4-wire alt help (not for the weak!)

I have an 87 LX carbie with the 3-wire alternator, 65A output
I have a 96 4-wire alternator to install, however I need advice on how to wire the regulator without an ECU. My testing indicates that the setup on the 96 is exactly the same as the 88-89 LXi alt.

According to http://www.acuravigorclub.com/Timely...imely1201.htm:
alternator "C" terminal is an output signal from the ECU (Engine Control Unit) to the alternator. This is the "charging control" signal that turns the alternator on and off through the internal voltage regulator. I GUESS THIS IS SOMETHING I NEED SO THAT IT DOESN'T RUN AT 100% ALL THE TIME

the alternator "IG" terminal in the illustration, is also power, this one from the ignition switch through a fuse (No. 2) in the Under-Dash Fuse Box, to the alternator. This powers up the voltage regulator whenever the ignition switch is ON. NO PROBLEM HERE

the alternator "L" terminal has only one job in life, and we all hope he never has to do it. He controls the warning lamp on the dashboard. NO PROBLEM HERE

the alternator "FR" terminal is the "charging rate" signal from the alternator. It's [a signal] to the ECU...

The FR signal (WHT/RED) communicates to the ECU how "hard" the alternator is working to meet the electrical demands of the car, including the battery and any loads which aren’t monitored by the ELD.

This signal is a square wave that varies in pulse width according to the load on the alternator. The ECU puts a 5V (approximately) reference voltage on the wire. The voltage regulator will drop this signal to approximately 1.2V in proportion to the alternator load... UMMMM :dunno:

The voltage regulator puts approximately 8.5V (reference voltage) on the control wire, labeled "C" (WHT/GRN). When the ECU drops this signal to ground, the alternator will stop charging. If this wire is shorted to ground, the alternator will never charge.



Alright, so based on what I've read, I need to hook up IG, and L, and a circuit on the other two wires if I wish to control it... but:

1) If I leave the last two disconnected shouldn't it charge on maximum?
2) Besides intalling an ECU just to control my alt, how can I build a circuit to control it?




PS The alts have the same mounting points and rotation, however the 96 alt has 90 amps output and a 5-groove pulley. I'll attempt the swap once I know how to make the new one charge without an ECU :cool:

The 4th wire is just a signal wire for the ECU so that when there is a lot of load on the alternator it bumps the idle up. If you leave it disconnected, the alternator will still function as it should without any problems.

You should be able to leave the C and FR connections unconnected and have it work. Generally cars are designed to be as failure proof as possible. So if by chance one or both of those connections were to fail you would NOT want the alternator to just stop working. You would want the ECU to throw a code but still have the alternator keep charging the battery; so you can get the vehicle in for service without killing the battery in a couple hours.

C|

well it didn't line up as well as I thought but I rigged it on there and it charges even with only the blk/yel ignition wire hooked up. No more massive voltage drops when I bass, even with the a/c and lights on. Now I have to make a new bracket for the top bolt and wire the charge lamp.
Pics coming soon

pics....i remember some one did this mod but for the fuel injected cars its more of a bolt on.