Hi, all. Having problems with search this morning so I'm posting the question directly.

I'm helping my friend with his 1984 Bronco XLT - 4.9L I6/4 speed manual. The alternator had a bearing failure and since I happened to have a spare 3G alternator of the appropriate type to convert his truck we're doing that later on today. I'm pretty sure I have most of the process in hand except this - I know I will need to bypass, disable or disconnect the stock ammeter that his truck came with in order to safely install the 3G. How is this best done? I can't seem to find anything in the archives about it at current. Thanks in advance.

 

You just need to disconnect it.
I believe the wire colors are red/orange and yellow/green.
They both pass through the four pin connector and attach to the charge cable.

Pic from the old RJM website.

 

Ok I got to ask a stupid question?
Why does the amp meter need to be disconnected/by passed?


I know the 3g alt will put out more juice but the truck is still going to pull the same amount of power it did before the change no?


Dave ----

 

Because the *shunt* wire is not sized for the increased output of the 3G alternator.
And the 3G will put out more at idle than the 1G will put out at redline.

Say you had trouble with a cold start and the regulator called for the alternator to keep putting out more amperage in order to bring the battery up to the 14.35V set point, the shunt would not pass enough current.
The undersized ammeter wiring (which is in parallel) then becomes a filament and the insulation catches fire or the ammeter itself has a meltdown.

 

Here is a link with photos of the Red / Yellow wires.

https://www.ford-trucks.com/forums/1...l#post14726314

When you add a larger power wire, to handle the higher amp output of the 3G ALT, the new heavy gauge wire goes to the battery and thus bypasses the shunt. Don't try to use the current power wire unless you install a 60 amp fusible link.

Jim

 

Interesting............

 

Most of those 1G's on gas engines were 35-45A units.
Even the 65A 2G units didn't have large enough wire to handle their own output.

I've got the 2/0 cable and Busmann Megafuse holder kit that RJM used to sell.
Overkill for sure since a single V-belt can only transmit so much power.

 

I agree with Jim; No need to mess with the ammeter wiring at all, it's part of the old alternator charge wire which is too small to use with the 3g. So just tape the old wire up in the harness and forget it.

 

At work I am working on a '82 F150 that we are putting a 2012 5.0L Coyote engine in. On this alternator I did not by pass the factory wiring. What I did was cut all regulator wires from the truck and kept the one main hot wire on the relay for the starter that powered the truck. I cut the end off the alternator charge wire and taped it up an ran a 10ga wire from the alternator to one side of a 100A mega fuse I mounted in place of the starter relay. I then ran two 10ga wires from the other end of the mega fuse to the positive battery cable as "charge" wires. The main factory wire to supply power to the whole truck was then attached to the other side of the mega fuse along with the charge wires to the battery cable. In this configuration the ammeter is still connected but bypassed as current can flow around it without being forced to flow through the ammeter. The ammeter still works some what, you turn the headlights on with key on engine off it does drop a hair but when the engine runs the ammeter really doesn't move.






Now on my personal truck since I planned on running auxiliary lighting that will tax the circuitry on the truck, I will be running atleast a 8ga charge wire from the 3G alternator to my starter solenoid with the factory charge wire hooked to the alternator as well. I wont be cutting any wiring just bypassing the main charge wire by running a secondary wire for charge. Then I will branch off the power for auxiliary lighting off the fuse side of the mega fuse and move my headlight relay hot side to the mega fuse side as well this way it will free up space on the solenoid.


thing is though just running a single wire from the alternator output to your solenoid will effectively remove the shunt as current has alternative paths to take than all through the ammeter.

 

In your first example the amp meter only works in the Discharge direction as this wiring is still intact. To test this and prove it to yourself draw down the battery with the head lights before starting the engine. If it worked right the needle would swing to the Charge side then come back to center. The Amp Meter should only move, needle left or right, if current is flowing into or out of the Battery.

On your personal truck the amp meter will not work in either direction due to the added 8ga charge wire. Most of the current will flow through the new larger wire.

Also if the mega fuse failed it would / could force way to many amps through the original truck wiring. As stated in post #7 ... anything more than 40 amps is very risky as the stock wiring is to small. The added auxiliary lighting would be supplied but the 3G ALT and of course other loads like the heater fan, radio, Ignition....

The head light would be on the battery side of the failed mega fuse and thus you would still be able to see where you are going.


Jim

 

Which is why the OEM power wire is on the battery side of the mega fuse. The only wire before the megafuse is the actual charge wire that I made from 10ga bulk wire. If the alternator tries to put out more than 100A it will pop the fuse but the truck would still have power through the battery though.


The amp gauge which I did not see as I did not start the truck up, the owner of the shop did that but he claims the needle did swing slightly to the charge side.


This is why I jumper off for high load systems. On the customers truck the power wire for the PCM and cooling fans and even the power for the radio and amp is coming from the mega fuse on the battery side. That way the OEM wiring has to power nothing other than the factory systems which should keep them from failing. I am even doing a headlight relay conversion on this truck like I did on my personal truck especially considering this is a 140A alternator. I don't want that kind of current possibly going through the factory switch.


For my personal use, I planned on keeping the OEM wires intact in the off chance I ever decide to go back to a 1G alternator. Doubtful but I always try to keep my vintage vehicles in a state to be put back original without replacing major components.

 

I guess I messed up which wires where on which side of the mega fuse, on my truck I used a 100 amp circuit breaker, it has never tripped the breaker. I have a single V belt on the ALT.

I also left my original 2G ALT wiring intact as I carry the old one as a spare behind my seat.

On a side note to those that add headlight relays or other loads to the battery directly... If your ALT / amp meter wiring is still stock, the amp meter will read on the charge side when you turn on your headlight.
This is because the system "thinks" you are sending the amps to charge the battery.

So it really doesn't take much to mess up the amp meter indication. I just used the amp meter needle swing to the charge side to verify the headlights are working OK...

Jim

 

Thanks guys, that answered my question - I disconnected and capped the ammeter wires at the 4 way connector. My install will not be using any existing charging wire as I routinely use megafuses, large gauge cable, etc., when dealing with any alternator upgrades. Thanks again!

 

Not sure if you ever heard of "rocket man's classic cougar innovations". At rccinnovations.com, but he takes ammeter's from our trucks and converts them over to read volts. $40.00 plus your core, or $75.00 with out core. That way you could still have a gauge that worked.

 

My Cougar buddy (Joe) introduced me to the voltmeter conversion.
Gary and Jim both have good writeups in their 3G swap threads.

I even think it's in the stickies.

### This was the answer to your first thread, eight years ago. ##$