[C320-list] Bow running light wiring problem

[Jeff Hare]

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)