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My P-gaskets needs replacing so while its all apart I was going to replace my old 65A alternator with a 100A alternator I purchased some time ago. I've been told to upgrade the thickest wire leading to the alternator to at least a 8 Gauge. I'm not that familiar with the engine harness layout and I know very little about wiring in general so before I head over to West Marine for cable I thought I'd post up here first.

My brown (thickest cable on alternator) goes counter clockwise around engine (on top) connects with a whole bunch of various things before it connects to the starter. Does this sound correct? Looks like I would need about 5 feet of wire. Because this wire lays on top of the engine it has a heat shield wrap. If I can't reuse the existing one what would you use? I have a bunch of fiberglass mesh hose meant for this stuff but I thought I'd get some heat shield tape on it first What brand of heat shield tape do you recommend?

Is there any other wire I should upgrade while I'm in there? How about the wire from the starter to the battery? Also, Ancor (my preferred choice) doesn't have brown cable, only black, red, green, red, white and yellow. If I wanted the correct color what would it be?
 

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The main power wire goes from the alternator to the starter solenoid where the main lead from the battery connects. I would use 4 gauge welding wire.
 

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Yes Carl, the brown wire is the one that you are upgrading. I did it on my truck, so you are welcome to come check it out. I took apart the old harness, and remade it with the larger wire. I would also be happy to help you do it if you would like a hand.
 

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Discussion Starter #6
I will likely take you up on that, Toby. what heat shield products did you use? Did you also upgrade the starter to battery wire?
 

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Discussion Starter #8
What did you use for heat shield?

The main power wire goes from the alternator to the starter solenoid where the main lead from the battery connects. I would use 4 gauge welding wire.
 

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IIRC brown is the correct color. But someone should check a manual if you want to be sure.
Red is universal for hot wire though!

I would think 6 gauge should be more than enough.
opinions vary but I'm a big fan of crimp and solder.
 

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What did you use for heat shield?
For the wire? It should not need a heat shield as it is nowhere near the exhaust. The insulation of the cable should be rated for engine temperature.
 

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To be clear there is no need to modify/hack into anything on the main harness. Simply add a heavy gauge wire as John is suggesting from the charge post on the alternator back to the positive post on the starter.
 

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Discussion Starter #12
I'm confused. I thought the idea was to replace the brown wire, not add an additional wire?

Is there exposed circuitry on the engine block? While trying to measure the brown wire I almost welded my tape measure to my engine block. Yes, I should always disconnect the battery. Need to get my OJOP connectors on there so it's not such a hassle.

To be clear there is no need to modify/hack into anything on the main harness. Simply add a heavy gauge wire as John is suggesting from the charge post on the alternator back to the positive post on the starter.
 

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Adding another wire would be the same as going to one thicker wire. Depends on what you are going for, some people like the cleaner look of one.

The brown wire or the red wire from the starter to battery are hot. They are literally connected to the battery positive so if you bridge from alternator post or starter post to the block you're completing the path to ground.
 

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I'm confused. I thought the idea was to replace the brown wire, not add an additional wire?

Is there exposed circuitry on the engine block? While trying to measure the brown wire I almost welded my tape measure to my engine block. Yes, I should always disconnect the battery. Need to get my OJOP connectors on there so it's not such a hassle.
DC current travels on the surface of the conductor which is why dc wire is nearly always stranded instead of solid like AC. The more surface ie gauge, the higher the amperage capacity. By taking a single large gauge conductor from the alternator to the starter you have fixed the high amperage needs ie-most direct path to the battery. You can certainly cut into your existing harness and make the same upgrade, just pointing out that isn't necessary, as said it becomes a matter of personal preference. My opinion is that leaving the existing and adding a direct large gauge is more than simply upgrading the existing, and more is better.
 

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I just did this on my 200TDi. Except I removed the brown wire completely as it was poorly spliced at one point and ran clockwise around the entire engine (maybe 4 feet or more of wire). I then added a new, shorter wire that went direct from my 120A alternator to the starter solenoid.
 

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Discussion Starter #16
Got it, thanks! Rovers North did the harness install. It looks legit so I think I'll leave it be and add a much shorter, addition wire as suggested. While I'm at it should I get a thicker gauge between battery and starter as well? Not sure what is on there currently.
DC current travels on the surface of the conductor which is why dc wire is nearly always stranded instead of solid like AC. The more surface ie gauge, the higher the amperage capacity. By taking a single large gauge conductor from the alternator to the starter you have fixed the high amperage needs ie-most direct path to the battery. You can certainly cut into your existing harness and make the same upgrade, just pointing out that isn't necessary, as said it becomes a matter of personal preference. My opinion is that leaving the existing and adding a direct large gauge is more than simply upgrading the existing, and more is better.
 

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Not sure what is on there currently.
You should not need that. It is sized for the starter current, which is hundreds of Amps.
 

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Carl, since you're out here on the coast, you can get everything you need at West Marine. Go for their Ancor marine grade stuff and get the proper marine grade terminals as well. You will need to crimp the terminals with a proper crimper; depending on the gauge, you can use a small hand crimper or one of the bigger ones that looks like bolt cutters. For 4 AWG, it's probably going to be the big ones. I bought my Odyssey battery at Battery Systems and they let me borrow theirs. Someone locally might have one. West Marine might have one to lend, as well. Brian did not, last I checked.
 

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Discussion Starter #19
Can someone tell me what's going on here?
 

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