Well, i recently developed a problem with my 2000 ford f150 4.6l. I was on my way to the local rink when i went to turn right and i got the fast flasher, so i figured bad bulb, my front signal light worked so i replaced the rear one. Still happens. The brake light doesn't work at all on that side, but the running light does. When i unlock/lock the lights flash light normal. So i checked the fuse that could be possibly be the culprit, but all the fuses were good. I crawled underneath and looked at the wiring due to the fact that i have a tailgate light bar and a trailer wire harness that t-harnesses into the factory wiring plug. One exactly like this..



So i checked that, but it looked good, and the ground i also checked and re-scraped it..i don't know what else to do, and any suggestions would be greatly appreciated! Also i just installed my new alternator the night before, and i have been driving around in very wet and slushy roads.

-Thanks!

 

If I'm not mistaken, the lock / unlock flashes the parking lights - not the brake / directionals. So you might be looking at the other filament illuminating. The first thing I'd check is if you actually have power at the socket. The second thing I'd check is continuity at the bulb. (Yes, I actually did manage to purchase a "pre-burned out" bulb once.) If you have a good bulb and no power, I'd be looking for a broken wire next.

 

It does flash the parking lights, and i have tested the bulb on the bench with a 1 amp battery charger, and i did test both filaments. And i have tested power at the plug, i do think its getting power, but i did test the harness and not the socket. There is three wires at the harness, and at one point i had .25 volts between two of the wires (not sure which ones). But i have not tested the socket. Is there any diagrams or ways to go about that?

-Thanks

 

The three wires should be one hot for the parking light, one hot for the brake / directional and one ground. Obviously, you should have 12 volts (with the vehicle shut off) to either of the hots with the appropriate circuit energized. If you're only getting one quarter of a volt, you have issues.

BTW, I'd be real tempted to pull that trailer harness out just to see if that might be part of the problem.

 

do you know which wires are which? i think one is red and two are black. And i just tried that trailer plug and its fine.

 

Only 1 should be black ( ground ).

The other 2 :

Brown = parking lamp circuit.

3rd wire is the stop / turn circuit ( different color on each side of the truck ).

Think rear right side is orange w/ light blue stripe..

 

Thanks guys. Im going to try some other things and get back to you. Everyone ive talked too said it must be the bulb, and maybe i did buy a pre-burned out one. My other thoughts would be The actual connector and im going to check some more grounds. Man, ive had some bad luck with my truck lately. First starter solenoid, then battery, then alternator. Hopefully this isn't as expensive as those other things. I replaced all those things in the past week.

 

How can the bulb be burnt out when you tested it as working on a battery charger ?

When you checked with a meter at the bulb connector, did you get power ?
- check using the bulb connector ground as well as another known ground on the truck, the reading should be the same +VDC as the battery.