[C320-list] Bow running light wiring problem

[Scott Thompson]

Agreed that the ground circuit could be the problem. The weirdest 
electrical problem I ever saw on a boat occurred when the ground 
connection from the main panel to the engine block broke. When I turned 
on running lights the current found an alternative path to ground 
through the windings of the engine blower motor (which shared a common 
ground wire with the stern light) then to a common positive connection 
on the ignition switch (turned off at the time) to the oil pressure 
alarm to the oil pressure sensor, and then through the oil pressure 
switch to the engine block. So when I turned on the running lights the 
oil pressure alarm went off even though the engine wasn't running and 
the ignition was off. Took a while to track that one down!

On 7/18/2015 1:33 PM, Jeff Hare wrote:
> I suspect you're focusing too much on the positive wire. The bad connection
> could be in either the positive or negative lead and more often than not,
> it's the ground, especially if you see voltage at the device but the device
> doesn't operate.  It could be a weak floating ground or ground short you're
> measuring.
>
> You didn't say where you measured the voltage and how you determined the
> resistance in the positive lead.  If you measured the voltage across the
> terminals of the light fixture with the light off, then the resistance you
> see (20?) was that of the bulb.  When the light is turned on, then you
> cannot measure resistance directly, you have to measure the voltage across
> the bulb and do the math.
>
> If you have a long piece of wire, clip it onto the battery negative post and
> lead it up to the light fixture.  Test it using the power lead and this new
> ground.  If it lights, the positive wire is ok but the ground is faulty.  If
> it does not light, then move the wire over to the positive side of the
> battery (carefully) and see if the bulb lights with this new positive lead.
>
> To measure resistance of the power and ground wires, you can do it a couple
> ways but the easiest is to turn off the breaker, take this long test wire
> you just used (14ga or so) and clip it to the positive lead on the light
> fixture and lead the other end back to the breaker panel.
> So: With the meter in the ohms setting, measure the resistance with one lead
> on the test wire and the other on the switched side of the running lights
> circuit breaker.  The test wire will not add anything significant to the
> resistance as far as this test is concerned. You should see under an ohm or
> so from the wire, but should see several ohms across the bulb (20 or more
> I'd guess) .  .  You'd do the same thing with the negative fixture lead,
> only using the battery terminal as the test point.
>
> Quite often grounds are overlooked or undersized.  It's of course not enough
> to get positive to the device, you have to have equal carrying capacity on
> the ground leg as well.
>
> -Jeff Hare
> #809
>
>    
>
> -----Original Message-----
> From: C320-list [mailto:c320-list-bounces at lists.catalina320.com] On Behalf
> Of Joseph A Tamucci
> Sent: Saturday, July 18, 2015 12:31 PM
> To: c320-list at lists.catalina320.com
> Subject: [C320-list] Bow running light wiring problem
>
> My bow running light no longer functions. THE STERN RUNNING LIGHT WORKS
> FINE.  After troubleshooting, the result is that there is some resistance
> (20 ohms) in the positive wire at the bulb fitting (11.3 volts is read).
> I have disconnected the positive wire lead and cut the lead exposing the
> wire itself. I have  cleaned and stripped back the wire. Even after doing
> this,  when the bulb is connected across the wires the voltage drops to near
> zero and the bulb does not light. I have temporarily run an external wire
> directly from the electrical panel switch to the bow, and using the existing
> ground wire,  got the bulb to light so that confirms the faulty positive
> wire.  Looking at the wiring schematic in my 1999 C320 manual (hull #619)
> and looking at the running light switch, there is a single wire coming off
> the switch which goes into the wiring harness and somewhere within the
> harness (under the port seat?) there is a splice that splits the wire into
> two wire runs running to the bow and stern.  The schematic does not identify
> where the splice is located.  Somewhere between this splice and the end of
> the wire at the  bow bulb fitting the wire has developed a bad connection.
>
>   
>
> Has anyone had this problem, and found where the splice is physically
> located in the boat?  I know that the wire runs inside the bow pulpit and
> into the boat somewhere by the anchor locker and through the portside
> overhead channel where the port cabin light is.  I intend on removing the
> portside molding and start tracing from there.  Any information on this
> subject would be much appreciated!
>
>   
>
> Joe Tamucci
>
> Andante (hull #619)
>
>   
>