Hi guys,

Truck in question is 78 F-150, 351M, C-6, 4x4.

I drove the truck yesterday and everything was fine that I remember.

Got up early this morning to take a bud to the airport, went by his house and picked him up, and between his place and the airport I noticed that the dash lights were a little dim. Couldn't really tell on the headlights with so many streetlights on. Dropped the guy off at the airport and went to the base. Getting off the highway I noticed that the truck was running really rough, especially at idle at a stop light. Also noticed that my turn signal lights weren't working anymore, outside or on the dash. So I have some kind of electrical problem. While sitting at the stop light I turned off the headlights and the engine smoothed out and the turn signals worked again. Now I'm thinking it’s a power supply issue, either the alternator or the battery. Since the truck actually runs off the alternator while driving, it shouldn't be the battery, but then I did not have an alternator light. I will have to check to see what actually triggers the alternator light, ie, a specific low voltage or none at all. Might be something related to the voltage regulator but not sure. Anyhow, I end up driving the rest of the way to base with no headlights because the engine was too rough with them on, luckily the gate guard didn't notice and I made it in to work ok. Interestingly the seat belt warning light came on a couple times (I was wearing the seat belt) as I was flicking the headlights on and off. After I shut off the truck, I tried the headlights again and got nothing. When I opened up the door, the cab light came on real dim, and then after a second brightened again. I tried the headlights again and they worked this time, but were dim still. I tried to start the truck and the starter will not engage at all. Even with dim headlights I should have some weak cranking of the starter. Solenoid wouldn't even click. BTW, the battery is a couple years old, the alternator is about 1 year old.

I'm really at a loss for what this might be.

Low power while driving = alternator, but the alternator light did not come on.
New alternator, weak charging = regulator
Weak headlights after engine is off = battery
No start (even with weak battery) = starter solenoid

If my logic is even remotely close here, I have no idea what it might be.

I am going to try the motor pool when they get in to see if I can put the battery on a charger just to rule that out, but I really don't think that is the problem.

Any help would be appreciated, I have a full days work ahead of me and only a couple breaks and lunch to figure this out.

TIA,
Sam

Edit: Also while I was at the guys house to pick him up, I plugged in my cell phone to get charged up off the cigarette lighter. After a few minutes I smelled something funny that hinted of electrical being hot, so I unplugged the cell phone and I didn't notice the smell after that. Could be coincidence or a key part of the problem. But again, if it was the cigarette lighter drawing too much power, it should have blown a fuze and not affected the ignition.

 

Sounds like the battery is OK.
I would say you have a bad:
1. Regulator or Regulator not grounded.
2. Alternator
3. No power on the Green wire with a red stripe running from the Regulator (I) to the Charge Ind. and Ignition Switch.
4. Charge Ind. Bulb burned out.

 

I'm going to put the battery on a charger for a couple hours, and if the truck will start, run it out to Autozone to test the alternator. Not sure if they can test the regulator or not, but it is a $11.99 part, and the alternator has a lifetime warranty from the zone, not that its worth much if it doesn't work, but does keep me from paying for it again.

 

Went out to pull the battery, and figured, what the heck, might as well check to see if it will start. Tried the key and it it buzzed, not enough juice to turn it over.

Took the battery to motor pool and they put it on a charger and said it was showing 10V. Not sure what you need to get it to crank over, but he said the battery was in good shape and wouldn't take too long to charge back up. I'll get it charged up and see if it will start the truck at lunch time.

 

It should startup OK and get you there.

Here is a diagram of the charging system if you need it:
http://i54.photobucket.com/albums/g9...hargeLight.jpg

 

Ok, got the battery charged, and the engine will crank. I just bumped it to make sure it would turn because I didn't want to waste the juice starting it if it won't charge.

Alt light on the dash does come on with the ignition on. Didn't actually start it, but suspect that since I didn't see it this morning, I won't see it today either. Interestingly enough, the alt light was not as bright as the brake and seatbelt warning lights, so I may not have been able to see it this morning with the power being so week and all the other lights being dimmed down due to lack of power.

Next question is, since I have a 25 minute commute, and Autozone is always packed, ie, a wait to get service, would it be better to leave the truck running or shut it off while I am inside? I happen to have two keys with me, so I can leave it running and still lock it. Plan is to ask Autozone if they have a small parking lot loaner tool (I only have my gerber multi-tool right now, worked for the batter, but probably won't do well on those alt bolts) so I can change it out right there, if not, I will have to have enough power to grab the new alt and still get home.

Edit: I should add that what really perplexed me about this is the whole alternator warning light thing. I've had alternators go out, but always knew it when the light came on.

What is the scenario the way the wiring is routed that the alternator or regulator would go out and there would be no dash indication?

 

If the battery was showing 10v, was that with a load tester? If it was just with a regular meter, then the battery has a dead cell.

If you can get it over to autozone, they can put their gizmo on the system with the truck running and tell you what's going on.

 

I'm pretty sure that was a load tester. He hooked up the cables to the posts and then pushed a button to show the voltage on it.

He did the same thing when it was charged, hooked up the cables, pushed a button and said it showed 12V charged.

 

OK, it now gets more interesting.

I went by Autozone and their tester didn't work, so I went ahead and got both a new alternator and regulator anyhow. I installed the new alternator and regulator last night and started the truck, everything seemed good.

I started the truck this morning and the alternator light came on. I popped the hood and found that a previous solderless connection had broken and I had to reconnect it. It turns out that line from the alternator to the starter relay is a fusable link. It had broken before and was now broken again. Hmm. I went ahead and reconnected it and restarted the truck. Alternator light was still on.

I went back and re-installed the old voltage regulator and the alternator light went out.

I proceeded to drive in to work with no problem, and as a last check after I parked the truck, I disconnected the negative post on the battery and the engine kept running. I then turned on the headlights to add some more draw, and the engine still kept running.

So, I'm now thinking that the 1 year old alternator was bad and that the brand new voltage regulator is junk.

I'm not sure what is up with the fusable link wire, but I'm going to look at NPD's truck catalog and see if I can get a new alternator wiring harness.

I think I'm in the clear for now, but still disturbed by the mulitude of failures in that corner of the engine bay.

 

Taking the battery cable off with the engine running is a risky thing to do. If there was something wrong with the regulator, and the alternator was charging wide open, the battery is the only thing that holds the voltage down. Taking it off with the engine running can ruin your electronics in the truck including any stereos and electronic ignitions.

You did not have any problems, but I want to try to discourage people from doing this. Taking a meter and reading the voltage at the the battery with the engine running is a much safer way.

Glad you got it fixed.