodes (263, 264, 265, 266) are wired together, so that any of the four bilge pumps will activate the two bilge alarm lights. The diagrams also don't show that there are two bilge alarm lights, wired in parallel. The key element of understanding was that power is supplied to the anode (left side) of each diode (264, 264, 265, 266) when that pump's float switch is activated. The alarm modification was then easy to accomplish. 

The anode of each diode is connected to one of four LEDs that I mounted on the DC breaker panel. I used a 22 gauge multi-wire signal cable for the connection (a piece of Cat5 stranded ethernet cable would work), tinning each conductor and sliding it into the screw-down along with the existing wire and tightening the screw. Each wire in the cable feeds one LED's +12v. Diode 263 is Port Main Bilge, 264 is Stbd Main Bilge, 265 is Port Engine bilge, and 266 is Stbd Engine Bilge.

DC Wiring Panel Located Behind Panel in Port-Aft Cabin

I mounted four red LEDs around the main bilge alarm light on the DC breaker panel. The upper left is port engine, the upper right is port main cabin, the lower left is stbd engine, and the lower right is stbd main cabin. The arrows on the picture show the LED locations.

LED Locations on DC Breaker Panel

LED Gounds Connected Together

All four LED negative wires are connected together and run to one of the negative bus bars in the DC breaker panel. 

The finished installation of the LEDs makes it easy to tell which pump is running. 

An enhancement to the bilge pump alarm system would be to add an audible alarm, wired in parallel with the bilge alarm indicator at the helm and/or on the DC breaker panel.

We've also found that the main cabin bilge pumps can be unreliable because the relay connectors on the DC wiring panel may get corroded or the release handles may be accidentally activated, causing the relay to get unseated from the receptacle. Note that athe lower relay's handle is slightly out of alignment, which may cause the pump to not activate. I think that R&C should have used a permanently wired relay instead of something that's easily disconnected. It is useful that the bilge alarm will light when the float switch is activated, regardless of whether the relay functions.

After installing the new LEDs, we have been able to verify that the starboard engine compartment bilge pump runs regularly. We've not seen any of the others run. This information validates our assumption that only that pump has been running (the rudder post leaks - a job that we will fix during this summer's haulout).

  -Terry