Hi,

I decided to upgrade my 160 A alternator to the Mechman 250 A (8302250). Reasons I decided to upgrade are because I am running a winch, LED lights, dual 700 w e-fans, and plan to add other electrical accessories. I have a 2009 Tahoe LT with the 5.3L.

I tried asking Mechman questions about what is needed for installing their alternator to handle and utilize the higher output amps. Their response was that everything for the model I selected is plug and play with the addition of running a 0-gauge wire from the alternator directly back to the battery positive post. I asked if I should remove the OEM alternator wire that goes back to the mega fuse, but they said to leave all the OEM wiring alone, and reiterated that all I need to do is just add this 0-gauge wire from their alt to the battery, and leave everything else alone.

To me, this does not make sense to have a unfused wire and the fused OEM (through the mega fuse) one going back to the battery because not only is this redundant, but also this will be bypassing the mega fuse and potentially causing catastrophic risk. But I'll admit that I am lacking knowledge here.

I then mentioned that I am interested in doing the Big 3 and asked if I still need to have the additional 0-gauge from the alt to the batt the way they suggested. They mentioned that it's not 1985 anymore and the truck I have is not a unibody or glued together one, or basically saying Big 3 is not needed without directly saying that. They again said to leave everything alone and reiterated just adding the 0-gauge wire from the alt to the batt positive. Then went on to say that I would do better by spending wire money on their voltage controller (MM-VCI) or one their alternators with RVC bypass. I mentioned that there are many who are doing the Big 3 on these vehicles, so I asked them to explain what they meant. Here is what they said:

"You can choose who you want to believe, its just marketing and ways to sell cable. Been that way for years. The only ground on your whole vehicle is the negative battery post. The alternator makes the power; the battery stores the power. Getting the power to the battery is the first step, then battery to the component(s) that are added to the vehicle. Start adding a bunch useless grounds and you only set yourself up for a ground loop noise situation.

Using the MM-VC1, the “loop” is irrelevant. MM-VC1 over any “wire upgrade” is a no brainer. Volts go up/stay up, amperage draw goes down.

You can buy all the cool internet wiring and connectors you want, it doesn’t change the fact you’re not fixing some crap wiring on a 40 year old vehicle. Those things came with like 40-60 amp alternators. Your truck has/had at least a 140 amp and the wiring has improved over the years.

Quality, not quantity."

My thought at this point after reading and asking questions about this topic for some time is that if I am running a higher output alt than I originally have is to make sure all the main power/charging wiring can handle it. Doing the one larger grade wire and leaving all the other cable oem and attached while seems simple, but it also seems kind of hacky and I thought it odd that they would suggest it. They never gave an explanation as to why to do this way. As for not doing the Big 3, I suppose some of that makes sense, but still, if the OEM wiring is underrated for the alternator output then my bet is the wiring needs to be upgraded to something larger.

My thought now for what for the 250 A alternator install is:
- Run a larger wire (1/0) from the alt back to the connection at the mega fuse; remove the oem wire (probably overkill on the wire size)
- Run a larger wire from the mega fuse back to the battery positive; remove the oem wire
- Run a larger wire from the battery negative through the RVC and to the post on the engine block; remove the oem wire
- Run the smaller oem wire from the battery negative through the RVC to the frame connection that is near the radiator (existing connection)
- Upgrade the 175 A fuse to 275 A or 300 A.

The last point I am not entirely sure of how much risk this may cause to the rest of the system. But if I am running a 250 A alternator, then to me it makes sense that I should be running a fuse that can handle this output. I know the 2015 trucks with a 6.0L OEM 220 A alternator are using at 250 A megafuse, but I am not sure how much different components like the BCM are from my 2009 with a 5.3L and if they are designed to handle more power.

Anyway, do you think my approach is on the right path? Is there anything you would change?
Does MM's suggestions and comments make sense?
What about their comments on the Big 3 and just get their voltage regulator? Almost seems like all this was just some pitch to get me to buy their device.


Anyway, I hope you all can help on this topic.

 

I believe the company representative is correct. The only upgrade needed is alt to battery, although I would include an upgraded megafuse. Downstream from the battery all is the same as circuits all draw the same current. Their current draw does not increase. The increased alt output only charges the battery at a greater rate, hence the increased wire size. Cheers. Wavelength.

 

I finally got someone at MM who gave some explanations.why the extra 0-gauge cable is safe and how it works with your factory wiring.

1. Keep ALL Factory Wiring & the 175 A Megafuse

• Do NOT remove or bypass anything.
• The 175 A megafuse in your underhood fuse block stays exactly where it is.
• This keeps:
  • Factory short-circuit protection
  • ECM current sensing (so your dash gauge stays accurate)

2. The 0-Gauge Cable = Supplemental Path (NOT a Replacement)

You’re adding a second charging path — the new 0-gauge runs in parallel with the factory wire.

