2G to 3G alternator upgrade walkthru 4.9L 1988

[ShadetreeSeattle]

Alrighty, today we will be doing the 2nd gen to 3rd gen alternator switcheroo on a 1988 Bronco1 with the 4.9L 300CI inline 6.
the install for the 4.9L was not that difficult at all, the factory alternator bracket already had mounting provisions for the larger alternator. I have to break up this post into parts because of the 10K character limit on here.

Part 1: Parts/tools needed: (parts all sourced from o'reilly auto)

1x 125A circuit breaker (on shelf in electrical isle)
2x 24" 4AWG wires with crimp end ring terminals on each end
1x 15A blade fuse holder
1x 15A fuse
1x small pack of 3/16 female quick disconnect terminals or a donor 3G alternator wire harness
1x small pack blue crimp butt splice terminals
1x small pack assorted yellow crimp ring terminals
1x m8 x1.25 by 30MM bolt
1x small pack of washers, 3/16 ID or whatever you have laying around.
Zip ties
Electrical tape (get the nice scotch stuff, it's actually somewhat tolerant of under hood temperatures)
Socket set, imperial and metric
A decent crimp tool, one which has the non-insulated tooth. (the ones which just squish the terminal flat are useless)

Okay, PART 2. 2G removal and prep for 3G.
Here's the final install BTW, what I ended up with.


Here's the old, Existing setup with the 2G alternator below:


Step1, disconnect battery, remove the old alternator, remove belt. I was a daredevil and left my battery connected because the truck runs like #%$@ for a while if the computer looses it's keep-alive memory. I don't recommend keeping the battery connected. I was being stubborn. Don't be dumb like me. XD



One beer in! one bolt out! haha. Notice in below photo how I have removed the air pump previously, if your air pump system is defunct/non functioning anyways, perhaps a good time to pull it out and re-route the belts since you will, with this 3G alternator upgrade need to install a custom length belt anyways. Always consider if you have emissions laws which will not allow your vehicle to pass without an air injection pump and also, all the other things one needs to do to remove the entire air injection (smog pump) system.


Another pic of my belt routing without air pump or a/c


Here's the original 2G alternator, with the 2 and 6 o'clock mounting ears. on the engine's alternator mounting bracket we will no longer utilize either of the mounting positions used by the 2G alternator.


Alternator removed, observe below, the original 2 and 6 o'clock mounting holes (more to the right) and the 12 and 6 o'clock mounting positions to the left we will now be utilizing. Ignore the top most threaded hole on the mounting bracket and the very bottom most swivel mount which was originally for the air pump. neither will be utilized.


Below, observe the original mounting ear configuration between the old 2G alternator and the new 3G alternator. We will not be using either of the original mounting holes from the 2G alternator as they are spaced narrower from eachother and in a different position from our 3G alternator.


Below, observe the backsides of the 2G (upper in picture) and 3G (lower in picture) alternators. With lower mounting ear to the right we see that the electrical connections are facing the wrong direction from the original, 2G alternator. To fix this we remove the 3 bolts from the 3G's casing and carefully rotate the rear half of the alternator case CCW to the next position it can bolt back together. This will aim the voltage regulator and V+ connectors downward and toward the passenger side instead of in toward the engine block which will not work.


Again observe how the 3G alternator's connections will face toward the engine block instead of away and down.


Bolts out, gently pry the casing enough to unseat it so it can be rotated. the casing is in three pieces, the front half is bottom in below image, mid section is middle in image, top section is the top (rear) of the alternator. the front (lower in image) and mid are to be separated slightly and rotated CCW to the next point which the bolt holes line up. do not try to rotate the top (rear) and mid sections as they are electrically connected together.

 

[ShadetreeSeattle]

Part 2: installing the new 3G alternator and main V+ wire/circuit breaker:

Alternator clocked in the correct direction and the three case bolts secured now, we can bolt it on!


The top bolt from the original alternator is not the right size, the new alternator has a metric M8 by 1.25 thread pitch.


Below are the bolts and washers I got to solve the issue with the original top bolt being too big for the new alternator. I never ended up using the washers tho.


For the bottom bolt, it's the right size BUT! the alternator has a burr at the front half of the case casting which is not allowing the bolt to pass thru. likely only an issue with the one I picked up, lazy engineering. =/


I naturally chose to hone it out with a large flat blade screwdriver. Took me 3 min.


