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by Angel Morales

Bosch voltage regulators are famous for being "lazy" when it comes to output voltage. They are just not good at recharging the battery and keeping voltage at the right level in warm weather and low battery conditions. This article ilustrates the procedure to replace the internal Bosch regulator with an external Motorcraft electronic regulator or equivalent. The benefits are: more efficient battery charging, better voltage output and stability, and according to some, about 15% higher alternator amp. output.

OK, here is the complete HOW-TO!:

Brush holder modifications

  1. Disconnect the battery.
  2. Remove the regulator/brush holder assembly from the back of the alternator. This is a good time for replacing the brushes if they are worn out. You might as well get a used regulator and modify it while your car is working with it's stock setup.
  3. How you have to disable the built-in regulator. You don't need to remove the old regulator from the brush holder, just disconnecting it will do. This is done by isolating the brushes from the regulator. Use a small file to cut the metal connections to the regulator. Remove the little thingy that looks like a transistor (I am not an electronics genious). IMPORTANT: the 3 leads MUST be TOTALLY cut from the stock regulator.

    Shown are the leads that MUST be cut to disable the stock regulator
  4. Ground one of the brushes to the brush holder body. Use a piece of 18 gauge wire (about 1" long) soldered to the base of the brush and to the brush holder base. (Diagram coming soon to help!)
  5. Now solder a 16 gauge wire to the other brush base. This wire goes to the external regulator so it has to be long (3.5 feet long to place the regulator next to the RPM relay in my 242 Turbo).

    Fig 1. Bottom view of the modified Bosch regulator / brush holder
  6. Install the modified regulator/brush holder assembly back on the alternator. IMPORTANT: Bend the metallic piece that makes contact with regulator inside the alternator to isolate it from the regulator (if you don't, the battery light will stay on). All you have different looking at it from the outside is the long wire coming out from the alternator (use a fiberglass wire protector sleeve like the ones used on H1 bulbs for all the wiring, gauge 12 for sigle wires, gauge 4 for the four wires going to the regulator).


AHA!!! This is the neat part!

FIG 2. This is the back of the alternator and its connections.

FIG 3. This is the regulator and it's terminals.

REGULATOR MODEL: Ford Motorcraft electronic voltage regulator part #GR-540-B (See "European Car" Jan '97, page 128). I am testing a cheap replacement for the Motorcraft regulator that's said to work just as good. If it doesn't, then I'll buy the real thing. It's a RENARD P/N 1093.

I: Connect the battery light wire from the car's wiring to this terminal (originally connected to the back of the alternator). You'll need an extension from the original wire.

A: Connect this terminal to constant positive (+) from the battery. Use a long (3.5' for the 240 Turbos) 16 gauge wire from the alternator output pole. (see FIG 2, "Battery (+)")

S: Connect this terminal to battery light terminal on the back of the alternator (see FIG 2., "Light")

F: Connect the long wire that you soldered to one of the brushes to this terminal.

Make sure to crimp and solder all terminals instead of just crimping them. Use hi-temp epoxy to cover the alternator light connection instead of electric tape (In my car, the alternator is under the turbo).

Fig 4. Here is my alternator ready for installation.

As I said before, I will place the regulator next to the RPM relay in my 242 Turbo. Just make sure the body of the regulator gets good ground and presto!

The guy who did the modification on my alternator told me that Bosch alternators usually get lazy with batteries that are low, especially in our climate (70-90 F year round).

COST: I spent $20 including a generic regulator, wire sleeves (very nice touch) and terminals (if you choose to buy the higher quality Motorcraft regulator, the total cost might be about $15 higher). I need your help. Please send me your comments and corrections if something is not clear enough.

Neither the author or TurboBricks take resposability for the results from this modification. If in doubt, please consult your auto electrician.


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