2005 Mustang 4.0 electrical problem

" dim headlights "? None of your lights should be 'dim'. You have 4 lights.

Side Lights.
Daytime Running Lights (DRL)
Low Beam Headlights.
High Beam Headlights.

Here are the fuses, check fuse 5 and D although they covers more items than lights. Your best bet is to find a good local auto-electrician.

1994-1998 Ford Mustang Fuse Box Diagram

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17 Oct 2019 - Fuse Panel Diagram Ford Mustang Mk.4 engine: 3.8L, 4.6L, 4.9L, 5.0L and 5.8L (1994, 1995, 1996, 1997, 1998)

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It sounds like a possible problem with you alternator not providing enough volts/amps to keep the lights steady. If it one light, it could be the bulb going out - buy a bulb from your local auto shop and try that. If it is both lights, you should have your alternator and battery checked at a Toyota dealer, local repair shop or if your handy with tools and don;t mind the work, pull them out yourself and take them to a local autoparts shop where they can test them for free. If either fail the test, replace them.

It is the headlight aduster. I had a call from my dealer saying there is a recall on them, they sometimes re-adjust themselves which is the buzzing you can hear. Pop into the local Hyundai dealer & they can sort it out in about 10mins.

If your plow is electric/hydraulic then you will have to introduce a second battery into the system and upgrade your alternator to a heavier one. The good news is that GM has the battery kit, it can be found in any diesel truck in a salvage yard or ordered from the dealer. Upgrade your alternator to at least a 70 amp output. If you have a local battery and electric shop they can upgrade your current alternator for a lot less than buying a new or rebuilt one. Hope this helps.

SOUND LIKE ALTERNATOR DEFECTIVE.ITS NOT KEEPING BATTERY CHARGED.

Take the alternator out and bring it to an alternator shop or electric shop to have it tested. They can confirm by testing the alternator with bench electric equipment if it is actually working. It is possible to swap out the alternator with an alternate OR have the alternator rebuilt for a nominal fee.

2005 Ford Mustang 4.0L SFI SOHC 6cyl
Ford Mustang 1999-2005
Alternator - Removal & Installation

3.8L And 4.0L Engines

1. Before servicing the vehicle, refer to the precautions at the beginning of this section.
2. Disconnect the negative battery cable.
3. Remove the accessory drive belt.
4. Disconnect the alternator electrical connectors.
5. Remove the alternator shield (4.0L engine).
6. Remove the alternator mounting bolts.
7. Remove the alternator from the vehicle.
8. Installation is the reverse of the removal procedure.

To install:

1. Position the alternator onto engine. Tighten the lower bolt to 35 ft. lbs. (47 Nm) and the upper bolt to 18 ft. lbs. (25 Nm).
2. Install the alternator shield (4.0L engine).
3. Connect the alternator electrical connectors.
4. Install the accessory drive belt.
5. Connect the negative battery cable.

4.6L Engines (Non-Supercharged)

1. Before servicing the vehicle, refer to the precautions at the beginning of this section.
2. Disconnect the negative battery cable.
3. Remove the air intake scoop bracket, if equipped.
4. Remove the accessory drive belt.
5. Remove the upper alternator bracket.
6. Disconnect the alternator electrical connectors.
7. Remove the alternator bolts.
8. Remove the alternator from the vehicle.
9. Installation is the reverse of the removal procedure.

To install:

1. Position the alternator onto engine. Tighten the mounting bolts to 18 ft. lbs. (25 Nm).
2. Connect the alternator electrical connectors.
3. Install the upper alternator bracket. Tighten the bolts to 89 inch lbs. (10 Nm).
4. Install the accessory drive belt.
5. Install the air intake scoop bracket, if equipped.
6. Connect the negative battery cable.

4.6L Engines (Supercharged)

1. Before servicing the vehicle, refer to the precautions at the beginning of this section.
2. Disconnect the negative battery cable.
3. Remove the accessory drive belt.
4. Raise the vehicle.
5. Disconnect the alternator electrical connectors.
6. Remove the alternator bolts.
7. Remove the alternator from the vehicle.
8. Installation is the reverse of the removal procedure.

To install:

1. Position the alternator onto engine. Tighten the lower bolt to 18 ft. lbs. (25 Nm) and the upper bolt to 37 ft. lbs. (50 Nm).
2. Connect the alternator electrical connectors.
3. Lower the vehicle.
4. Install the accessory drive belt.
5. Connect the negative battery cable.
6. Installation is the reverse of the removal procedure.

More details about this model in Autozone.com (free register).

I hope help you with this (remember rated this help). Good luck.

A loud whining noise under load would generally point to an alternator with either bad bearings or internal issues. Alternators are rebuildable and can be tested on the vehicle by a good rebuild shop. You can do an overhaul yourself but suggest you have it properly tested at a shop. Even a drop in exchange /rebuilt unit should save you 30%.
If the internal electronics in the alternator are problematic they could cook your battery if left unchecked

Its your headlight switch... I have the same problem with my mustang.... After time goes on it wears on the copper connectors on the headlight switch and they will either get loose or they will bend and at times losing connections... I picked up the headlight switch from Auto Zone for $16.99... AND I believe that the sound you're hearing isn't coming form your engine but its coming from the headlight switch... Dont quote me on it but I am sure thats where its coming from... Due losing and gaining connection...

The only other thing may be the voltage regulator, is this actually an alternator or a generator?