3 wire to 1 wire alternator

[Swampyankee74]

I am converting to a 3 wire alternator to a 1 wire alternator on my 74 gmc c15.  In what way do I do this that my ammeter still functions properly? I have big red wire which goes to the lug on the alternator, and then a big white wire that went to the plug at the alternator, it is also tied to the red wire up by the firewall. Then a smaller probably 14 guage brown wire that went to the plug. Any info would be much appreciated.

[Swampyankee74]

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[VileZambonie]

What alternator did you get? If it is a quality unit they should have provided you with a tech sheet for rewiring it or call their tech line to ensure your factory ammeter will not become a toasty marshmallow. Sometimes the one wire has the factory connections under the plug so you can run the stock setup.

[Swampyankee74]

The alternator is a cvf 140 Amp. As far as quality level I don't know. I have a wiring schematic, but its kinda vague when it comes to ammeter,  just shows running 12 volts to the fuse block. But I'm gonna take your advice and call tech support and make sure I don't end up with a toasty marshmallow. Thank you!

[bd]

The factory ammeter is a shunt type that senses the voltage drop across the 10-gauge red wire connecting the B+ stud of the starter solenoid to the firewall junction block.  The ammeter is protected by two redundant 4-amp inline fuses, one on either side of the ammeter.  As long as you haven't altered the factory wiring between the starter solenoid B+ post and the firewall junction block, AND haven't changed the ammeter connections to the starter solenoid B+ post and firewall junction block, AND haven't eliminated the redundant 4-amp inline fuses, your ammeter is safe and should function as originally designed.  However, converting from the original 36-amp(?) alternator to a 140-amp alternator may dramatically increase needle deflection immediately after initial startup when the alternator charging current output is greatest, because the ammeter is located between the alternator and the battery and is calibrated to the original lower capacity alternator output.

The brown (exciter) wire and white (voltage output sensing) wire can be folded back and hidden inside the harness in case you ever wish/need to revert to the original 3-wire style alternator.

[Swampyankee74]

I have not altered any of that, it is still hooked up stock (in that aspect aspect). I did however put a high tourqe starter in and no resistor wire to the starter. But the wiring you are describing is bone stock. Thank you bd

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[Swampyankee74]

Well you learn something new every day.  I've been staring at this motor for 6 months and sure enough under a rubber cap on top of the alternator is 2 prongs that accept the stock plug. Knowhere in the paperwork does it mention anything about that. Vile you are right again! I'm going to hook it up in the stock manner. Vz and bd thanks for bearing with me. With your help I'm learning my way through this truck.

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[bd]

Did you check with the manufacturer?  Sometimes the two regulator terminals, when hidden by a rubber cap, are bridged and internally connected to power.

[Swampyankee74]

I did not. See, still learning.  I will call them. Thank you!

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[bd]

I should explain, further.  My concern is if the regulator terminals under the rubber cap are bridged, connecting the factory two-wire plug to the regulator can back-feed a reduced voltage to the ignition switch, partially powering any Ignition-2 circuits that share the ignition switch terminal, which would result in a constant low-current parasitic draw on the battery.  So, you should check with the manufacturer of the alternator before calling the installation done.

[Swampyankee74]

Thank you bd. I'm gonna call the manufacturer today. I have a feeling they are gonna say to follow there schematic. And that's what I'll do. I'll post the answer today.

[Swampyankee74]

Spoke to cvf. They strongly recommend wiring the alternator to their schematic.  I guess that is the safest bet.

[Swampyankee74]

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[bd]

The posted image isn't sufficiently clear to read the diagram text.  If you want to maintain the factory ammeter function, the alternator B+ (output) lead needs to connect to the vehicle wiring in the OEM location (i.e., the firewall junction block).  However, the size of the output lead running between the alternator and the OEM location can be increased (e.g., 4 gauge) without impacting the factory ammeter function. 

If you elect to install a high-amperage fuse (rated per the manufacturer's specification or ~120% of the alternator's rated output), it should be inserted into the alternator B+ lead between the alternator and firewall junction block, wherever is most convenient for safe and secure mounting.

[bd]

If you upgrade the alternator B+ output lead to 4 gauge, the 12-gauge red wire "2E" that originally spliced into the factory alternator output lead and runs to the firewall bulkhead connector can be rerouted directly to the firewall junction block but will still need to be protected by a 6" long 16-gauge fusible link.