Alternator Swap Out - Converting A 240-Z's."external regulator type" to the 78+ 280-Z's "internal regulator type" alternator.

Contributed By: Steve Golik, IZCC #356

The Purpose of this page is to give the reader an understanding of how your present externally regulated alternator, can be replace with a newer model, internally regulated alternator

Converting to an internal regulator alternator

Question: I would like to know if anyone has converted from the external
regulated alternator to an internal. What wiring did you change?

Answer: First a little background: The 60 amp internal regulator alternator was used on the '78 280Z and then the non-turbo 280ZX. I have also seen it on the '78-'85 810/Maxima and the '81-'85 720 pickup trucks. It is marked "LR160" on the case. There was also a 70 amp version (marked LR170) that was used on the 280ZX turbo's.

[Note: It looks like the '84-'86 non-turbo 300ZX 70 amp alternator could be used as well, but the wiring connectors are different, so get (i.e., cut it off) the corresponding engine harness connectors as well if you get one of these alternators. I'll write this up this conversion later.]

Because I don't like to give instructions without some explanation of what you are doing (it makes troubleshooting easier), I will start by describing the internally regulated alternator's electrical connections:

1. An "L" connection which goes to a "switched" 12V supply. By this I mean a 12V source that is active only when the ignition switch is in the ON position. I use the mnemonic "L" for "lamp", the alternator warning lamp (if used) is in series with this connection. This terminal also supplies the "excitation" current to the alternator field winding at engine turn on, allowing the alternator to begin producing voltage as the engine is ramping up to idle speed. Once the alternator rotor is turning fast enough, it generates it's own supply for the field winding and the current in the "L" connection stops flowing. The warning lamp (if used) goes out.

2. An "S" connection which goes as close to the positive terminal of the battery as physically possible. The "S" connection "senses" the battery voltage and this is the voltage that the regulator is tying to control. This connection has a high impedance, so it only draws only micro amps from the battery, so it can be left connected without fear of battery discharging.

The "L" and "S" connections are in the plug connector on the rear

of the alternator that looks like the capital letter "T". The top

of the "T" is the "S", and the other part of the "T" is the "L". Or

in crude ASCII art:



                    :   -------   :

                    :....  |  ....:

                        :  |  :

                        :  |  : "L"


3. An "A" terminal, which is the output of the alternator, which also is connected to the positive terminal of the battery. This connector carries the charging current. Because of the high currents this wire must carry, it is a low gauge wire, which means it has a large cross sectional area. For safety reasons, a fusible link should be in series with this connector. The "A" terminal is the insulated threaded stud on the rear of the alternator.

Of course, someone may ask: "Why do you need two separate (the "S" and the "A") connections between the battery and alternator?". It is because of the fact that even large wires have some resistance, and therefore there will be a voltage drop between the alternator and the battery when the battery is being charged. If the regulator sensed the alternator output (which is higher in voltage) and not the battery terminal, the result would be undercharging of the battery. Now there are alternators which work this way, but they need a fairly large diameter charging wire to reduce the voltage drop. The separate "S" connection is a much better method of regulation.

4. There is a "P" terminal on the 280ZX turbo alternator (but have also seen it on a few of the non-turbo 280ZX alternators). There is not a corresponding connector on the engine harness to mate with the "P" terminal, even on the turbo 280ZX's. So, the "P" terminal is not used/needed.

5. Finally, there is a ground connection on the alternator, although the case is a pretty good ground connection to the engine block.

Now, the following procedure only applies to the 240Z. The 260Z has electrical connections between the regulator and the interlock module and the electric fuel pump, so it's more difficult to convert to an internally regulated alternator, but I have a procedure for it as well. Please email me directly if anyone is interested. I have not looked into converting a 280Z, but I would think that it would be possible as well.

1. Disconnect the battery.

2. Unplug the external regulator and note the color code of the wires that are on the regulator connector of the engine wiring harness. You will be connecting some of these wires together, so get another plug from a junked regulator or cut the one off your old regulator. Now the wire colors I will be referring to are on the regulator connector of the engine wiring harness. This is because although the regulator wire colors match the engine harness with the stock regulator, I've noticed that some aftermarket regulators have a different wire color code.

3. Connect the white wire to the yellow wire. This connects the battery to the "S" input.

4. Connect the black with a white stripe wire to the white with black stripe wire. This connects the "L" terminal to a switched 12V.

5. Disconnect and unbolt your old alternator. Bolt up the new alternator. Depending on what particular internally regulated alternator you use (I've seen different pulley sizes), you might need a different length belt.

6. At the alternator, connect the white with red stripe wire of the engine wiring harness to the threaded stud (the "A" terminal) on the alternator. This connection provides the charging current for the battery. Connect the black ground wire to the alternator. Don't forget to include any bypass, or filter capacitor. Plug the two-pin "T" connector into the alternator.

7. Re-connect the battery and start the engine. With a good digital voltmeter measure the voltage directly across the battery terminals. This is the charging voltage. It should be 14.7V +/- 0.3V, but this voltage is a function of the ambient temperature and the state of charge of the battery. If the voltage reading is not correct, then re-check your wiring. More than 15.0V indicates that the "S" connection may not be connected correctly.


I had this problem and thought I'd share the solution. Many thanks to Ken Osman and Steve Golik who provided the solution:

When an internally regulated alternator is put into an early Z and the external regulator is removed, you often have the problem that the car will not shut off when the key is turned off.

You have to put a diode in series on the wire that goes to the "L" terminal on the back of the alternator. The "L" terminal is the bottom contact on the "T" shaped connector.

You have to connect the cathode of the diode (identified by a stripe on that end of the diode) to the "L" terminal and the anode (other end of the diode) to the wire that previously went to the "L" terminal. In my case (71 240Z) this was a white with black stripe wire. This prevents the "L" terminal current from feeding back into the ignition circuit when the key is turned off.

The diode I used was a 1N5402, other people have used a 1N5400 or a 1N5062. Easy fix to a vexing problem.

Side note: when I fixed this I connected the Yellow wire in the harness which leads to the alt to the "S" terminal (top of the "T" connector) on the alt - PO had spliced white/black wire into both the "L" and "S" terminals - my under hood light started working. WHOOOHOOOO!

71 L28 now shuts off with the key!

Original Article: 7/798 Last update: 7 March 03 -cjb