86 Ford truck eloectric issue.. On the right track??

Hey guys,

I have a 86 Ford F-250 with a diesel engine (which really don't play into the equation..)

I've had it roughly 5 years, and have put about 30k on it since..

I haven't drove it very much since late spring (500 miles or less), as the transmission was starting to act up badly. I finally scraped enough together and had the trans rebuilt, and just wrapped up the project the other evening.

I drove it tonight (after dark) for the first time since probably late March.. I noticed that my lights wanted to "pulsate". The faster I drove, the more noticeable it was. When I got home, I put a volt test to it.. Shows 13-14 at idle (swinging scale on load tester, hard to get a exact reading), and will creep up to right around 16, then drop back close to 14. Rev the truck up, does the same, just faster. It was not doing this when I last drove it at night (to the best of my recollection at least)

The batteries were new in February, the alternator is about 2 years old.

Am I pretty safe to assume the voltage regulator is going out? (external type, mounted on right hand inner fender well)

Sorry for the long post, thanks for the input.

Brad

Bad diode in alternator or maybe a brush tying to stick or bounce?

Put the elec. system under a full load. Lights, wipers, a/c or heater, etc. If it shows a discharge you likely have a bad diode in the alt. If not, could be the voltage reg. or as suggested a stickin or bouncing brush. Good luck. Keep us posted, you got our curiosity going now.

check to see if the engine is grounded good to body and to battery ground.
may just take a jumper cable from battery ground to the altenator frame. only a guess
oldart

possible a couple of things could be, maybe volt reg, also check grounding straps fron engine to body, where ever they are put at, ground from batt to motor, to frame, to body panels, maybe alt is losing a diold at different speeds under load of acc.

You know! oldart may have a point, about the ground, being as the tranny was recently worked on! A ground may have been left off, during the tranny repair?

I'll make sure to check the body ground tomorrow.. However, IIRC, it is grounded to the back of the head in this case.. I can't recall unhooking anything when I dropped the tranny. BOTH batteries are grounded directly to the engine block, and no trouble starting, so I am thinking they're ok.. However, when I get the money I'm gonna treat the old girl to all new battery cables, just for good measure (some of the insulation is getting kinda bad.. I'm sure they're all original cables)

I know I have a ground strap running from a battery to one of the inner fenders, as I had a ground issue (I thought) once before, but I found a hidden wire had a bare spot where it runs to the top of the headache rack, and I never removed the "extra" ground.

It was pretty close to full load (shy the blower motor running) when I did the voltage check this evening..

I didn't take the consideration of a sticky brush when I was thinking of it earlier.. Is there a "simple" way to rule that out?

Brad

follow the big wire off the alternator,you will probably find a green spot,possibly at a fuse link or solder connection

No simple way to check the brushes that I know of. The brush assembly is easy to remove and not too expensive to replace. If a brush is bouncing, it could be due to an uneven spot on the armature. or, just a long shot, since it has not been driven for awhile, wonder if a mason or "dirt dauber" built a nest in it?

The only thing I have to add is if you do replace the regulator make sure and run a ground wire from the battery to the regulator with one of it's mounting bolts.When a ford regulator starts overcharging many times its due to it not being grounded good enough, it blows the regulator almost instantly if thats the problem, and will blow the new one too. jstpa

Check the ground from the back of the engine to the body. Sometimes when the engine is tilted back a little like when installing a tranny that ground strap can break.

Rick

Like others have said, make sure all connections are good and remove the battery cables and make sure they are not corroded. Clean the battery posts. Put your voltmeter on the field wire going to the alternator and see if it fluctuates too. If it is still fluctuating you can eliminate the voltage regulator with a 7 ohm high wattage resistor hooked to the battery and to the field terminal. If it now shows a steady charge, your voltage regulator is bad. Auto Zone will check your alternator for free from what I hear. I don't know if they check voltage regulators or not.

A grounding problem or some other bad connection is quite possible. Take a good voltmeter and check the voltage from the negative battery terminal to different ground points: alternator case, regulator chassis, body. Any difference over a hundred millivolts is a serious problem. You can do the same thing with the positive cable to the alternator output and regulator sense lead.

If I recall correctly, Ford alternators regulate by grounding the field, so a bad connection between the regulator and vehicle ground might explain your symptoms.

Yep, you hit 'er right square on the head.

Assuming you've already made sure that the belt is tight, you've got a voltage regulator gettin' tired.

Allan