Hi all, I just picked up a 1971 F100, it is strictly a work truck, so, not pretty, but runs ok.

Anyway, I have been checking out these boards the last couple days, and there is a lot of great info in here.

I am hoping you can help me with a problem I am having with my F100.

When I got the truck, it wouldn't crank, so I bought a new battery. Got it to crank, and start, but at times, it would crank really slow or need to be jumped, so I assumed the alternator wasn't charging, and picked up a rebuilt alternator, and new voltage regulator.

Now, the problem(s), not sure if they are related... It still cranks slow sometimes, but eventually the cranking speeds backup, and the old girl fires up.

The bigger problem is a voltage fluctuation. I first noticed it driving at night, depending on engine speed, the headlights would switch rapidly from bright to dim. It wasn't a random switch, so I am pretty sure it isn't a loose wire. So, a couple days later, I put my voltmeter on the battery, which read 18.5 volts, while the engine was idling. Then, I revved the engine a while, and the lights started doing their flicker thing. While they were doing that, I read the volts at the battery, and it fluctuated with the flickering between 16 volts, and 18.5 volts. The flickering happens so quick, it may not give the meter enough time to register exactly how low the voltage is dropping. Another note, whenever the truck is running, the battery gauge in the dash is constantly pegged at "C".

To top it all off, when I shut of the engine after this test, the battery was boiling.

Anyone got any clues on what I can check to see what is wrong? Sorry for the long post.

Thanks alot!!

Ryan

 

You have a serious overcharging problem, the meter should never show more than 14.5vdc give or take a few .1vdc
The regulator is probably defective, most parts places will check it free, but since it is new I would return it for another one.
Another thought would be you are getting full voltage to the alternator field causing it to over charge which could be a wiring problem.
Any how do not run the truck like this, it will if it already hasnt "screw" the battery. Batteries do not like to be boiled.

Sparky

ps
Try another regulator and let us know how it works.
The slow cranking could be corroded battery cables.

 

I agree with Sparky about the charging system; 18+ volts is way too high. As for the engine turning over slow, another thing to check is your starter. If it has worn bushings or a "going bad" armature, it can give the symptoms you describe.

OldFords Bad attitudes

 

[updated:LAST EDITED ON 23-Oct-02 AT 09:52 PM (EST)]Well, I put in a new regulator, and took the current "new" alternator to schucks to have it tested. It only read 9 volts on their tester.. weird.. anyway, he found one that read 12 volts, and he sent me away with it in hand.

So, tonight, I put in the new regulator, and new alternator. Started up the truck, and got a reading of 14.5 volts on the battery... yay I thought! But, it started fluctuating between 14.5, and 15.5, so I went into the cab, and with the engine running, saw the battery guage bouncing like crazy between D and C. The interior light was flickering too. So, something was still wrong. I put the old "new" regulator back in (different brand), and bammo, same 18V to the battery with guage pegged at C. 5 mins of engine running with the old "new" regulator, and it started with the light flashing again.

I am thinking the two different regulators are handling whatever problem I have differently, thus the two different reactions... one sending 18 volts, and one sending between 14.5 and 15.5 wildly.

I think it is safe to rule out a bad regulator, and bad alternator at this point. But, I won't swear by it

Could it be the battery for some strange reason? It is new also.

Any more ideas?

Thanks for the help guys, electrical problems can be such a pain to figure out!

 

Check all the regulator and alternator connections to make sure they are solid. Be sure all the ground connections are good. Let us know what you find.

 

One step further... Get a piece of emery cloth or fine sandpaper. Remove each of the heavy 10 gauge (8 gauge?) wires between the battery and the starter. Sand each connector clean and then put them back on. Do this on the battery terminals and ground (negative) line also. I have a strong hunch your starting problem will go away.

The 18 volts is another problem that needs to be rectified.

 

>Check all the regulator and alternator connections to make
>sure they are solid. Be sure all the ground connections are
>good. Let us know what you find.


I took the screws the mount the regulator to the chassis, and polished them up.... Got all the grime off em, so they can make good connection. All the wires attaching to the alternator and regulator are old, but solidly hooked up. Unfortunately, that didn't help any

A couple questions:

I have been told that once the truck is running, I should be able to disconnect the battery, and if the alternator is good, the truck will continue to run. Well, I tried this with the old alternator, and with the new one, and the truck died each time. I tried removing both the ground, and the hot wire off the battery. Would this indicate some sort of problem?

Does anyone know where I can get a wiring diagram for this old girl, as I am seeing my only other option here is to trace every wire, and see if there is some sort of short involved.

For those of you who know electrical, what could cause an alternator that puts 12V on a test machine at the auto parts store to put out 18V once installed in my truck? That doesn't make sense to me.

