The Stovebolt Site Forums The Shop Area The Electrical Bay New LED tail lights very dim

I bought a pair of those LED tail lights, but when I installed one of them, it was so dim I could barely tell it was working - both turn signal and tail light.

My 52 Chevy 3100 is still 6 volt. The wiring harness was replaced about 5 years ago. The LED tail light comes with 3 wires (black,red & white), so I'm assuming the white one is a ground wire. I hooked it to a shiny bolt that holds the bumper to the frame. (I know you guys always say most lighting problems are caused by a poor ground.)

When I touch the wires from the tail light directly to the battery posts, it is definitely brighter. When I touch the wires to my 6 volt battery charger, they are REALLY bright.
The vendor assured me these lights work for 6 and 12 volt systems.

The battery posts are nice and clean, and the cables are fairly new and in good condition. The ground strap from the engine to the frame was replaced a couple of years ago, and looks OK.

Should I expect these lights to be as bright as they were when hooked to my battery charger?

Any suggestions?

should be just as good as connected to the battery . ground strap replacement is a good thing however the pickup is rubber mounted well should be, have the taillights got a good return path to the chassis ? temporarily connect a wire from the taillight mount to a chassis bolt both clean connections see if that improves if so problem is an earth issue at taillight , also test that you have 6v at the pin inside your light fitting could have a corroded connection somewhere
regards
andrew

Are these the 45 LED Tail lights from United Pacific?

If so, according to the instructions on the back they are designed to work at 7.7-14.0 VDC

white wire is ground, black wire is tail, Red wire is stop light.

and they are Bright.

Good Luck

You said they were bright when hooked to your battery charger. What's the voltage output of your charger? The charger output should be north of 7 volt. With a voltmeter check both the output of you generator (at the gererator) with engine running, and output of charger. If the same you have wiring problems. If they are as DADS50 posted, you are at the very bottom of the voltage window and will have dim lights at times.

DADS50:
I bought them from Classic Parts of America. I found a note that indicates the wires are as you described.

BELTFED:
The voltage output of my battery charger is 8.0 volts. The output of my generator (with the engine running) is 7.9 volts.

The following voltages were measured using a multimeter with the negative probe attached to a wire that was inserted between the negative battery cable and the battery post.
With the engine off and the lights on, here's the voltages I've measured:
Battery: 6.2 volts
End of positive battery cable where it attaches to the starter: 5.6 volts
Hot wire feeding light switch: 5.3 volts
Tail light fuse terminal: 5.0 volts
Tail light wire at tail light: 4.8 volts

With the engine running, the voltage at the tail light wire is 6.0 volts.

Are any of these voltage drops significant?

What size and condition is your positive battery cable? You're dropping over 1/2 a volt across that cable with just the lights on - that sounds excissive to me.

A lot of the old 6 volt systms got 12V replacement cables over the years and they just won't carry the load. Some of the 6 volt guys around here use #1 or #0 welding cable with soldered terminals, or 2/0 battery cable.

Your dropping way to much in those circuits. Sounds to me like you've got corosion at most of the connections. I'd redo all of the wire connections leading to the rear end.

DG

To expand on Denny Graham's post. I would also check/clean all ground strap connections. If they don't exist I would add straps from transmission housing to frame, and transmission to the body. The ground strap from your battery needs to go to your transmission as that is the connection that gets the highest current drain during starting. Here's a test...run one lead from your ohmmeter to the ground post of your battery. With a piece of wire connect the other end of your ohmmeter to the place where your tail lights are grounded. If you read anymore than a few 10ths of an ohm....Bingo, you need to add straping to body panels or start cleaning bolt and screw connections on your sheetmetal.

Waldo35,
How can I tell what gauge my positive battery cable is? It's a fairly new cable with cloth insulation that I paid a good amount of money for. It is 0.5 inches in diameter (including insulation).
According to the wire gauge table I found online, an 00 gauge wire is 0.36 without insulation.

