Late model alternator wiring question

[Jimal]

Work continues on my serpentine belt conversion/intake manifold replacement.



And I'm at the point where I need to work on the alternator wiring. Last year I converted from an externally regulated alternator to an internally regulated unit using this wiring, but connecting a jumper from the charging terminal to the "1" terminal.



Now I'm converting from that to a late model alternator. I have the pigtail, and I have these instructions I found from the GM Performance Parts kit:



The instructions reference using either the Generator light or a 50 ohm resistor inline to the "L" terminal on the alternator. How does this translate when you have a gauge, which wire from the first conversion should I be connecting to the "L" terminal, and what wires can I eliminate?

[chevy_mike]

I did mine like the top pic but I had to put a 5 watt diode from the blue to brown wire. With the HEI, it would keep powering it when I switched off the key as it would back feed to the HEI. I also do not recommend jumpering the charge wire to the 1 post. This does not allow the alt to sense any vehicle load on the battery (like turning your headlights on) and it won't ramp up the power to compensate for any loads. It really should go to the horn relay, which is where the fuse block and battery should attach to. I can't recall if we put a resister to replace the original charge bulb or if the diode was enough.

[Jimal]

Originally Posted by chevy_mike

I did mine like the top pic but I had to put a 5 watt diode from the blue to brown wire. With the HEI, it would keep powering it when I switched off the key as it would back feed to the HEI. I also do not recommend jumpering the charge wire to the 1 post. This does not allow the alt to sense any vehicle load on the battery (like turning your headlights on) and it won't ramp up the power to compensate for any loads. It really should go to the horn relay, which is where the fuse block and battery should attach to. I can't recall if we put a resister to replace the original charge bulb or if the diode was enough.

But if the wire going from the BAT+ terminal on the alternator also goes to the horn relay like the #1 wire, you're effectively creating the same circuit as I did with the jumper, just with more wire.

[gmachinz]

I suggest using either the horn relay as a common junction or a separate junction altogether. Then, use a 100-150 ohm resistor inline (if you have stock gauges, aftermarket gauges won't need it) and solder it inline on the remote voltage sensing wire between the alt Plug and the gauge.

[chevy_mike]

Originally Posted by Jimal

But if the wire going from the BAT+ terminal on the alternator also goes to the horn relay like the #1 wire, you're effectively creating the same circuit as I did with the jumper, just with more wire.

I know what you are saying but it take into account any voltage/current drop for the whole system. I know it's cleaner to just use the jumper but you can be limiting your system. If going through the effort to change, why not do it the best way. GM still does this. If it wasn't something they really needed, they could save the extra cost in wiring by eliminating it.

My best friend who has been doing auto electrical work for 25+ years, showed me this. He used to do it your way but always had issues with dimmer lights or pulsating lights from big stereos or the flasher. Going to a positive reference point hookup (i.e. like the factory horn relay), this eliminated all of these issues.

Here is a great 3 page article on why and what happens in real life.

http://www.madelectrical.com/electri...esensing.shtml

[VetteVet]

All you need to do is extend the brown wire that went to the external voltage regulator to the "L" terminal and wire a 75 ohm to 300 ohm resistor inline with the brown wire and the "L" terminal. The resistor should be between 1 watt and 5 watts.

Then run a red 12 gauge wire from the "S" terminal to the main power junction with the large wire from the alternator output terminal. If you use a 94 or later CS style alternator then you won't need the red sensing wire. Don't use a jumper between the S terminal and the large output terminal for the reasons stated.

It's this simple and notice that the battery gauge wires are connected just like the original truck wires.



This is the diagram for the SI alternators showing how to wire them up. You only need a 10 ohm resistor which you already have in the bulb of the light cluster or a 10 ohm resistance wire on the ignition switch on the ACC terminal.

When you convert to the CS alternator you only need to upgrade the resistor and the brown wire will go to the "L" terminal and the red sensing wire will go to the "S" terminal. I don't have that diagram on this computer but I may be able to post it later from my other one.

We also recommend upgrading the alternator output wire to a 10 or 8 gauge wire for increased current carrying capacity.

This thread should show the CS wiring along with a whole bunch of good information on the conversions.


http://67-72chevytrucks.com/vboard/s...d.php?t=417872

[Jimal]

Thanks for the info everyone. I need to redo that harness since my truck originally had the alternator on the passenger side. At the end of the day adding the extra wire and the resistor isn't that big of a deal. I just hope my local Radio Shack is still open...

VetteVet, I'd love to see that other diagram. Looking at your diagram, the bat wire and the sensing wire still end up at a common point.

[VetteVet]

Originally Posted by Jimal

Thanks for the info everyone. I need to redo that harness since my truck originally had the alternator on the passenger side. At the end of the day adding the extra wire and the resistor isn't that big of a deal. I just hope my local Radio Shack is still open...

VetteVet, I'd love to see that other diagram. Looking at your diagram, the bat wire and the sensing wire still end up at a common point.

It's in post 26 in the thread I linked in my post above.

The batt wire and the sensing wire do end up in the same place.