Thanks again for any advice you all can offer, I am dreading having to trace every connection in this thing to find the problem.

 

It is not the best practice to disconnect the battery. It acts like a big filter for the alternator output. The voltage output of the alternator depends on current going thru the field terminal of the alternator. Check with your voltmeter at the field terminal. There is a voltage adjustment on the regulator. The regulator with the low cover is a solid state version. You can replace the older electro-mechanical type with the solid state version.

 

Of the two voltage regulators I have, one is tall, the other is short. The tall one cost twice what the short one cost.

With the tall one hooked up, I get a fairly consistent 18 Volts to the battery, with the short one hooked up, and I get the erratic 14.5 - 15.5 volts.

Are you saying there is a way to adjust the tall one to force an output of 14.5 volts?

If so, that would fix my problem I think.

 

The "tall" vlotage regulator is the old mechanical/electro kind
it has relays and coils and vibrating points etc etc in it. I dont think they are adjustable.
The "short" one is the newer electronic style it has diodes and transistors and other neat stuff in it. Some of them are adjustable by a little screw in about the centre of the circuit board. Usually they are factory set and work fine and when they break it is easier to put in a new one that try and fix the old one.
To me it still sounds like a voltage regulation problem. The regulator sends varying voltages to the alternator field terminal to increase or decrease the alternator output voltage to keep it roughly between 13.5 & 14.5 vdc under varying loads.
The regulator that causes an 18 vdc output is most likely bad, it appears to be putting full field voltage all the time to the alternator.
The one that is running at 14.5 to 15.5 could be good how accurate is your voltmeter? It should not be fluctuating though. It could be a bad cell in the battery do you have another good battery you can try? Also could be a load switching off and on like maybe a loose wire, or a bad connection.
It is better to have the 14.5 fluctuating regulator installed vice the 18 volt one. The over charging is not not good for the battery or the life of all the light bulbs.
There could be a good possibility that battery was damaged by the 18vdc overcharging and boiling that happened. Now the other voltage regulator is being screwed up by the bad battery.

Sparky

 

I was having problems with starting when I first got my truck a few years ago. Not only did my connections need cleaning, the battery cables were so old that they were practically falling apart. I ended up replacing all of the heavy starter and battery cables. I did what I could with the alternator cables. Replacing the starter and battery cables made a world of difference... my starting problems went away! I am beginning to wonder if some of my other electrical problems (Guages not working, etc) are related to brittle old wiring... it might be something worthwhile for you to check out.

James Kern
1970 F250 4x4

 

Sparky may have a hit with the battery being damaged. It wouldn't hurt to try another one. The battery voltage should not be changing erraticly. The older style regulator can be adjusted by bending the spring arm on the voltage limiter relay. To decrease voltage, bend the arm upward. The arm is what the coil spring for the relay is connected to. The arm is at the bottom end of the coil spring.

 

ok, here is the latest update. I pulled the battery out of my other truck, which is working just fine, and still have the exact same problem.

I have swapped out the older style regulator, and am running the solid state one, that has the rapidly switching voltage, but doesn't go over 15.5V.

Now, on to what I have discovered...

I installed a tach, and needed to plug into two of the fuse banks. one for the key switched power, and the other for the dash lights. I tested, and found which fuse bank was which, and plugged in. When I turned on the headlights, my tach lit right up. So, I shut off the lights, started the truck, and the tach registered the RPM just fine. Then, I turned on the lights, and the tach immediately died. So, out came the voltmeter again, and started testing at the fuse bank. Here is what I discovered:

With the truck off(but key on)/lights off, I have 12.5V to all of the fuses, except the dash lights fuse. The dash lights fuse registers 0V. Just like I would expect it all to be.

When I turn on the headlights, with the truck off, I get 12V to the dash lights fuse. That seems right to me.

With the truck on(key on of course)/lights off, I have 8-10V to all of the fuses, except the dash lights fuse. The dash lights fuse registers -6V (that's negative 6). NOT like I would expect it all to be!

When I turn on the headlights, with the truck running, I get about 7V to the dash lights fuse, and the rest of the fuses remain unchanged.

So, anyone have any ideas in the light of this new discovery?

Thanks!

 

Anyone have any ideas on this one?

 

Reblanc: I believe you have a bad ground somewhere. The way the tach acted seems to confirm it. This is a common problem on older vehicles, especially those in the rust belt.
Check these grounds:
Engine to electrical: I use a negative battery cable with an added wire. The primary ground is the engine block itself, and the other secondary wire goes to the fender well.
Engine to body: There should be a grounding strap on the backside of the engine mounted to the firewall. Any wire will do here.
Frame to body: I have a grounding strap between the firewall and the frame itself.
Check all your under-dash grounds and connections out, and clean up the ones you have, and see if that works.
Good luck!