Can I make trailer signals brighter?

[Libbs]

Hi guys.

When I tow my boat in daylight, the signals on the trailer are barely visible. When I turn my running lights on, all the lights are clearly visible, but the signals are still low.

Using a voltmeter (set at 10V scale), I determined that the connection at my vehicle's plug is dishing out 10+ (off the scale) volts to my nice, normal, bright, easily visible trailer running lights. However, the voltages for both left and right signals top out at about 5.5 volts. I tested the voltage at my trailer lights and an still getting about 5.25ish volts, so not much loss. Inside the vehicle, I tested upstream from where my wiring harness is coupled, and same, my vehicle only dishes out a max of 5.5 volts to both left and right signal lights.

The vehicle is a 1999 Jeep Cherokee Sport. Is it normal for signal voltages to be half or less than the voltage sent to running lights? The vehicle's signal brightness seems normal at this voltage. But the trailer lights barely show the signal.

What should I check? Is there a way to increase the voltage that the vehicle sends out to signal lights?

Thanks so much.

Libbs

 

[04fxdwgi]

Re: Can I make trailer signals brighter?

Hi guys.

When I tow my boat in daylight, the signals on the trailer are barely visible. When I turn my running lights on, all the lights are clearly visible, but the signals are still low.

Using a voltmeter (set at 10V scale), I determined that the connection at my vehicle's plug is dishing out 10+ (off the scale) volts to my nice, normal, bright, easily visible trailer running lights. However, the voltages for both left and right signals top out at about 5.5 volts. I tested the voltage at my trailer lights and an still getting about 5.25ish volts, so not much loss. Inside the vehicle, I tested upstream from where my wiring harness is coupled, and same, my vehicle only dishes out a max of 5.5 volts to both left and right signal lights.

The vehicle is a 1999 Jeep Cherokee Sport. Is it normal for signal voltages to be half or less than the voltage sent to running lights? The vehicle's signal brightness seems normal at this voltage. But the trailer lights barely show the signal.

What should I check? Is there a way to increase the voltage that the vehicle sends out to signal lights?

Thanks so much.

Libbs

If you are getting full 12 VDC w/ just the running lights on, then drops to 5 VDC, you have a bad ground somewhere. At the connection to the tow vehicle, at the connection to the trailer, at the lights themselves or possibly some incorrect wiring. When you see a drop like that, it usually indicates that the turn signal bulb filiment is using the running light bulb filiment as a current path to ground also, in series, effectively doubling the resistance of the circuit and dropping the voltage.

You should have full battery voltage at each light connection, when applied. Checking / cleaning / re-connecting all the grounds is where I would start. Been down that road sooooooo many times.

 

[T_Herrod]

Re: Can I make trailer signals brighter?

An easy way to tell if you have a ground issue is to turn on your lights and a turn signal. Look closely at the running lights and see if you can see a very slight flashing action in them. Or turn on the hazard flashers and see the they alternate instead of flashing togeather.

 

[MH Hawker]

Re: Can I make trailer signals brighter?

ok is it wired on the tow truck with a T connector or just tapped into the harness, right off hand I would suspect the running light and the turn signal wires are reversed on the stop/turn signal lights. The running light should be wired to the dimmer element.

 

[Chip Chester]

Re: Can I make trailer signals brighter?

Good recommendations above. Also, set your voltmeter to the next higher scale. 10+ volts could mean 10.2, instead of 13.8 ish when running. Separate ground is a must -- not thru the hitch ball. Clean all connections, verify the correct filament is in use as mentioned above... or switch to LEDs everywhere. Very bright, and lower current draw makes the most of your stock wiring and whatever voltage makes it back there.

(I've always wondered why trailer connector mfg's don't make gold-flashed connectors for this stuff. Audio connectors have had this for better than 20 years, so it's not out-of-this-world expensive. )

Also, always check all of them before you get underway. The boat you save may be your own.


Chip

 

[UncleWillie]

Re: Can I make trailer signals brighter?

... I've always wondered why trailer connector mfg's don't make gold-flashed connectors for this stuff. Audio connectors have had this for better than 20 years,...

Without getting into the marketing side if the gold connector debate...

Audio connector tend to be a plug it in once affair.
Trailer connectors tend to be a daily use item.
The Gold flash would be gone in a flash at the spots that rub together everytime the plug goes in and out.
95% of the connector would still look great, but the 5% that actually makes contact would be back to Tin on Tin after the second day.

