View Full Version : Riddle me this Batman! (wiring question)

03-31-2015, 09:35 PM
So I've traced every wire that goes through the distribution panel and this one situation has me stumped. We are looking at a bilge pump switch with a positive in wire (red) and a wire for the "automatic" setting which powers the float switch and one for the "manual on" setting of the switch that forces the bilge pump on.

Okay, here comes the mystery. Someone has added a black wire to the "manual on" terminal and it goes to the engine instruments. It goes through that little thing in the upper right corner which looks like a diode to me. And guess where it attaches? To a ground terminal on the engine temperature gauge. (All the gauges ground terminals are connected together).

Why would any positive wire go to the ground on the engine instruments? Why a diode and why from the "manual on" terminal of the bilge pump?


Tom Lathrop
03-31-2015, 09:46 PM
Mystery wiring sometimes remains a mystery. What you explain sounds like the diode is wired to block positive voltage from ground but will allow negative current to pass and activate something or other. Its a kind of control I have used long ago but have no idea what it might be for here. More investigation needed to see what may apply negative voltage to the red wire. Find that and you have the answer.

03-31-2015, 09:47 PM
That is odd. You are sure that the black wire going through the diode goes to ground?

If it does, it might be some attempt at a snubber. When an inductive load is switched on or off it generates a voltage spike, so it is possible that they had some issue with the radio crackling or something else annoying when they flipped the switch. The diode will short circuit the negative spike and reduce the noise.

If the diode were hooked up the other way, it would instantly be destroyed or blow a fuse somewhere.


03-31-2015, 10:08 PM
Doesn't make any sense to me. This bilge pump also went through the main distribution panel so maybe that has something to do with it? I think I'm going to disconnect the diode(d) wire and eliminate going through the distribution panel. I'll rely on the fuse that is there at the switch and hook directly to the battery which I have always understood is the right way to do it.

04-01-2015, 07:14 AM
I'm not too adept at electrical stuff but the snubber theory sounds plausible to me. But would you want your spike to run to the ground on your instruments? Maybe it doesn't matter which ground it goes to.

Tom, all the wires run back to the bilge pump except the one that goes to ground and the positive in wire that comes from the distribution panel.

I'm getting a continuous circuit signal on my tester when I check the positive wires to the ground. That can't be good can it?

I checked the wire several times to make sure I was right. But I'm going to check it one more time to be sure I haven't made a mistake.

04-01-2015, 07:48 AM
Yes--I just pulled the wire and it was going to ground. This is a diode right? Looks more like an LED to me but I know little of such things.


04-01-2015, 07:53 AM
DUHHHH! It is an LED! What an idiot I am. It is easy to see now that I got it out in the light. It is the bilge "pump on" LED light which, of course, needs a ground. It had fallen out of its holder on the panel switch which fooled me into thinking it was an in-line diode.

I still have a short in this circuit I need to figure out.


Tom Lathrop
04-01-2015, 08:14 AM
Yep, Another version of garbage in, garbage out axiom. We make assumptions that guarantee taking the wrong course sometimes. No sweat, it happens and we all are guilty now and again. Disconnect the red wire and check if the short is still there.

04-01-2015, 10:19 AM
LED? Looks like an incandescent light bulb. You might want to grab a basic book on boat wiring and electrical systems before going much further.

If you have a short start at the pump, disconnect it, if that isn't the problem follow the wiring back, disconnect at the switch, try again.

Your idea of bypassing the panel is not a good one. You want to have the fuse/breaker as close to the battery as possible to protect as much of the wiring as possible. Ideally the panel should be close to the panel and if more than 4 or 5' should have a separate fuse/breaker to protect the whole system.

http://Alan https://sites.google.com/site/helium12sofsailboat/

04-01-2015, 11:27 AM
Yeah--probably is an incandescent. I can see the element. LEDs have more of a "plate" don't they. I'm probably not as ignorant as I sound--my brain jumped to the wrong conclusion based on the light not being in the switch, the short, and the wire going to a ground in an odd place.

