Supposedly simple wiring question

[Paul M]

Hi all:

Both of my bow running lights on my 1973 Morgan recently quit working. I assumed it was bulbs and replaced, but still not working.

I then checked voltage inside the sockets and both show 13V. The bulb sockets are old so I bought 2 new ones assuming the issue was with the lock in pins inside the housing. Still not working.

I connected wires directly to battery posts and light works.

I've checked stripped wire voltage using a digital and analog meter and both show 13V. I even ran a ground directly from battery post to socket and verified voltage at 13.

When I touch wires together there is no spark.

If anybody can help me troubleshoot this, I'd really appreciate it.

Thanks in advance!

Cheers,

Paul

[BambooSailor]

Did you check voltage while bulb is installed and on or without a bulb? If later, symptoms would suggest very loose/rusted/broken wire or somehow compromised connection with high resistance somewhere in the circuit. In such cases, voltage still shows OK (because there is a weak connection but no current is running), but as soon as you allow any current in the circuit, voltage drops based on how much resistance the current encounters. That's why you would not get any spark. Measure voltage while the bulb is connected to see if that is the case.

[Paul M]

No I didnt. Great suggestion though. The terminal end at the socket is freshly cut and stripped. The wire there seems fine. After a cold beer, I'll crawl into the engine room and see if I can locate the other end and assess it.

Just when I thought I was getting a very slight grip on marine wiring, a simple issue like this has thrown me a curve ball.

Thanks for the help.

[hellosailor]

Odds are that the wires are so badly corroded, or some of the contacts are so badly corroded, that they cannot carry any large current. So, with no bulb and no current draw, yes, 13V gets through. But as soon as you try to draw current, the corrosion restricts it and just turns it into heat.

You may be able to eyeball the problem but if the wires are not tinned, are old, and show lots of green and black corrosion at the ends? Time for new tinned wiring. Insulated wires "breath" as the air heats and cools, so moisture actually gets into the whole length of the wire and attacks it all the way through.

[Reefmagnet]

As has already been said, always check the voltage under load. Checking voltage on an unloaded circuit with a high resistance digital meter won't really tell you anything in this situation.

In my experience, bulb sockets are terrible for poor conductivity once they get on a bit. Check any screw connections and give all socket contact points a light scrub with fine emery cloth followed by a rinse with electrical contact cleaner - even the inside of the metal housing if of the screw in or bayonet type.

[Wotname]

Originally Posted by Reefmagnet

As has already been said, always check the voltage under load. Checking voltage on an unloaded circuit with a high resistance digital meter won't really tell you anything in this situation.

.......

Reef is right!

This is the key to all trouble shooting of simple DC circuits. If readers take nothing else from this thread, take what Reef has written as gospel.

And if you ever doubt this, Ohms law and simple maths proves it.

[Paul M]

Good call guys. The voltage dropped to 0 with load.

I then used a 35ft wire to connect from battery to black with whites still connected and nothing.

Then tried connecting battery directly to white wire and leaving existing black wire circuit in place. Shazam, the light came on.

Now I atleast know the problem is in the white wire.

[Wotname]

Originally Posted by Paul M

Good call guys. The voltage dropped to 0 with load.

I then used a 35ft wire to connect from battery to black with whites still connected and nothing.

Then tried connecting battery directly to white wire and leaving existing black wire circuit in place. Shazam, the light came on.

Now I atleast know the problem is in the white wire.

Good work.
Now look for corrosion anywhere along the white wire and look first at the fuse, the switch and where the whites are joined together.

[guyrj33]

Originally Posted by Wotname

Good work.
Now look for corrosion anywhere along the white wire and look first at the fuse, the switch and where the whites are joined together.

I had a butt splice buried inside the wiring harness on our boat.

[Matsubob]

I have just run new wiring to my running lights because of a similar problem. Only I could no longer get more than a 2V reading. The wires were black, no matter how far back I stripped. Now, the running lights show brightly once again!
But running new wire forward on a 30' goes through a lot of cubby holes, so it meant removing panels and trim but the work paid off!
Good LUCK!

[S/V Alchemy]

Originally Posted by Reefmagnet

As has already been said, always check the voltage under load. Checking voltage on an unloaded circuit with a high resistance digital meter won't really tell you anything in this situation.

In my experience, bulb sockets are terrible for poor conductivity once they get on a bit. Check any screw connections and give all socket contact points a light scrub with fine emery cloth followed by a rinse with electrical contact cleaner - even the inside of the metal housing if of the screw in or bayonet type.

^^^This. 18-22 ga. untinned wire original to the boat (45 years now?) is almost comically likely to be shot, a warm green mess at least partway along its length. Just replace it and the sockets at the same time. If the housing and the lenses aren't shot or glazed over, they are fine to keep.

Consider that were this a vintage car away from salt water, you would have done this job twice already!

[S/V Alchemy]

Originally Posted by Paul M

Good call guys. The voltage dropped to 0 with load.

I then used a 35ft wire to connect from battery to black with whites still connected and nothing.

Then tried connecting battery directly to white wire and leaving existing black wire circuit in place. Shazam, the light came on.

Now I atleast know the problem is in the white wire.

The problem is likely both wires. Go to new and tinned. The good news is that if you're going to LEDs, you can use light gauge wire which should be easier to snake to the front of the boat. The old wire can be the messenger.

[boeing1]

would agree that the wiring is the problem, either a high resistance connection or corroded wiring

[hamburking]

I had this exact same problem. Very frustrating.

As others have already said...must check voltage under load. A badly corroded wire or bad connection can show full volts, but provide no current.

[stormalong]

You referred to the WHITE wire. That infers that the wire is not marine grade tinned.

The company that built my boat used black and white untinned wire. I replaced every wire but one that is burried under cabinetry.

Surprisingly, they used tinned wire for the AC outlets and they are still good. My guess is that they couldn't find stranded triplex wire untinned and had to spend the big bucks for the right stuff.