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Tail Lights Acting Up

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Tail Lights Acting Up

I have a 1980 F100 Custom 6 Cylinder. I have just gotten it running and on my first drive, I noticed that my tail lights and turn signals were working off and on. Sometimes one would work, sometimes the other, sometimes none would work, sometimes all would work. Also, the temp and fuel gauge was not working. I have just replaced my sender and thermostat so I know they are working fine and those gauges both work normally (it was just this one time they didn't work). I've read where the starter switch could go bad causing the gauges to not work. I have ordered a new starter switch and will replace this weekend. Would the starter switch also affect the tail lights? Any ideas where I should start looking? I was going to start with replacing all the wiring to the sockets and go from there.

1980 F100 Custom. Inline 6. Power steering. 3 on the Column.

Gary Lewis

Re: Tail Lights Acting Up

Administrator

Let's be more specific - the ignition switch can cause similar problems. I just want to be clear so someone doesn't think we are talking about the starter relay, aka the starter solenoid.

And the issue is that there are 6 contacts in the ignition switch that all make/break at different times. It seems that the ignition circuit itself is very forgiving, but the accessories contacts are persnickety and the key has to be in just the right place.

And the ignition switch can cause issues with the turn signals. But not the tail lights as they are powered via the headlight switch.

The early Bullnose trucks used the bed for a ground to the rear lights, and that ground was frequently a problem. And people hacking the light wiring to add trailer connectors made it even worse. So I'd check the ground, which is found after pulling the tail light housing out. And I'd check the wiring where it might have been hacked down close to a trailer hitch.

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

Powerman5K

Re: Tail Lights Acting Up

Sorry, yes the ignition switch. I will start with the ignition switch and go from there. It has only done it once to me and it was all at the same time. I'm hoping the switch does the trick as I'd rather not run all new wiring if I don't have to. When I said tail lights, I misspoke. I meant to say brake lights (not tail lights). Would break lights be affected by the ignition switch too?

1980 F100 Custom. Inline 6. Power steering. 3 on the Column.

Gary Lewis

Re: Tail Lights Acting Up

Administrator

No, brake lights are hot all the time and are only controlled by the brake light switch on the brake pedal.

And on the ignition switch, you can usually turn the key back just a bit and get everything to come on if that is the problem. And look at the instructions on true Ignition Switch tab on the page at Documentation/Electrical/Ignition for installation.

Gary, AKA "Gary fellow": Profile

Powerman5K

Re: Tail Lights Acting Up

Will do. Thanks!

1980 F100 Custom. Inline 6. Power steering. 3 on the Column.

Littlebeefy

Re: Tail Lights Acting Up

Do you have a little computer behind your dash? Don't the rear lights route through there? I want to say that there is a connection behind the dash above the driver's right knee that lighting runs through which can get corroded and show "inconsistent" connection. Am I making this up Gary? I feel like this is a problem I dealt with on my 84 with CC.

LittleBeefy aka Chad

“Dot Doitall”: 1984 Bronco XLT
460 (C8VE), Edelbrock Pro-Flo 4, ZF5, NP205, D44HP solid axle, 4.56
urban assault vehicle

"Bebe": 2022 Bronco Badlands 2dr
2.7l, Sasquatch, Iconic Silver, Black Marine-grade interior, hard-top

"Celeste": 1979 Porsche 928
4.5l K-jet, 5-sp, S4/GTS brakes, LSD, Pasha interior

Gary Lewis

Re: Tail Lights Acting Up

Administrator

Chad - There is a ground on the firewall that the lights do use, and it can certainly do this. I'd say it is to the left of the radio and to the right of the throttle pedal, and it may well be the problem.

Gary, AKA "Gary fellow": Profile

Littlebeefy

Re: Tail Lights Acting Up

Hi Gary,
I was actually thinking about the 11 pin connector behind there. I looked it up on the EVTM and it's c306 on the 81 and c305 on the 85. The brake lights run through this connection and it's a possible source of disconnection (corrosion, loose, broken, etc). I have a CC and the brake lights run through the CC computer at C305A (for some odd reason) and I had problems there. Worth checking the connection if cleaning the ground doesn't help.

Powerman5K

Re: Tail Lights Acting Up

I'll start with the ground wire then move on to the other connections if that doesn't solve it.

1980 F100 Custom. Inline 6. Power steering. 3 on the Column.