I have an 89' f-150 with a 300 I-6. When I am driving at night and come to a stop or push the clutch in so the motor idles, the headlights get dim. If I "rev" the engine up in neutral they stay dim, but if I engage the clutch and start moving, they get bright again. I also notice some other weird stuff like when I plug in a phone charger to the cig. lighter all of the electrical seems to go dead for a second and my turn signal flashers flash very slow. Also sometimes when I have been driving aroud town for a while and go to start it, the motor cranks very slow as if the battery is low, however if I try two or three times it cranks normally. Can anyone give me any ideas? I,m not sure if this is an electrical problem, or a problem with the motor/drive train.

 

Goofy electrical problems are often because of poor grounds. Check your grounds for good connections from the battery negative to the engine block and to the chassis and sheet metal.

 

If the lights dim with the clutch pressed I would look at the clutch safety switch or the starter relay!

Do the lights stay dim with the truck in neutral and clutch not pressed?
That would lead me to think relay or safety switch!

 

I am currently fighting one of these oddities, for the last three weeks my oil pressure has been lower then normal, and my voltage has always been let's just say, strange. Dim lights, slow fans, all that jazz at idle. I replaced the alternator, slight diffrence still low oil pressure. I cleaned up the chassis ground, the oil pressure returns to normal, but dimming still occurs. I'm getting new battery and ground cables to see if that will completely solve the issue.

 

The lights stay dim if in neutral and the clutch is out. They only get brighter if I am going down the road. I will check the grounds and battery connections, Where might the ground from the frame to the chassis be? I also noticed this morning that my windshiel wipers are slow when the truck is idling, but get faster when I am driving.

 

I am currently having the same problem with my dads car (mitsubishi galant 2.0 DOHC) I will notice that the lights seem to brighten, and the wipers speed up only when the cluch is engaged, and the car is moving. But if you rev the engine for a few minutes everything speeds up, and brightens. I say check and clean your grounds. but it is probably the brushes in the alternator are getting won out. fix thoes and the problem should go away
But also check and clean your battery posts and cables.

 

The one thing that is overlooked by almost everyone who owns a FORD TRUCK is the MIDDLE LENGTH CLAMP/GROUND on the Negative cable. This clamp is bolted to the top of the frame directly below the battery and CAN/WILL corrode faster than any other connection due to it's location. You won't see the corrosion. REPLACE THE CABLE with two separate ones (one to battery, and one to starter/engine).

Also inspect and clean any other body and frame grounds.

Larry

 

I cleaned the grounds that go from the frame to the wireing harness and the battery cables today. I didn,t have a chance to get to the "Middle length battery cable" but it does look like it needs replaced so I will try that tomorrow. I drove the truck tonight and it didn't seem to make much differance. I also did a little more symptom checking and found that when the truck is idling eith the headlights on, the voltage drops to about 9 volts with the clutch in, if the clutch is out, it's not as bad. If I have the truck idling in neutral and push in and out on the clutch the voltage goes up and down a lot. Does this sound like a ground thing or do I have a problem with the neutral safety switch or alternator?

 

Pushing the clutch in should increase the idle, even in neutral, as the engine is no longer spinning the transmission at this point. I'd lay odds on dirty connections mostly. If you can find it, try unplugging your neutral saftey switch, and give both the plug and receptical a good bath in WD-40 and plug it in and unplug it several times to remove the "green disease" type corrosion it's likely to have. Also do the same to your alternator plug(white plug that connects it to everything else) Replacing all three battery cables(BATT +, BATT -, and solenoid to starter) will help. Fresh metal and a good cleaning to the secondary ground won't hurt either. There are also ground wires for every other electrical device on the truck, and cleaning the contact points will help as well. Over time they all get rusty. Everything from the light to ground for your tail lights, headlights, marker lights, wipers, heater fan, a/c unit....the list goes on...if it's electrical, it has a grounding point somewhere. Each and every one of them will contribute to this issue, especially the ones exposed to the elements outside of the cab.

 

At this point I would think the Alternator or voltage regulator is bad!

 

I think I will take it to Autozone and see if they will test the alternator. Where is the voltage regulator located? Also, I said neutral safety switch in my previous post, when I should have said clutch safety switch since my truck has a four speed. It is my understanding that it is not located in the charging system, but could it cause the problem? Thanks for all your help so far.

 

Alternator and battery checked out fine. I guess I will work on the grounds some more unless anyone has any other ideas.

 

Clutch safety switch, if your truck is so equipped is likely mounted under the dash, and is in the closed state with the clutch depressed, to allow starting. If your truck can start in neutral, with the clutch released, you either don't have one, or it's not working. Some standards also come with the neutral safety switch, which is on the transmission. This switch also activates your back-up lights, as a general rule of thumb. Check and make sure your engine block(near the fire-wall) has a block to ground on body strap(wire) it's usually a braided silver colored wire. I've seen many trucks without this, and it's not being there will cause all kinds of grief. You can substitute any piece of at least 10 guage wire in it's place if need be, or a short peice of battery cable if you really want to make sure it works good. Just make sure the block is grounded back to the body. Other than that, how long has it been since you changed your battery cables? They do corrode inside the coating after a few years of use, and corrosion creates resistance, which will also cause your problems. Green disease, as I refer to it(copper turns green when corroded) will create all kinds of hedaches as well, including hot start problems.(makes the starter drag, or not turn at all)

 

Thanks RR4E, I will check the ground your talking about. I almost think it has to be a ground problem since it affects so many differant things. The negative battey cable that runs from the battery to the frame and then to the starter bolt is the next thing I will replace. It looks a little corroded where it attaches to the frame. Do you think this could cause the problem?

 

It can, any corrosion will cause some problems in regards to ground wires and hot wires as well. electical ghosts are tough to trace....pick on the obvious first.