Parallel conductors share current inversely proportional to resistance (Kirchhoff’s Law)

How the current splits (real example at full 370 A output):

Path

Gauge

Approx. Length

Current It Carries

Factory Wire

~4 AWG

30–36"

~70–100 A (20–30%)

New 0-Gauge

0 AWG

18–24"

~270–300 A (70–80%)

Bottom line: The factory wire never gets hot — it only sees a small fraction of the total current.

3. Add a 300 A Fuse on the New 0-Gauge

• Install a 300 A ANL fuse within 12" of the battery positive post.
• Why?
  • Protects against shorts or alternator failure
  • Meets safety standards (NEC/ABYC)

4. Grounds

• Your 2009 Tahoe has three solid factory grounds:
  • Battery → frame
  • Engine → frame
  • Body → frame
• These handle over 400 A when clean and tight.
• No upgrade needed unless you have:
  • A winch over 300 A
  • A stereo pulling >500 A
• Just clean and tighten the stock grounds — you’re set.

5. MM-VC1 Controller – Simple & Plug-and-Play

• Gives you manual voltage control (13.8V – 15.0V)
• Takes over from the ECM — no codes, no issues
• No rewiring or ground changes — just plugs into the alternator’s 2-pin connector, switched ignition source and a ground.
• Works perfectly with your stock setup

Quick Summary – What to Do

Step

Action

1

Keep all OEM wires + 175 A megafuse

2

Run 0-gauge from alternator → battery

3

Fuse it with 300 A ANL within 12" of battery

4

Clean/tighten factory grounds



General alternator instructions are hard to write perfectly—every vehicle, engine, idle speed, and country of manufacture is different. Some brands leave just enough overhead for mild upgrades, others don’t. Your Tahoe has solid grounds but an undersized factory charge wire. PCM behavior varies too; this week alone, two 2016 Malibu 2.5L owners—one idling at 650 RPM, the other near 500—reacted differently to the same alternator. One-size-fits-all rarely works. That’s why your 0-gauge supplemental cable (fused at 300 A) is essential—it shares load safely. Matching power and ground gauge never hurts, but your clean stock grounds are plenty.

 

I finally got someone at MM who gave some explantionswhy the extra 0-gauge cable is safe and how it works with your factory wiring.

1. Keep ALL Factory Wiring & the 175 A Megafuse

• Do NOT remove or bypass anything.
• The 175 A megafuse in your underhood fuse block stays exactly where it is.
• This keeps:
  • Factory short-circuit protection
  • ECM current sensing (so your dash gauge stays accurate)

2. The 0-Gauge Cable = Supplemental Path (NOT a Replacement)

You’re adding a second charging path — the new 0-gauge runs in parallel with the factory wire.

Parallel conductors share current inversely proportional to resistance (Kirchhoff’s Law)

How the current splits (real example at full 370 A output):

Path

Gauge

Approx. Length

Current It Carries

Factory Wire

~4 AWG

30–36"

~70–100 A (20–30%)

New 0-Gauge

0 AWG

18–24"

~270–300 A (70–80%)

Bottom line: The factory wire never gets hot — it only sees a small fraction of the total current.

3. Add a 300 A Fuse on the New 0-Gauge

• Install a 300 A ANL fuse within 12" of the battery positive post.
• Why?
  • Protects against shorts or alternator failure
  • Meets safety standards (NEC/ABYC)

4. Grounds

• Your 2009 Tahoe has three solid factory grounds:
  • Battery → frame
  • Engine → frame
  • Body → frame
• These handle over 400 A when clean and tight.
• No upgrade needed unless you have:
  • A winch over 300 A
  • A stereo pulling >500 A
• Just clean and tighten the stock grounds — you’re set.

5. MM-VC1 Controller – Simple & Plug-and-Play

• Gives you manual voltage control (13.8V – 15.0V)
• Takes over from the ECM — no codes, no issues
• No rewiring or ground changes — just plugs into the alternator’s 2-pin connector, switched ignition source and a ground.
• Works perfectly with your stock setup

Quick Summary – What to Do

Step

Action

1

Keep all OEM wires + 175 A megafuse

2

Run 0-gauge from alternator → battery

3

Fuse it with 300 A ANL within 12" of battery

4

Clean/tighten factory grounds



General alternator instructions are hard to write perfectly—every vehicle, engine, idle speed, and country of manufacture is different. Some brands leave just enough overhead for mild upgrades, others don’t. Your Tahoe has solid grounds but an undersized factory charge wire. PCM behavior varies too; this week alone, two 2016 Malibu 2.5L owners—one idling at 650 RPM, the other near 500—reacted differently to the same alternator. One-size-fits-all rarely works. That’s why your 0-gauge supplemental cable (fused at 300 A) is essential—it shares load safely. Matching power and ground gauge never hurts, but your clean stock grounds are plenty.