I posted this once before and could never really put a finger on the problem.

89' f150 4X4 with 300I6 and manual tranny. I am having some type of charging/electrical problem.

1. I started hearing an intermitant noise under the hood while driving/ideling. It sounded like an electric motor running similar to a windshield washer pump.
2. Shortly afterword the voltage gauge would drop while ideling and the clutch in. If I put the truck in neutral and let out on the clutch the voltage would come back to normal. It was not related to RPM, I could just barely push in on the clutch pedal without actually disengaging the clutch and the voltage would drop. This was also intermitent. The battery light would not come on.
3. A couple of weeks later I would notice the voltage dropping while just driving down the road. The headlights would get dim, heater blower slow down etc. however the truck would always start like the battery was fully charged.
4. Then I began to notice the battery light coming on while the voltage dropped, the voltage would also at times go way above normal and the battery light come on.
5. Today I started the truck and everything was normal for a few minuets, then I heard the "motor" noise again, the voltage dropped, battery light came on, then the voltage increased above normal and the light came on, then everything went back to normal. All of this happened at idle.

I have had the alternator checked and autozone said it was OK. I also ran all new ground wires, checked all battery connections, and any other wires I could find.

Sorry for the long post, but I thought I would describe it as best I could now. I am afraid I am going to get stranded somewhere. Does anyone have any ideas?

Thanks a lot.

 

From the symptoms you describe, I would have suspected a poor ground connection between the truck frame and the battery. If you replaced the ground wire between the battery and the engine block and any ground straps between the engine and the truck frame (body actually), you should be OK.

Your problem shows itself when you push in on the clutch? Pushing on the clutch might cause enough movement between the truck's body and the engine where a poor ground would show up. I would check and replace every ground strap that you can find. Then see how the truck runs afterwards.

Another possibility is the voltage regulator - a bad regulator would cause voltage variations and might cause some noise. I think your regulator is external to the alternator and is mounted on the passenger's side wheel well area.

Lou Braun

 

Even though your alternator checked out OK I definitely wouldn't rule it out. My 88 F-150 was acting about like that and it was the alternator.

 

I replaced all of the grounds from the battery to the frame, from the frame to the starter, then went from the starter to the firewall. I also replaced or wire brushed all other grounds that I could find. The only thing I am not sure of is where the dash actually grounds.
I thought the volltage regulator was built into the alternator, however I'm not sure, How can I find this out and is there a way to test it? Thanks for the replies.

 

I looked on Autozones website and they say that my voltage regulator is mounted on under the hood on the passenger side in front of the shock tower.

 

You may have a poor connection going through the firewall, or a wire with chafed insulation. As you step on the clutch, the pedal reaction force causes the dashboard/firewall to flex and the poor connection is broken or (alternatively) some wire is shorted out.

Do a careful inspection where the wires pass through the firewall on the driver's side of the vehicle, both in the engine compartment and in the cab.

The dashboard wire harness is grounded to the sheetmetal dash support, almost directly below the steering column.

 

I took this truck to a shop and they did a "Load test" (whatever that is) and inspected some of the wiring. They said it is probably an intermitant alternator. However, what I don't understand is why at times it would do this by pushing in on the clutch if is is the alternator. I looked and can't find the wire where the dash harness grounds. Could someone tell me exactly where it is? I also looked at all the wiring where it passes through the firewall and I don't see anything obviouse.