I have a 99 F150, with the 4.6, and my headlights just randomly quit. I checked all the fuses, and switched the MFS, and main headlight switch. All I have is my DRL's. I also checked for wires coming out of the plug-in on the column, but they seem good too. I'm just not sure where to go from here, any help would be greatly appreciated.

 

You'll need to use a voltmeter to actually measure (and report results).

Equipped with Autolamps or not?

Do ANY of the headlights work in any mode (high, low, flash-to-pass)?

Do the parking lamps work when the headlights are turned on?

Fuse F3 (under hood), F16, F26, and F28 (under dash) all okay?

 

The truck does not have autolamps. All fuses are ok, and no, they don't come on using any of those approaches. As far as checking for power I haven't done that yet. It just happened so I haven't had time to dig that much. Which circuits would be best to check first? Probably at my fuses?

 

Check the F3 circuit first since it supplies everything. Load side can be checked at the DB/OR wire at the headlight switch connector. It also goes to the MFS for the FTP feature.

 

So, I checked for power at F3 and there was 11.9 on dims and 9.5 on brights, not sure why there is this deviation. Also, when I drove the truck after work today, the theft light started blinking rapidly for around 10 minutes and then quit. Not sure if this and the headlights not working are related, but it kind of points towards the steering column wiring?

 

Better check your alternator....it might not be charging.

 

Alternator is charging, not sure what else to check??

 

Go back to F3 circuit. You should have full battery voltage on both sides of the fuse whether the headlights are switched on or of, low or high. Which side of the fuse did you measure, the supply or the load side?

What is the battery voltage when the engine is running?

Make certain that you are making ALL of your measurements with the negative lead of the meter connected to a good vehicle ground. Your reading is the previous post suggests a problem in the supply circuit or in the measurement technique. I'd suggest posting your actual readings rather than your interpretation of them.

 

Ok, so I tested the F3 circuit again, this time with the truck running. It measured 14.1 on the supply side 2.95 and the load side. I'm not understanding why there is power on both sides to begin with. If you could elaborate a little more on that, to give me a little more knowledge, that would be greatly appreciated.

 

If you're measuring on each side of the fuse while it is in circuit, replace the fuse. Otherwise, I need to know the exact point where you are making your low side reading (which is indicative of a high-resistance in the circuit).

 

The measurement was made with the fuse pulled. I had the meter grounded, and just touched each connection in the port with the positive lead. 14.1 on the left side and 2.95 on the right side (facing the windshield).

 

Sounds like the ground is pickiing up voltage from somewhere it shouldn't. If the fuse is pulled, there should not be any volts on the load side.

 

Keep the fuse in the circuit. It's pointless to take a voltage reading when the fuse is removed. Throw all those readings out the window as they are not useful. I told you specifically where to make the checks earlier. Use those points.

 

Haha, ok I definitely misunderstood how you wanted me to measure (that's why I was confused when said full voltage on both sides, thought you meant with fuse pulled). Anyways, if I have full voltage at the F3, then what measurement should I be getting on the load side at the switch?

 

The same as the supply (battery) within a few tenths.