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New to me Tartan 3700 - wiring question

forbin

.
Nov 4, 2013
161
Tartan 3700 Seattle - Elliot Bay
I recently bought a Tartan 3700 and I'm trying to troubleshoot an issue with two of the courtesy lights. I was wondering if anyone has a wiring diagram or could explain how they're wired. My knowledge of marine wiring is limited but I should be able to figure this one out.

The lights are wired to a switch by the companion way entrance. The interior lights all work, but the two outside, in the cockpit and behind the transom platform do not. It looks like there is low voltage at the two exterior lights, but that's as far as I can get.

Brian
 

jviss

.
Feb 5, 2004
4,603
Tartan 3800 Westport, MA
Brian, I don't have those lights, or that switch on my 1996 T3800, hull #20. Could it be an owner addition?
 
Mar 6, 2008
674
Catalina 1999 C36 MKII #1787 Coyote Point Marina, CA.
What do you mean by there is low voltage there. What voltage are you measuring with the fixtures disconnected. Turn on the running lights and see if they work.
 

forbin

.
Nov 4, 2013
161
Tartan 3700 Seattle - Elliot Bay
Brian, I don't have those lights, or that switch on my 1996 T3800, hull #20. Could it be an owner addition?
I thought it was, but it shows the lights (same locations) as an on the diagram in the manual, but it's not clear on the wiring.
 

forbin

.
Nov 4, 2013
161
Tartan 3700 Seattle - Elliot Bay
What do you mean by there is low voltage there. What voltage are you measuring with the fixtures disconnected. Turn on the running lights and see if they work.
There was one light in the aft cabin that was not working (in addition to the outside ones) so when I replaced it, I measured the voltage at the light and it was as expected, and the light worked after it was replaced. I assumed (incorrectly) that the exterior lights would start working if I replaced them as well, but when I cut the wires the voltage measured at the wires going in to the "fixture" was below one when the switch was on...so those particular lights are not getting power. I'm assuming they're all on the same circuit and wired in parallel, but I don't know how to troubleshoot much beyond what I've already done because I can't trace the wires.

Brian
 

forbin

.
Nov 4, 2013
161
Tartan 3700 Seattle - Elliot Bay
...but when I cut the wires the voltage measured at the wires going in to the "fixture" was below one when the switch was on...so those particular lights are not getting power.
Actually the voltage at the fixture is around 1v, and is not affected by whether the switch is on or off.
 

jviss

.
Feb 5, 2004
4,603
Tartan 3800 Westport, MA
Actually the voltage at the fixture is around 1v, and is not affected by whether the switch is on or off.
You must have a broken wire or other bad connection, I'm guessing.
 

forbin

.
Nov 4, 2013
161
Tartan 3700 Seattle - Elliot Bay
You must have a broken wire or other bad connection, I'm guessing.
Well, I think I'm giving up, but there is definitely a bad or broken connection. The wiring for the two lights that aren't working comes out of a wire run on the starboard side of the hull in the lazarette at the transom and runs first to one light and then the other. There's a splice off the main line to the first light and the main line is wired to the second. There's one joint between the starboard wire run and the lights, and from that joint to the lights, everything is fine, but there's no power getting to that joint and no continuity with the switch at that joint. But that's about as far as I can go.

There is a feed running under the main cabin floor in to the area starboard of the bilge, and then it splits to power the lights on the starboard side of the forward cabin, in the main settee (fridge pump area), under the stove (no access I can find unless I pulled up the floor which I'm pretty sure is glued down) and then back to the transom. I can't access where that split happens, there's no access panels anywhere in the galley, but I suspect that is where the problem is.

The aft cabin and bathroom lights have different wire runs from the panel area (I still can't figure out where any of the runs starts from, maybe a bus bar with the different feeds out to the lights), as do the port side lights under the nav station near the forward bulkhead on the port side, and in the cabinet in the forward cabin (port.)

Anyway, a friend who is a marine electrician is going to take a look when he's doing some other work on the boat in a couple weeks. My guess is it'll take him 5 mins to figure it out or he'll say there's not enough access, just run a new wire. I now know enough that if I could access all the wires I could definitely figure out the problem, but that's not quite good enough!
 
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Likes: jssailem
Mar 6, 2008
674
Catalina 1999 C36 MKII #1787 Coyote Point Marina, CA.
Tools are available to trace wires without cutting them. We inject radio frequency signal at one end of the wire and listen for the signal with a probe at various points along the wire
It is easy to narrow down to the broken point.
We use them in telecommunication troubleshooting. You can buy them for about $200.00 it may save you technicians charged.
Haro.
 
  • Helpful
Likes: jssailem

forbin

.
Nov 4, 2013
161
Tartan 3700 Seattle - Elliot Bay
I figured it out...I feel a little dumb but whatever. The outdoor lights are on a separate circuit wired to a switch next to the engine instrument panel. I had it in my head that the switch was for the lights on the panel, and it may be as well (too bright to see today), but also controls the outdoor courtesy lights. The fixture that was originally there also turns out to be broken, so that probably tripped me up to start with when I originally flipped the switch and didn't see those lights come on.

Learning experience!