The lower bolt fits now. yay. Part of me thinks that the lower hole is designed with the ever-so-slightly smaller tolerances of a metric bolt, thus why the imperial bolt was a tight fit, why I needed to debur the edge of the hole. Whatever. let's mount it in the truck!


Install the lower bolt first, it's fussy, a tight fit and it helps to be able to rock around the alternator to get the bolt to thread in properly. once the bottom bolt is threaded in, go after the top bolt before snugging both down to torque. I never look up the torque specs, i'm sure they exist. i gave it one ooga jugga for the smaller top bolt and two for the bottom.


Top and bottom bolt in and snugged down, below we see that the original belt will not reach. I guestimated about 4" more belt was needed. I took the old one to the oreillys and asked the friendly parts helper assistant person to find me some belts with a higher number range than the original I had. I took three different lengths with me, found the one which fit on but kept the tensioner under enough load and took the others back. if you get one too long, the tensioner will not load down the belt enough and it will squeal and break. too tight and well, you won't get it on.


my original belt was a 6K790 I ended up with a 6K827 fitting pretty well. the alternator needed no shimming to line up with the belt path. the picture makes it look a little misaligned but it's not. lines up just like the last one.


Next is the electrical. I ended up getting a longer 4AWG wire, initially i got a 12" but got a 24" after the fact. Below are the 3/16" female quick disconnect terminals, the butt splices, the circuit breaker and i already had the one yellow ring terminal i needed in a separate kit. I also got some smaller washers to help ensure the most metal-to-metal contact between the 4AWG wire's eye terminals and the smaller bolt connections i was making between the alternator and circuit breakers. Not pictured is the 15A fuse holder and fuse i will get to in a bit.


Below, I used a washer between the nut and 4AWG wire on the V+ connection at alternator to ensure good contact with the oversize ring terminal crimped onto the wire and the alternator. also used washers on the connections to the 125A circuit breaker.


Connections made between alternator V+ (Big red connection) and circuit breaker's load side. The line and load side does not actually matter, the circuit breaker trips regardless of current flowing one direction or the other. not very sure why it's even labeled as such, it's not an intelligent device, just a spring loaded switch which opens when a thermal limit (a certain ampacity) is exceeded.


Other side of the main V+ circuit, after the circuit breaker. I was going to connect to the input side of the starter solenoid, as how the previous alternator V+ wire was installed, but i opted against it as the terminal was already stacked with a lot of other ring terminals. I got a longer 4AWG wire and ran directly to the battery terminal. Two beers in now. not bad.


Here's what i ended up with, connecting the V+ wire from the alternator straight to the battery, via the circuit breaker. Now with the main charge wire connected we need to work on the rest of the electrical to the alternator.

 

[ShadetreeSeattle]

Part 3, Voltage regulator wiring and cable management:

Here i'm holding up the original wire harness from the 2G alternator. all the tape and split loom tubing needs to be removed from the wire harness, but leave the white-ish fiberglass heat shield wrap that's closer to the 3pin connector, we will reuse. Once the tape and loom is removed we will be re-using a portion of the wiring, discarding the two BLK/ORN wires and original fusible link which have now been replaced with our chunky 4AWG wire and circuit breaker which we already completed. Not pictured but I already disconnected the GRN/RED wire from the body harness for ease of removing the old tape and split loom. the single wire connector is located beneath the starter solenoid by the fender apron. it's a squeezy type connector, not difficult to separate. top of picture is it disconnected.


Once all the tape and split loom is removed, we need to cut the YEL/WHT wire from the fusible link splice where it meets the two BLK/ORN wires. the two BLK/ORN wires and the fusible link get discarded. The purpose of the YEL/WHT wire is to supply a 12V source to the voltage regulator for the FIELD circuit, more about this later.


