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I had a Mechman 8206250 alternator installed last Monday. I spent some time on a dyno Tuesday morning. The car sat since Tuesday evening and the battery voltage was in the red when I attempted to start the car for lunch today; it was slow but eventually started. I did not have this battery problem before the shop performed the alternator replacement. Testing at the battery terminals on Monday, the alternator was charging at 14.9-15.0V. During the time on the dyno and the drive home, HPTuners was reporting the Control Module Voltage to generally be in the range of 13.7-14.1V.
The Mechman alternator requires a blue wire to be connected to a switched ignition source. The shop installed an add-a-tap fuse splitter to the fuel pump fuse slot under the hood and connected the blue wire to that splitter. We also cut off the old ring terminal at the alternator end of my upgraded battery cables (link below) and replaced with the terminal provided by Mechman. Mechman says GM didn't introduce computer controlled alternators until 2005, conflicting with information that a local alternator repair shop told me in the past. Mechman also said I should investigate why there is a nearly 1V discrepancy between the noted charging voltage at the battery vs what is reported by the scan tool.
Fuel pump triggers for a few seconds then turns off with just key on
Then stays on with engine running.
That makes it a bit of a funky place to use, but likely fine.
I would suspect the t tap more than anything else. I've had a ton of trouble with those things not piercing the wiring well enough, and even when they do they don't hold a very good connection.
I would cut the wire and use a weather proof butt connector, they crimp and heat shrink down. i use those a ton in automotive wiring and love them because when they shrink they also emit a sealing goo that seals the connection.
Solder and heat shrink works, but you need the sealer to keep the connection from seeing moisture.
I wouldn't be too worried about the voltage discrepancy just yet. I see that some times on bone stock cars here at the shop. But do keep an eye on the voltage, make sure it doesn't go above 15
I'm not exactly following your suggested changes; here's a photo of how it's currently connected to the fuel pump socket. I temporarily pulled some of the blue wire out of the loom to show it. The black in the middle of the red wire is simply a sleeve to act as a grommet when it passes through a small U-shaped opening created in the edge of the fuse box. If there's a better solution than connecting it to the fuel pump socket, I'm open to all suggestions.
And the provided docs are below. I do not have a fuse anywhere in my charging system as suggested; I have the complete OEM sound system. Harness adapter Docs pg1 Docs pg2 Docs pg3 Docs pg4
Last edited by JimMueller; Dec 3, 2020 at 11:00 PM.
From post #4 in the above thread:
"I got the answer. The harness is correct. The exciter wire connects on the car side to turn on the alternator AND to turn off the battery light. It has to be connected to an ignition voltage source (12VDC when the key is turned on)."
I printed out that post, as well as provided all the documentation above to the shop, but I don't think they spent much time thinking about the correct wiring.
From post #4 in the above thread:
"I got the answer. The harness is correct. The exciter wire connects on the car side to turn on the alternator AND to turn off the battery light. It has to be connected to an ignition voltage source (12VDC when the key is turned on)."
I printed out that post, as well as provided all the documentation above to the shop, but I don't think they spent much time thinking about the correct wiring.
Teach me to try and answer a question before I finished my coffee, lol. Totally missed that there was 2 sides on that plug.
Battery was dead this afternoon, down to 5.7V, after sitting about 48 hours since I last drove it. But the last time I drove it was only for about 10 minutes. After jumping the battery, battery quickly registered 14.9V on the top battery terminals. Definitely seems like a parasitic draw was acquired with the new alternator install.
Took the car back to the shop, and the tech spoke with Anthony at Mechman. Anthony said to check the yellow wire coming off the alternator to see if it was hot with key off. It was hot, so Mechman is going to email me an RGA. Looks like I need to pay for shipping one way, and labor to replace the alternator twice more. Until I get this alternator removed I'm going to be pulling the tap connection in the fuse box before the car sits for long periods of time.
Not a great experience so far given the cost; I hope this isn't representative of their long term reliability.
Does your power antenna for the radio still work? I had a similar issue, but mine was the blue wire coming loose due to a bad crimp. The power antenna quit working immediately after that.
FYI, Mechman Tech Support told me to tap the blue wire into the power wire for one of the front injectors. That seems to work perfectly.
Does your power antenna for the radio still work? I had a similar issue, but mine was the blue wire coming loose due to a bad crimp. The power antenna quit working immediately after that.
FYI, Mechman Tech Support told me to tap the blue wire into the power wire for one of the front injectors. That seems to work perfectly.
I do not have a power antenna. I haven't removed it yet. One thing I thought about in their directions was they dictated using their eyelet on for their larger stud. So now I have a larger eyelet than what is on my old alternator stud, a mismatch that Mechman said was undesirable. Unsure what I may experience with that mismatch until I get it back on the correct size stud.
I took it to another shop and they moved the switched power wire from the fuel pump fuse to the PCM fuse. No problems since I picked it up about 10 days ago.
I took it to another shop and they moved the switched power wire from the fuel pump fuse to the PCM fuse. No problems since I picked it up about 10 days ago.
I would have used one of the pre-existing Accessory fuses on the fuse block, trigger the feed to the alternator getting the actual power from the primary hot feed fro the main power buss.. If you look at most car wiring diagrams, the alternator circuits are typically fairly isolated. YMMV.. Good luck.
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Mechman alternator with switched ignition source 