Beltfed,

I already have a grounding strap from the frame to the bellhousing. I will add a grounding strap from the body to the transmission. If it ever stops raining here in Ohio, I will clean the existing ground strap connections, and then clean the connections of any wiring from the battery to the tail lights. Is there something I can use to keep these connections from corroding, or at least slow it down - like a paste or a spray?

Sorry BillyDon, I misspoke. The wire to the bellhousing is the one I said take to the transmission. It is the one that should come off your battery post as it sees your heavy starter current. All others can start at your bell housing and go wherever. And now, Yes they do make a conducting paste. It consists of ground copper powder in grease or paste. "Loctite" brand comes in a stick (like a lipstick tube), other in small tubs. Find it at an electrical parts place or maybe Lowe's or Home Depot. Run the test I posted earlier and find out if you really have that problem before spending time and energy. Good luck.

Beltfed,

Finally a sunny day. The resistance between where I attached the ground wire at the rear bumper and the wire I ran from the negative post of the battery is 29 ohms! Oops, it seemed like a good place for a ground. When I touch the probe to the body back there I get 0.0 ohms. I will move my ground wire and let you know if that helps.

I think you found your problem, that's gotta make a BIG difference with an LED. They already have resistance in the circuit to cut down the 12v to a usable 1.5v to 5v depending on the LED that they are using. Add 29Ω to that and you've got your dim bulb situation.
Denny Graham
Sandwich, IL

If I add a ground wire from the bell housing to the body, does it have to be one of those wide,flat braided ones, or can I just use a fairly large insulated wire?

Does not matter you could use #4 solid copper if you want. Myself I would run the bond from as close to battery and to as close to lites as I could. I hate frame grounding - nothing but troubles.

Dan Bentler

Update: I have run ground wires (old extension cord, thanks to a tip I read on here) from where the negative battery cable attaches to the frame back to each of tail lights. I now have 0.1 ohms between the negative post of the battery and the ground wire at the tail light.
But the lights were still way too dim. Starting at the positive battery I have cleaned or made new connections all the way back to the tail lights.

Here are my voltage readings now with the headlights on:

Battery: 6.1 volts
Battery cable connection to starter: 6.0 volts
Ammeter: 5.9 volts
Connection at light switch from ammeter: 5.8 volts
Fuse box in: 5.6 volts
Fuse box out: 5.6 volts
Junction at back of truck where tail light wire splits off to both tail lights: 5.2 volts.

So it looks to me like that last reading is excessively low. When I separate the wires at that junction, the voltage of the wire coming from the front is 5.6 volts. If I add the wire going to the left LED tail light, it is still 5.6 volts. But as soon as I add the wire to the other tail light, the voltage drops to 5.2 volts.

Is that normal? The other tail light is still my old one with bulbs, and I haven't checked the connections from that junction to it yet. I am using a wire nut to make the connection at that junction. Is that a no-no? I like being able to take it apart.

Final update. I have a 6/12 volt battery charger. Set at 6 volts, it puts out 8 volts according to my multimeter. Hooking the LED tail light wire up using the charger as the power source but still mounted on my truck and using the new ground wire I ran, I get a much brighter light. Set at 12 volts, I get a really bright light.
Hooking up the LED brake light wire with the charger set to 6 volts (8 volt output), I get a light that blinds me and leaves spots in my eyes.

My conclusion is that these LED lights need more voltage than my 6 volt battery can generate.

With my engine running at a fast idle, the voltage at the tail light is 7 volts. The tail light is definitely brighter than with the engine off ( I can actually tell it's on from a distance in the daylight). It may be good enough. The brake light is pretty darn bright, so I'm going to wire them in and see how it goes.

Thank everyone so much for your patience and advice. I feel like I've taken a course in electrical troubleshooting 101.

I skimmed the posts really quickly but I think I did something noone else here has done or at least said...I ground my '49 3100 box, cab, engine individually to the frame, battery to the starter/bellhousing bolt. Somone wiser than I said that you can't have too many grounds.

A lot of this lost voltage can be prevented by soldering all your connections.