I connected a dvm from the alternator output bolt to the positive battery terminal. It read .6v when one grid relay was powered. .6v x 80a = 48 watts of lost power. Also the large 6 ga wire over on the fender well has a large bullet connector on it that gets warm. That means it’s not doing it’s job perfectly. I took it apart and it was oxidized inside. Sometime I’ll either cut that connector out or try and clean it.

So after the alternator rebuild I went after the grid relays. Before the alternator was removed, I had turned the ignition on but left the engine off. Then I used jumpers to activate the grid relays manually. Each relay was sticking!!! Sometimes both of them would stick in the on position for 10 to 20 seconds at the same time!! Time for a tear down!! The tear down pics will also be in another post. I found the problem in each relay that caused the sticking. Once it was fixed, they would come on for 10 seconds then off. Then on again for 5 seconds. Then off. This was all pcm controlled. I tried to feel each relay to see if they were coming on at the same time. I don’t think they were! I think they were alternating. But the temperature warmed up and they stopped engaging before I could figure it out for sure. So I’ll do that tomorrow morning!!

Here is a Ford type relay mounted between the grid relays and the battery. It looks after market and rigged at that. A couple of it’s wires went to the positive terminal bolt too.

Here are all of the wires stuck onto the positive terminal bolt! The 2 black leads are the fusible links for the 2 grid heaters. The other 2 leads are from the after market looking Ford relay.

Here are the grid relays. One for each of the 2 grid heaters. The main posts were not shorted together as I checked with an ohm meter. Still need to look at more things to see why the current is dropping the alternator voltage down so low.

So now I wanted to see how the field terminal looked on a scope. These pics below are the 2 scope shots I took looking at the upper field terminal while charging. Sure enough there are waveforms present!! It shows the pcm has proper output. I could not get a sync on the waveforms, but at least I got good enough shots to show what a proper pcm output is suppose to look like. The crispness of the waveforms told me the pcm field control was working fine.

Since this alternator has a relay between it and the 12v battery, and the ecm for the truck controlling the ground connection, then a test could be devised that would duplicate either end. For the relay, it could be pulled from it’s socket and a jumper placed across the output terminals. Then I could vary the ecm by just disconnecting it and using some value of resistor to control the current to the field. I’m fairly sure the ecm might be using pwm for controlling how grounded that side of the field gets. It’s works like an electric motor controller. In this testing maybe I will be able to better understand how to devise a stress test for the ecm signal that is controlling the field of the alternator. Maybe a simple resistor to ground with current measurement. Since the field current should be around a few amps worst case, this test holds some merit.

Remove the negative battery cable first!!! You can see several nuts that need to be removed. You will need 6mm, 7, 8mm, 10mm, 3/8″ sockets. Also a 12mm deep socket is needed. It’s very easy to loose these nuts!!!!!

Don’t loose this ground tab when you take the cover off of the alternator!!!

You can see that the top brush is worn more than the lower one. Not sure if this means much. The upper brush is sticking out about .200″. I left the other part attached as it was tough to get to some of the phillips head screws. Their heads are phillips only and soft at that. They don’t have the standard 6mm or 1/4″ hex that so many do. If it gets stripped, it spells trouble. You can see mine is dinged up already from my attempts to get it apart.

Here you can see wear on the 2 slip rings. I’d guess it’s about .030″-.050″ deep. It just means that the brushes have to reach out further to make contact.

The solder joints for the brush leads are here, under the red hard coating. I scrapped it off with a #11 Exacto knife.

I heated up the solder joints and they eventually let the leads pull through due to the spring tension. So there is no need to pull on the carbon part of the brushes. You can see that these brushes look to have a lot of life left in them. Notice that the ones I got from the rebuild shop are radiussed already. One of the springs did not want to come out, so I left it in.

The square ends of the new brushes fit completely inside the springs.

Each brush lead feeds through a passage under the actual brush. That round hole goes straight back to they get soldered.

Just bend the lead and feed the brush and brush lead into place like I did the first one.

Then wrap the lead around the ring lug to hold it in place when soldering. The spring tension will make it hard to hold in place any other way.

Make sure the brushes are sticking out as much as possible without drooping downward at all. Then solder them back in place.

These are about how far new ones will stick out. Mine drooped some as I was installing them onto the alternator. So I’d pull them in another .060″ or so.

Here is the complete kit I got from the rebuild shop, except for the brush holder. It was not included, but this one is in fine shape. I won’t be doing the slip rings or bearings this time around as I’m just trying to debug the intermittent charging problem.

I screwed the terminal post assembly back to the brush holder. That screw needs to be tight and not come loose. Then I added a socket to hold the brushes in place during install back onto the slip rings.

You can see where the screws are reinstalled from the rear of the alternator.

On the passenger inner fender I took apart the big black connector and inspected for corrosion. It was dirty with crud, but not corroded.

Here is it’s mate out of focus. Cruddy but not corroded. Cleaning both of these did nothing to help the intermittent alternator problem. Neither did replacing the brushes.

Update: I had terminals B and C mixed up. So I changed them in the table and also added a pic that shows the green and blue wires going to the alternator.

Working    Not Working
B 14.0v         11.1v
C 6.5-6.8v     1.9v
D 14.5v         12.2v

All I did was wiggle the black connector over on the passenger side inner fender and it started charging again. It is possible however that the brushes are just worn badly. It looks like I might get that ND shield off of the back of the alternator and that would allow easy removal of the brush assembly for inspection/replacement.

Here is a rear view of the alternator. The two studs on the right are the field connections. The one at the very bottom with the plastic shroud around it is the output wire that goes to the battery. The voltage drop from that stud to the battery’s positive post was 1/4 volt. So it’s ok. The ground from the alternator to the negative terminal of the battery was about 1/8 volt.