I've got Calder's book and Sailboat Electrics Simplified. The latter is particularly good for folks like me who know little.

Calder recommends (and I always thought) the bilge pump should go directly to the battery and not through the distribution panel. I would, of course, make sure there was an inline fuse protecting such a circuit since it would not go through the breaker. Is there a reason to have one of the pumps use a breaker instead?


Phil Y
04-01-2015, 03:00 PM
LED Light Emitting Diode. So,yes, it could have been both a LED and a diode I guess. But the bilge pump On light makes sense of it anyway.

04-01-2015, 06:13 PM
I can't cut and paste we'll from my phone. What you have there is a Rule Bilge Pump Switch Panel. Google that and add the word " diagram" and all will be revealed.


Sent from my iPhone using Forum Runner

Edited: On the plane and opened the notebook.

Tom Lathrop
04-01-2015, 08:36 PM
I can't tell just what kind of device it is from the photo. It can't be just an LED since they will only take about 3V or less and need a current limiting resister for 12V which should be easy to find in the circuit. If its an incandescent 12V light, that would explain the apparent short circuit since the resistance of the bulb would be very low when cold. Can only guess and nigh impossible to analyze a problem without full information.

04-01-2015, 08:58 PM
It's incandescent. There is no resistor.

Kevin has found the correct wiring diagram. Thanks Kevin. It matches what I figured out using my tester.

Tonight, I pulled and cut off all the wiring to the switches and pumps and tested just the switches and pumps. I didn't find any shorts in the devices.

04-01-2015, 11:30 PM
So what is the issue with the wiring? Does something not work or blow a fuse/breaker?

The wiring of that bilge switch looks wonky too. Is there anything connected to the cold side of the fuse? It looks to me like someone soldered a black wire from the hot side tot he switch common terminal, instead of going from the cold (fused) side...Weird to have a wire soldered to a spade connector like that.

To trace this, start at the hot wire. Use a volt meter or a test lamp. Determine that with the breaker on, the red wire is actually 12 V.

If so, then check to see that the fuse cold side (the metal band down near the black plastic threads) is also 12 V. If not replace the fuse.

Move the black wire from the hot spade to the cold ring. I'd replace it with a red wire BTW..You can probably solder to the ring. It looks like the ring had a solder lug that probably broke off, so some doofus soldered the black wire to the input (hot) side of the fuse instead of the output (cold) side.

Disconnect the wires from the manual and auto sides of the switch, and check that each of the with contacts gets 12 volts when the switch is switched in the corresponding direction. Test continuity to ground for the manual wire.

If all these check out, then reconnect the wires and power it up with the switch in the OFF position. Put the meter on the manual side of the switch and turn the switch on. It SHOULD go to 12 volts and the pump should be on. If it jumps to 12 volts and then back to zero, and the fuse is blown, then you have a short on the manual line. My guess here would-be that the pump is bad. Try swapping in another pump, or just replace it. You can do s similar test on the auto side, except you will need to manually move the float switch.



04-01-2015, 11:40 PM
It's incandescent. There is no resistor.

Kevin has found the correct wiring diagram. Thanks Kevin. It matches what I figured out using my tester.

Tonight, I pulled and cut off all the wiring to the switches and pumps and tested just the switches and pumps. I didn't find any shorts in the devices.

Sounds like a good outcome then, likely some damage in the wiring from it being compressed somewhere or had something dropped on it and resolved once you replace the wiring with new.

04-02-2015, 10:25 AM
A small incandescent bulb can act as a resistor by limiting current. It was a good way to limit current and provide an indicator when something is running. It also acts as a rudimentary fuse. Granted when cold, it wouldn't resist much, but once on, it would provide good resistance. Make sure that you aren't removing a resistance that is needed in the circuit (or a "fuse" for that matter).