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Flareside Tail lights not working

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Narlin_B

Flareside Tail lights not working

I'm having an issue with my tail lights not coming on. The hazards and brake lights work. When the key is on, and I run the turn signal, both tail lights will flash no matter the direction. The front markers still work independently. The backup lights don't seem to work either. I have confirmed that power is getting to the harness and the bulbs are new. I also replaced the flasher on the face/driver's side of the fuse panel.

1984 F150
2wd, 300 I6, ZF-S542
Duraspark II Conversion, Aussiespeed Intake, Motorcraft 2150 Carb

Gary Lewis

Re: Flareside Tail lights not working

Administrator

Is it possible that when you said "tail lights" you mean "turn signals"? Actually, Ford calls the tail lights the "rear park lamps".

The tail lights don't have anything to do with the turn signals, as you can see below.

But if you mean the turn signals, then I think you have a bad turn signal switch. As you can see below, everything runs through that switch, and they are known to fail.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

Narlin_B

Re: Flareside Tail lights not working

The tail light function of "constant on" doesn't work when you turn the lights on. When you use the turn signal switch, both tail lights flash at the same time no matter which direction you put it in, but the front markers flash independent.

1984 F150
2wd, 300 I6, ZF-S542
Duraspark II Conversion, Aussiespeed Intake, Motorcraft 2150 Carb

Gary Lewis

Re: Flareside Tail lights not working

Administrator

Then you may have a ground problem. Everything thing in the rear grounds to a ground under the dash. But if the wire is broken or bad along the way strange things happen.

Try grounding one tail light back to the battery and see if the symptoms change.

Gary, AKA "Gary fellow": Profile

Narlin_B

Re: Flareside Tail lights not working

So take the lens off and slip a wire into the bulb socket and run it to the battery? Guess I need to go buy a roll haha

1984 F150
2wd, 300 I6, ZF-S542
Duraspark II Conversion, Aussiespeed Intake, Motorcraft 2150 Carb

Gary Lewis

Re: Flareside Tail lights not working

Administrator

You can use an extension cord. Use a short piece of wire from the battery's negative post into the ground/round hole on the female end of the extension cord, and just touch the prong of the ground on the male end to the metal on the side of the bulb - assuming it is showing a bit.

With the turn signals on one way or the other this should prove if it is a ground problem. The rear light should work properly with the ground - if it is a ground problem.

Gary, AKA "Gary fellow": Profile

Rembrant

Re: Flareside Tail lights not working

In reply to this post by Gary Lewis

Gary Lewis wrote

Then you may have a ground problem. Everything thing in the rear grounds to a ground under the dash.

Gary,

The Flareside taillights are grounded by the 3 mounting studs, so they ground to the mounting brackets, which ground to the bed, which grounds to the frame. I recall somebody saying that sometime later...maybe 85 or 86, they ran a separate ground wire to the frame, but most Flareside tailights are grounded only by the 3 mounting studs to the mounting bracket. It is a crummy ground, to say the least (imho).

On my '84, the only thing in the rear that had a factory ground wire from the front of the truck was the license plate light.

1994 F150 4x2 Flareside. 5.0 w/MAF, 4R70W, stock.
1984 F150 4X2 Flareside. Mild 302 w/ 5spd. Sold.
1980 F150 4X4 Flareside. 300i6 w/ 5spd. Sold in 2021.
1980 F100 4X2 Flareside. 351w/2bbl w/NP435. Sold in 1995

Gary Lewis

Re: Flareside Tail lights not working

Administrator

Yep, you are right. I am wrong.

Gary, AKA "Gary fellow": Profile

Narlin_B

Re: Flareside Tail lights not working

In reply to this post by Rembrant

I'll have to try adding extra ground connections back there. Going to test the turn switch some time today.

1984 F150
2wd, 300 I6, ZF-S542
Duraspark II Conversion, Aussiespeed Intake, Motorcraft 2150 Carb

FuzzFace2

Re: Flareside Tail lights not working

In reply to this post by Rembrant

I was going to say the same thing

I had to make the tail light harness from my parts truck style side harness, both trucks were 81's.
In testing after I opened the SS harness I had no lights and was like

Then it hit me I needed a ground so I hooked up a jumper wire from the harness grounds, the SS lights had a eyelet at each lights screwed to the bed, I then had lights.

Now When I rebuilt my truck the new neg. battery cable follows the factory path and (factory) it had a tab that a bolt goes thru and screws on the top of the frame rail.
My new cable I made the same way to the frame is grounded.

This Cable goes to a starter bolt to ground the motor / transmission.
I also redid the factory motor to cab firewall ground using a 10ga wire, this takes care of the cab body ground.

Now my Flare Side uses a Style Side metal ribbed floor not wood like the factory did and I don't have any tail light issues from day 1.
I would add a bed ground say from 1 of the bed side to the front panel bolts on the under side to the frame.
I would also check the battery to frame & motor ground to make sure they are good.
This way when you add the bed to frame ground it will work.
Dave ----

Dave G.
81 F100 flare side 300 six / AA OD / NP435 / 2.75 gear
http://cars.grantskingdom1.com/index.php/1980-Ford-F100?page=1
81 F100 style side 300 six/SROD parts truck -RIP
http://cars.grantskingdom1.com/index.php/1981-Ford-F100

Narlin_B

Re: Flareside Tail lights not working

In reply to this post by Narlin_B

Well I added a ground wire into the mounting bracket for the tail lights and ran it to the frame. They work now. Thanks for the help

1984 F150
2wd, 300 I6, ZF-S542
Duraspark II Conversion, Aussiespeed Intake, Motorcraft 2150 Carb

Gary Lewis

Re: Flareside Tail lights not working

Administrator

Excellent!

Gary, AKA "Gary fellow": Profile

Rembrant

Re: Flareside Tail lights not working

In reply to this post by Narlin_B

Excellent! I added a wire to mine also, when I rebuilt the bed and installed new lights. The factory grounding method was sketchy at best in my opinion lol. I believe some of the later models had a wired ground, but it’s not common.