I recently built a flatbed for my 88 f150.

The factory tail lights were deleted.

I utilized the factory taillight plug and factory wiring for both left and right.

I bought and installed LED taillight, turn , stop and running. 3 wire.

Also LED reverse lights.

So after determining what was what for the wiring and grinding off to bare metal on frame installed studs for good grounds.

Everything works expect the taillight are on dim when truck running ( no headlights on ). Again all worked so I went with it for past few months.

The other day the left turn signal stopped working.

Ive dug into what I've done for wiring and all seems correct.
12 volt tester confirms power from correct wire.

Today I wired up an old bulb style taillight to see if that works. Well it does... Try the LED and no go.

I go get another from the store as I thought I had a dud. Does not work either.

Right signal is fine.




One thing to mention is that when I did original wire up to the factory plug there were 2 wires laying beside the plug.

These wires are hot when lights are on. I assumed I could just use those for marker lights etc.

 

The cause for your LED lighting up without the lights being on is LED's are very low resistance, incandescent bulbs depend on the resistance of the filament to light, If your headlight switch is getting worn it may be that a tiny bit of current is always applied to the light circuit, the resistance in the incandescent filament will bring it down to 0 volts and the light will not shine until the switch is engaged (in these trucks all the amperage (current) is ran through the headlight switch) With LED's as they are very low resistance they will glow dimly unless there is enough resistance to pull it down.

If you have a regular bi-metal turn signal flasher, that too depends on resistance to work. With those there are two pieces of metal inside that are made of different types of metal, as current (amperage) flows thru them when they are closed, one heats up a tiny bit causing it to bend and it opens the circuit,Your light is then off, when it cools it closes the circuit and your light is on.If there is not enough current draw the light will either stay on and not flash when activated or will hyper flash .They make a direct fit electronic flasher that resolves that.

SOME LED bulbs are polarized, meaning they will only work one way in the socket, usually the fix for that is to flip the bulb 180 degrees.

My 93 has an E4OD tranny, it does not play well with LED's on all 4 corners as it gets it's torque converter unlock signal from the brake lights. I had tried putting resistors in line to add the needed resistance to the circuit but it turned out to be more of a pain in the neck than it was worth.

Every thing is LED on my truck for exterior lights except the Headlamps / tail / brake lights and I changed to an electronic flasher and it works just fine.

 

Thank you for reply Z
So if I understand I can change my flasher ? That may resolve light being on.
Flasher being the signal flasher ?
I believe my new lights are labeled top and that is the way they are installed.
A new headlight switch may be the answer ?

 

Also, don't forget that you can have voltage without current (as above, a faulty switch or any bad connection including grounds could impede current flow).

Example.... Years ago I was installing some Alley Lights on a police light bar and couldn't get the halogens to light. Meter showed 12v at the socket. Turned out that the 12v feed for the lights was fine but the ground was bad. I figured this out by using a jumper direct back to battery neg and got the light to work. I ended up pulling a dedicated ground for the alley lights.

If you are using the frame as your ground return, check the bonding straps from the frame back to the engine/battery.

A dedicated ground wire is always the best way to go.

TG

 

I would replace the headlight switch to eliminate that as an issue. and the flasher is the signal flasher ,correct. You would want an electronic one if you are intent on running LEDS. This should fit, but to be sure, pull yours and cross reference the number. Electronic flashers will work with regular or LED lights. The "pig tail' is a ground.
Check your grounds as suggested and make sure you have a good ground to frame. Check the polarity of the bulbs again.

 

Okay so I phoned parts store and they want to give me same flasher as I have.

I see the one on Amazon has a ground lead out of it. So not as what I have ? I have a regular glass style flasher.
The one on Amazon is to regulate or send correct voltage to signal making an LED work ?

I ran a ground right to battery to rule that out. No change.

I get u bumm haedlight switch may "leak" power being the cause of lights on dim when they shouldn't be.

I will attend to that but that shouldn't be my turn signal problem ?

 

I did read up on style of flasher recommended , I see it is built to operate LEDs so thanks for that.

 

This is the LED-rated flasher I got for my 1995. Pinout is correct and it will fit in the round flasher spot.

FL2-RED LED Bulb Electronic Flasher

 

Tip of the hat. You know your stuff.

 

I'm an Industrial electrician and electronics experimenter Thank You.

 

Thanks folks ! I'm on it.

 

So here is what I bought. No instructions in box but assume lead is ground. Zero voltage to light, turn signal left or right does not work. Did I buy wrong one, maybe not compatable ? Bought locally.

 

may not be compatible. It can be a crap shoot finding one that works right. If you haven't gotten it fixed by tomorrow night I will pull mine and take a pic of it. Make sure the ground on the flasher is on a good ground location. I grounded my block to body, body to frame, bed to frame,etc.. made sure I had good grounds all the way through for my radio equipment and antenna grounding.

 

I ran a ground right to battery just to check but no go.
Definitly no power coming out of leads to tail lights.
Thanks for the help !

 

I've ordered the one you posted a link to on Amazon .
Should see it in a few days and hope it works.
will update.
tx