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hey all! I've been having some issues lately. When driving, I notice my headlights, whether low or high beams, and my dash cluster lights dim intermittently. Sometimes for a just a couple seconds, sometimes up to 30. Bulbs, connectors, alternator, and battery are all new. What should I be checking next?? **edit** its the 4.6, if it matters
Last edited by ex_13Bravo; Feb 18, 2023 at 03:18 PM.
Reason: additional information
I meant the key fob used to unlock the doors. If you don't have one, that eliminates the Body Control Module as a possible cause.
The two photos are from the 2004 Ford Wiring Diagrams manual.
Referring to the wiring diagrams, since each headlight has a separate ground, I think the problem must be with the power (12v). And I think that since the low beam power to the headlights is coming from two separate fuses, fuse 23 and 25, I don't think the problem is between those fuses and the lights.
So, I'd focus on the components and wiring on page 85--1. Are you comfortable with using a voltmeter? How about jumpering wiring connectors?
I meant the key fob used to unlock the doors. If you don't have one, that eliminates the Body Control Module as a possible cause.
The two photos are from the 2004 Ford Wiring Diagrams manual.
Referring to the wiring diagrams, since each headlight has a separate ground, I think the problem must be with the power (12v). And I think that since the low beam power to the headlights is coming from two separate fuses, fuse 23 and 25, I don't think the problem is between those fuses and the lights.
So, I'd focus on the components and wiring on page 85--1. Are you comfortable with using a voltmeter? How about jumpering wiring connectors?
Voltmeter I can handle. With specific direction I'm sure I could jumper some connectors. Btw, I appreciate the assistance!!
Okay then let's see if we can figure this out. Keep in mind I'm basing my suggestions on the 2004 Ford Wiring Diagrams and there could be some differences with your truck’s wiring. Also, it seems highly likely to me that the cause is probably due to poor contact at a wire connector, thus creating excess resistance.
After examining the wiring diagrams, I would begin testing at the Main Light Switch (MLS) because that seems easiest. So you’ll need to pry out the MLS plastic cover. Then you should see a gray connector. First, remove it and plug it back in a few times because it may just be that one or more terminal connections is not making good contact. See if that solves the problem.
If not, remove it again and check for voltage at the DB/OG wire terminal 8. Should be battery voltage. Next check resistance between the RD/YE wire, terminal 9 and ground. Resistance should be very low,. I'd expect 1 or 2 ohms. If it's like 500 ohms then there's a problem further down the circuit that's likely causing the problem.
f both the tests are as expected, jumper the two wires. If the problem still exists, the MLS is good. If the problem goes away, it’s likely a faulty MLS. But to prove it, set the meter to 12v DC, plug the connector back in, and backprobe these two terminals. This will show the voltage drop. If it's more than a half a volt the DLS has too much resistance. But make sure the terminals are making good contact with the switch.
If you're unfamiliar with backprobing, you can stick a needle into the back of each wire, while they’re connected to the switch, and the lights are on, then touch the needles with the voltmeter probes.
Let’s stop there for now and see what you find out.
Before focusing exclusively on the lighting circuit, it would be a very good idea to see if the alternator's output voltage is "sagging" when the lighting dims. It's quite possible that there is an issue in the voltage regulator circuit that is causing the lighting issue, a not uncommon issue on other Fords.
Easiest method is to get one of those voltmeters that plug into the cigar lighter and continuously display the voltage available at that port, a good proxy for the battery voltage most of the time.
I agree with projectSHO89. I'd test for dips in battery voltage first.
Does it also do it at idle? If so you can connect a voltmeter to the battery terminals and watch for dips in voltage there. Also make sure the battery connections are tight.
Another thing that's easy to check is a corroded ground at the inside fuse panel.
Do you have an OBD tool. If so does it show any fault codes? Does it read live data? If so you could monitor battery voltage while driving.
