RUNNING LIGHT HAS 12V BUT WONT LIGHT

Steve255AJ

Steve255AJ

Member
Sep 29, 2021
56
Six Mile , SC
Boat Info
255 AMBERJACK, 1985
(trailered on) VENTURE COMMANDER SERIES 7300
2018 F150 XLT w/ 5.0L V8
Engines
5.7L (350) 260HP; SINGLE. ALPHA 1
Okay I'm back, the boat is really coming along nice and I want to thank everyone who gave me advise on my last problem with the water leak which is completely fixed.
I have another, small but annoying, problem which I'm hoping someone has had and knows how to fix.
I've got every single electrical feature on my boat is working perfectly, EXCEPT,...the port running light.
I have cleaned all the contacts and tested the contacts for voltage and it's reading the battery voltage 12.5V , I tested the bulb and it's good, lights up on my bench tester no problem. I went out and got new bulbs just to be sure, tested both of the new bulbs and they are good.
The socket seems in good condition, I've wire brushed it and the spring feature works fine and the bulb locks in and makes good contact the two socket points that it should BUT it won't light up!? I took apart the starboard side light to see if there was any difference, it looks the same as the port. I tested all the other bulbs in the starboard light and they all light up. I'm usually very good with electrical problems but this one is perplexing to say the least.
I honestly don't plan on using the boat at night but it just "bothers me" that it doesn't work, lol. I'm sure there are other boaters that feel that way about things like this.
Anyone who could shed some light on this would be a great help.
Thanks in advance, Steve.
 
Steve255AJ said:
...shed some light...
Click to expand...
"Shed some light"; funny...
When checking for 12V at the socket, what are you using as a ground for your test equipment? Even though you have power there, it still needs to find its way back to ground. My guess is that you're missing the ground from the bulb socket.
 
Your not trying to use an LED bulb are you?

Some LED's are polarity sensitive.
 
Are you testing the wires going into the socket, or putting the probes on the actual contact points for the bulb? If the former, you haven't tested the socket itself. If the bulbs are LED, you may need to reverse the wires, ignoring any color-code.
 
Nater,....this socket has two points where the the "two pole" bulb makes contact on, these bulbs have two small round contact points on the bottom, not one. One is positive and one is negative. I verified this by switching the position of my multimeter probes and the voltage read out goes from +12.5 to -12.5 . The "rim" or "sleeve" of the socket that holds the bulb is not the negative as with many other applications that are in 12V systems. You're giving me an idea that I might try though,....maybe I should run a long wire from the neg. battery terminal and test continuity to the negative side of the socket to see if the ground is fouled ??
Jim G,....I'm not using LED bulbs, Good point though because I had a problem trying to convert my motorcycle to LED directional signals and it wouldn't work, I'm using the proper replacement for the factory bulb, they are identical to the bulb that was in it.
Bobeast,....I am putting the test probes right on the contact points for the bulbs.
Thanks for all your suggestions, Steve.
 
Steve255AJ said:
One is positive and one is negative. I verified this by switching the position of my multimeter probes and the voltage read out goes from +12.5 to -12.5
Click to expand...

You have tested and have power to the socket pins, no advantage to running another ground wire to test.
You tested the bulb on a bench supply and it works, so its pins are good and proper.

What brand fixture and what number bulb did you buy?
Do you still have the old bulb? Can you read a number on it?
Compare the length from the side retaining pins to the base contacts.
Are both bulbs the same or is the new shorter? Is the pin alignment the same? side to side and sides to base pins.

Finally if all else checks good, the sockets have either a spring or a rubber base to provide tension against the bulb.
Is the base pushing up firmly against the bulb contacts?
And be sure the base has not rotated changing the side pin to base pin orientation.

side pin to base 90 degree apart
upload_2021-11-24_15-52-12.png
 
Last edited:
Patrick,.... Thanks for all that info and I'm going to verify all that asap.
I'm 99% sure the bulbs are identical because I checked them in the starboard side light to be sure they worked in a "known working socket of the same type" and they all worked including the original bulb.
The spring seemed to work fine and the bulb pushed in and turned to lock as it should and I was pretty sure it was making proper contact in the socket but I'm going to recheck it.
I will recheck it all soon and let you all know.
Thanks for all you help and information.
 
I would assume that the surrounding metal socket SHOULD be the ground.

Use your tester on the working socket to verify. Maybe your port running light socket was replaced and wired incorrectly?
 
Espos4 said:
I would assume that the surrounding metal socket SHOULD be the ground.
Click to expand...
Not necessarily. A single-point center contact; absolutely. However, it looks like he's running the RV-usual BA15d, which has two separate contact points, and does not electrically use the shell. Consequently, the shell may or may not be grounded (or hot).
 
I bet I know the exact problem. I have had the same problem on a couple of my lights. I figured out that the pins on the bulb didn't match the fixture just right. The fixture was just slightly off. And this caused the contacts on the bulb not line up with the locks on the fixture.

Check to see if the bulb lights up plugging it in to the fixture. Plugged in but not twisted to lock it. On both of mine, they would light up half way between locked and inserted. My wires weren't long enough to change them out with a quality fixture.
 
An 1157 bulb is a turn and tail light bulb that has 2 filaments. Both contacts are positive and the bulb grounds on the brass. You need the correct bulb.
 
And on the older ones, the bulb has two contacts for one element. Making the base just a base with a pos contact and a neg contact.

I threw those photos away I guess because I no longer have them.
 
Thanks for all your inputs.
The fixtures are original and the old style. The base (or shell) is not neg. the two contact points are pos. and neg.
I did test the base to see if it's grounded....no go.
The two contact points do line up with the bulb contact points when it locks in.
The bulbs are correct and they do not light at all when turning to lock.
Replacing the fixture would be my preferred solution, however....there is barley any slack on the wire; there is barley any space to fit other than a factory fixture and how do you access the wires underneath without cutting the "fur" lining in the cabin area and messing it all up???
I can't even find where exactly the wire runs. I'm guessing it runs towards the galley and then across on the ceiling of the cabin into the harness that goes to the horn or maybe it runs to the galley cabin light?
Anyway, the boat is at a local marine mechanic right now having the stern drive looked at for a shifting problem so I can't work on it till I get it back but as soon as I have it I will continue to work on the running light and check all these things out.
Thanks again for all your help.
 
Steve255AJ said:
Replacing the fixture would be my preferred solution, however....there is barley any slack on the wire
Click to expand...
If you were to push the guts out through the fixture and snip the wires right at the contacts, would you be able to get enough slack to butt-splice more wire onto the existing harness? That would at least allow you to adapt a new fixture.
Something else to keep in mind; a voltmeter draws an extremely small amount of current and will show power, whereas a bulb can draw enough that a high resistance somewhere in the wire would restrict enough current that the bulb won't light. Are there any other bulbs that are powered from the switch? The switch could be causing your troubles.
 
Mine was the navy lights. The wire was so tight, there was no way to get enough wire up to strip for an extension. It sounded like the same issue. The socket was put into the fixture and then pulled tight from the inside. With out taking the interior completely apart and rewiring from the inside, just no room.
 
It sounds as though when the bulb is inserted and twisted to lock in place the base is also twisting.
 
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