GM Alternator 3 Wire or 1 Wire Hookup?


GM Alternator Upgrade – 1 wire or 3 wire hookup?

As street rodders we are always upgrading the electrical systems on our vehicles. And as a result we are always on the lookout for a better mousetrap, so to speak. How that pertains to this question is this. We have all used, or seen, the 1 wire hookup of a GM alternator. Is it the best setup? Maybe not!

The up side of the 1 wire hookup is that, from a wiring standpoint, it is a way cool and simple hookup. Clean and simple.

Is it the best way to hook it up? In my humble opinion, probably not. With a couple of extra wires you get a whole lot more bang for the buck. Here is why.

The up side of a 3 wire hook up has a few very notable facets.

  • It can run a dash light. Warning lights are just that -Warning Lights! That will get your attention way before you have time to check your gauge.
  • You get voltage sensing. What is that you ask? Well it is the capability to sense the REAL voltage at a location away from the alternator. usually a terminal or junction block. So what? Well, wiring being what it is, has some built in losses [length and connections] and what the fuse panel “see’s” is something less than 12 volts if you don’t have voltage sensing. If you have voltage sensing the alternator will step up and put out up to 14 volts to make sure the power is 12 volts at the block, or panel, even with everything on..
  • Price and availability. The same alternators that are being converted to 1 wire use are most of the time 3 wire alternators to begin with! There are some pure 1 wire units but they are mostly marine and commercial diesel applications. And the 3 wire units are in lots of OEM cars and trucks so they are both cheap and readily available both new and used.

Gospel According To Bob ….. So now that you got my version of this issue I say do it with 3 wires. Can you use the 1 wire setup? Sure, if it fits your needs by all means! For a whole lot more on this issue check out these resources.

  1. Mad Electronics “ONE-WIRE Alternators compared to THREE-WIRE Alternators
  2. “Alternator Conversions for Older GM



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