A little grease is very functional.

 

[BRICH1260]

Re: Can I make trailer signals brighter?

Sounds like you have some electrical issues that need to be addressed first,, but I have also found that lining the housing with aluminum foil or spray painting the inside silver does help a little reflecting more light through the red lens.

 

[Chip Chester]

Re: Can I make trailer signals brighter?

UncleWillie wrote: "Trailer connectors tend to be a daily use item."
Life would be grand indeed if daily boating were part of it...

Grease is the key, for sure, but for the world of once-a-month boaters, corrosion rears its ugly head before wear does. (And curiously, my actual-daily-use gold-plated contacts -- on headphones -- survive many years without visible wear.)

It's just something I pondered during the annual burnishing of my late father's car and boat connectors...
And I, too, will stay well away from audiophile marketing-speak. Those guys are even more nuts than sail... er, well, let's just not go there at all!

Chip
(kidding, kidding)

 

[UncleWillie]

Re: Can I make trailer signals brighter?

... Inside the vehicle, I tested upstream from where my wiring harness is coupled, and same, my vehicle only dishes out a max of 5.5 volts to both left and right signal lights.

If you have the factory tow electronics. Check the fuses. There are more than one!

If a tow converter is installed, may be a Converter/Wiring issue.
Ususally located behind the drivers side tail light assembly.

 

[Silvertip]

Re: Can I make trailer signals brighter?

If the running lights are bright you can draw two conclusions and only one solution.

1) Ground for the trailer is good. Both running and tun/stop lights would be dim if that were not the case.
2) Having brighter running lights than turn/stop means the circuits are reversed. Brown is the running lights. Yellow and green are the stop/turn. This means the wiring at the stop/tail/turn lamps is reversed. If the wires were actually switched in the harness the marker lights would blink and would not be on unless the brake lights were on. The

The solution is to verify that the trailer harness on the truck is providing the proper signals to the trailer (on the proper pins). Then verify that the wiring indicated in #2 above is correct for the trailer. The best way to test the trailer is with your battery charger. Connect the NEG lead to the trailer frame. Clip a nain into the POS clip and tough each pin to verify operation of that circuit.

 

[bruceb58]

Re: Can I make trailer signals brighter?

Your vehicle has an issue somewhere if you are measuring 5V on the vehicle side.

Need to consult a factory manual and double check all your vehicle's connectors in the circuit path.

 

[dmccaffrey]

Re: Can I make trailer signals brighter?

This is easy to fix.

You need to replace your turn signal module with a heavy duty model. This will make both the turn and brake lights as bright as they should be. I know it doesn't make sense but trust me ... I had this same problem with my Jeep.

 

[Libbs]

Re: Can I make trailer signals brighter?

Wow thanks for the many replies...you guys rock. Lots of good information here.

Just to answer a couple things and clarify:

-My voltmeter is not digital unfortunately, and the next selection on the scale is 250v, so the needle would barely move. Thats why I'm kinda stuck at a 10v scale unless I go buy another...
-The voltage does not "drop" when the running lights are turned on...the signals always top out at 5.5v, running lights on OR off.
-The wiring harness is a "T" harness that simply plugs-in near driver's side tail-lights. I tested the wires leading into the harmess. The same numbers show up there (well over 10v for running lights, only 5.5ish for both signals.)
-I know the wiring is not crossed or reversed because the colors are correct, and this 5.5v is actually the high end of the oscillating (blinking) voltage, as I was testing with hazard signals turned on. Brown=steady 10+v when running lights on, yellow and green oscillating to 2 to 5.5v with the blinking.


So...

04fxdwgi stated above (post #2) that "You should have full battery voltage at each light connection..." If this statement is correct, the problem is upstream of everything I have checked so far. The voltage from the signal wires going into the harness "T" connection are only 5.5v. This is all the vehicle sending. Including to it's own tail signals, which appear fine in brightness. If I am indeed supposed to be getting a full 12v on the signals, I might have to dig a little deeper...

 

[NYBo]

Re: Can I make trailer signals brighter?

I believe your Jeep uses separate brake and turn signal bulbs. If so, that means there has to be a converter between the Jeep and the trailer. It will be a small box that part of the wiring harness that has the tee connector. The converter my be bad.

 

[superbenk]

Re: Can I make trailer signals brighter?

Have you considered LEDs? Longer lasting, WAY brighter, less power draw requirement, don't have problems with bulbs popping when they hit cold water, etc.