With all the tape and split loom tubing gone and the two ORN/BLK wires discarded here's the remaining wire harness necessary for the voltage regulator operations of the 3rd Gen alternator. Pictured below is the 3 pin connector which goes to the voltage regulator with wires YEL/WHT, GRN/RED and WHT/BLK.
A quick overview of these wires functions: (We will go thru them individually as we proceed thru the project)
#1, YEL/WHT was snipped away from the splice which adjoined the two discarded BLK/ORN wires and the YEL/WHT to the fusible link. this fusible link was connected to the battery's + terminal via the starter solenoid. the YEL/WHT wire needs to be connected to the battery's + terminal to get 12V all the time. When the GRN/RED wire gets 12V from the ignition switch ON circuit, it enables V+ to pass from the YEL/WHT, thru the regulator when the regulator deems charging demand is needed.
#2, GRN/RED is connected to the ignition switch's IGN output thru the dashboard cluster. it's wired in series with a resistor and the alternator dummy lamp. when the key is in IGN position, 12v flows from the switch, thru the resistor and dummy light and out from there into the engine compartment to the passenger side fender apron to the single wire connector underneath the starter solenoid. This wire tells the alternator to turn on and begin regulating 12v between the YEL/WHT and WHT/BLK wires depending on demand.
#3, WHT/BLK will be looped back into the alternator. (more in a bit) There's a small, single wire terminal adjacent to the 3pin terminal on the alternator. The WHT/BLK wire provides 12V to the field circuit of the alternator (the single wire terminal beside the 3 wire terminal. when the alternator is receiving 12v from GRN/RED it passes thru 12V from YEL/WHT to WHT/BLK depending on loading that the voltage regulator deems necessary.

ANYWAYS! let's get to wiring.


Let's prep the WHT/BLK wire. it will take one of those 3/16 quick disconnect crimp terminals. Note how i strip twice the ammt off and fold it over, highly recommend doing this. the wire will never slip out of the terminal once crimped



Crimp it! Crimp it good! (i use the toothy part of the crimp tool even though it says for non-insulated connections.) it punches a hole into the plastic but makes for a very firm connection, unlike squishing it flat.



The WHT/BLK wire will get doubled back toward the 3pin connector it came from. it will eventually plug back into the alternator, to the single pin connector immediately beside the 3pin connector on the alternator.


Thermal wrap slipped back over the top of the wires from the 3pin terminal, the WHT/BLK wire protrudes with a little extra length to reach the single pin terminal next to the 3 pin terminal.


Plug the WHT/BLK wire into the single pin terminal on the alternator, the one right besides the 3pin connector. (in hindsight, this was a huge PITA to plug in after mounting the alternator because the connector was facing down and i couldn't see the pin inside the connector. If I had harvested a wire harness from a ford with the 3G alternator and spliced the appropriate single pin connector onto the wire instead of using this crimp quick disconnect terminal, this would have been much easier while mounted. if using the 3/16 crimp terminal I recommend installing it before bolting on the alternator. the connector should fit firmly, if not, double check you actually seated it onto the pin. if it disconnects, no charge will be produced.



Go ahead and plug in the 3 pin connector to the alternator's voltage regulator. Beneath you will see the single wire WHT/BLK 'field' terminal plugged in and beneath that the V+ charge output from the alternator all hooked up.


with all our connections at the alternator done, let's move to the two remaining wires. Let's start with the YEL/WHT wire. we will need our fuse holder and 15A fuse seen below.


you can likely cut back some of the YEL/WHT wire, or double it back inside the loom toward the alternator if ya want to keep some extra just in case. Our YEL/WHT wire will need to get connected to one end of our 15A fuse holder as seen below. the other end of the 15A fuse holder will get a yellow ring terminal applied. The yellow ring terminal will be bolted onto the 'load' side of circuit breaker, the wire going from circuit breaker to alternator. also, see below i have began taping up the wire to the alternator and re-installed a portion of the split loom tubing.


Better image of the above:


Taped up and split loom tubing added, the yellow ring terminal from the YEL/WHT wire via the 15A fuse is now attached to the 'load' side of the 120A circuit breaker. the only wire continuing onward in the split loom tubing i am holding below is the GRN/RED wire which will run off to the fender apron and plug back into the single wire connector beneath the starter solenoid that we unplugged earlier.

Zip tied down and the GRN/RED wire plugged back in beneath the starter solenoid we are ready to test it out. re-connect the battery that you were smart enough to disconnect in the first place, pull out a multi-meter, you should see a nice 14.5V ish charging voltage, which after warmed up and running for a while should taper down to 13.5v. if with engine running you only see battery standby voltage, (less than 13V) or an overvoltage condition (14.99V or greater) than something is wrong and will require troubleshooting. Cheers ya all!