I got my set of tail lights for the trailer from the local auto store for about $30-40.

 

[CoffeeHound]

Re: Can I make trailer signals brighter?

Jeep uses 3157 tail light bulbs -- requiring 12vdc -- if they are working on the jeep properly and OP has junctioned to that harnnes, it would stand to reason that he has 12 vdc at his meter ---not 5.5vdc . I am assuming this is the case and could be all out in right field. Or he has a crapped out meter and needs o get a test light !!

 

[GA_Boater]

Re: Can I make trailer signals brighter?

Your meter may be giving you erroneous readings. It may not be able to react fast enough to the flashing on/off voltage. One or two things to try, have some hold the brake pedal down or put a brick/weight on the pedal. Then see if you have a steady 12V. If you don't, backtrack to the convertor and check the input, again looking for 12 volts. If the convertor has 12v in and 5v out, it's bad. If you do have 12v with the brake held at the trailer plug, look into LEDs or a new set of lights.

BTW - both running and brake/signal lights use 12 volt. The intensity is controlled by the bulb filaments, not voltage if the volts are the same for both circuits.

 

[Jlawsen]

Re: Can I make trailer signals brighter?

Well, you can always just run 6v bulbs provided it's not on the same circuit as the brakes.

O.K. I was just trying to be funny.. You're seing 5.5v approx because your meter can't react fast enough to go from 0-12 and 12-0 so it's getting an average of 5.5 or so. I suspect it's a bad ground at the light fixture or maybe the wrong bulbs. But, hey, what do I know.. nuttin.

 

[UncleWillie]

Re: Can I make trailer signals brighter?

I can't find if you ever mentioned.
Did this setup ever work correctly, or is this a "New to You" trailer and you inherited the problem?

The turn signals, the brakes, and the emergency flashes are the same filament.
The Tail Light are on the other filament.
The Brakes do not flash, so have one of the kids step on the brake pedal so you can get a steady voltage reading.

While you are at it, look at the actual bulbs
The Brighter Brake/Turn filament is the Thicker one, usually closest to the socket on the outside wires.
The Dimmer Tail Light filament is the Thinner one, usually taller and on the inside wires.

Turn on the tail light Only. Then the brakes Only.
Each filament should light independently.
If they are both coming on, Ground Problem!


Two final thoughts to keep in mind...

If you have a "Powered Converter" it has it's own wire and fuse to the battery.

The converter deals with mixing the turn and brake signals together, the tail lights are not "converted", just passed through.

 

[04fxdwgi]

Re: Can I make trailer signals brighter?

Wow thanks for the many replies...you guys rock. Lots of good information here.

Just to answer a couple things and clarify:

-My voltmeter is not digital unfortunately, and the next selection on the scale is 250v, so the needle would barely move. Thats why I'm kinda stuck at a 10v scale unless I go buy another...
-The voltage does not "drop" when the running lights are turned on...the signals always top out at 5.5v, running lights on OR off.
-The wiring harness is a "T" harness that simply plugs-in near driver's side tail-lights. I tested the wires leading into the harmess. The same numbers show up there (well over 10v for running lights, only 5.5ish for both signals.)
-I know the wiring is not crossed or reversed because the colors are correct, and this 5.5v is actually the high end of the oscillating (blinking) voltage, as I was testing with hazard signals turned on. Brown=steady 10+v when running lights on, yellow and green oscillating to 2 to 5.5v with the blinking.


So...

04fxdwgi stated above (post #2) that "You should have full battery voltage at each light connection..." If this statement is correct, the problem is upstream of everything I have checked so far. The voltage from the signal wires going into the harness "T" connection are only 5.5v. This is all the vehicle sending. Including to it's own tail signals, which appear fine in brightness. If I am indeed supposed to be getting a full 12v on the signals, I might have to dig a little deeper...

As it's a '99 Jeep, I can't see any exotic wiring scheme involved. As stated in other relies, that Jeep takes a 3157 tail light bulb (from the parts list I have), which is a 12 volt bulb, and can't possibly work at full brightness on 5.5 VDC. I think there's some more checking to be done.

I would start with a meter that reads in more usable scales (or a regular old test light probe). Are you sure meter is set to DC volts and not AC volts? Had to ask. A good meter will ensure you know exactly what you are looking at. And be sure the meter negetive lead is set to a GOOD ground.

I have been working on vehicle electrical systems as a side business for 40 years and symptoms just don't make any sense at all, unless your tester is lying to you.