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Author Topic: Factory engine wiring questions  (Read 140 times)

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Patches

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Factory engine wiring questions
« on: February 23, 2019, 04:42:16 PM »

I have a 1990 C34 1.25.  I am putting my engine back together after making many of the suggested upgrades. Full disclosure:  I have a poor understanding--but getting better-- of all things electrical in my boat.

When hooking up the new harness, I note that I have two "4 AWG" positives coming off the "C" post of the battery selector switch and running to my engine compartment.

One of the 4 awg wires looks to be bundled with the two positive cables running from the selector switch (1 and 2) to the two batteries in the battery compartment.  It runs from the selector switch down under the macerator pump, takes a hard turn aft through conduit into the compartment under the head sink, and then goes around to the back side of the engine before ultimately attaching to the starter post. A negative follows the same path, and was bolted to the bell housing.

The second 4 awg wire runs from the "C" post down by the macerator and then out into the central bilge area.  From there it joins a negative wire in some clear tubing/housing and pops up in the floor of the engine compartment-roughly under the alternator.  This positive wire is also connected to the starter, but the negative was originally connected to the "-" on the starter--not the bell housing.

As some of you know, I am staying with a small 51 amp alternator, internally regulated, for a while before doing a larger battery bank upgrade in a few years.  I'm trying to figure out why I have two 4awg positives, and two 4awg negatives coming into the engine via different routes.  It would seem that a single 4awg positive and a single 4awg negative would handle it--No?

My new internally regulated alternator, with the AO and remote sense wires will run to the solenoid post, and should charge the batteries back through one of the 4awg positives to the "C" post on the selector switch, correct?

Or do I need to keep both of those 4 gauge positive wires connected to the starter?

If not, was the intent that one of the 4awg positives (the one running under the floor/bilge area) could/would be used for the AO to go directly to the batteries if the owner later upgraded?

If so, can I use that positive for that purpose when I upgrade my battery bank in a couple of years, and also upgrade to an externally regulated alternator?  Or is the 4awg too small for that purpose, and I should really be going to a 2awg for the AO when I upgrade later?

Thank you in advance!  I appreciate any enlightenment you can provide.

Patches
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mark_53

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Re: Factory engine wiring questions
« Reply #1 on: February 23, 2019, 05:35:09 PM »

Patches:
The OEM wiring leaves a lot to be desired.  If you haven't had starting problems yet consider yourself lucky.  Check out the Critical Upgrades for discussion on why.
http://c34.org/bbs/index.php/topic,5078.45.html

I've rewired in a dedicated starting battery using 4AWG wire and it has worked fine for 4 seasons. No doubt larger wire will provide less voltage drop but is more expensive and harder to work with. I kept the cable runs from the start battery to the engine a much shorter 4ft vs the 25ft OEM route.  I've also kept my OEM 51amp alternator.  Maybe someday I'll upgrade it but haven't needed to yet.  I think I would add solar before a larger output alternator.  I used mainsail's basic wiring diagram located here.
http://c34.org/bbs/index.php/topic,8790.msg62933.html#msg62933

Then I created my own schematic for my particular installation located here.
http://c34.org/bbs/index.php/topic,8790.msg63977.html#msg63977
A previous owner may have made changes to your boat so it would be best for you to make a diagram of your existing wiring and become familiar with what you have then a new diagram of what you want.

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Stu Jackson

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Re: Factory engine wiring questions
« Reply #2 on: February 23, 2019, 05:41:00 PM »

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
If so, can I use that positive for that purpose when I upgrade my battery bank in a couple of years, and also upgrade to an externally regulated alternator?  Or is the 4awg too small for that purpose, and I should really be going to a 2awg for the AO when I upgrade later?
>>>>>>>>>>>>>>>>>>>>>>>

Patches,

I don't know about the earlier part of your post, but for this ^^^ question, the answer is that a 4 awg will be too small for use with a larger AO.  My 100A alternator upgrade required #2 wire based on 3% voltage drop (actually larger than required but they don't make #3 wire!!! :D).  I ran a new #2 from the AO to the house bank (properly fused at the battery end).  I left the OEM #4 NEGATIVE and paralleled it with a new second #4.

Happy detective work.
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KWKloeber

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Re: Factory engine wiring questions
« Reply #3 on: February 23, 2019, 09:28:19 PM »

patches

who knows what a PO did, but my guess would be that s/he ran another #4 to combat the too high V loss in the single #4.  maybe s/he had a source for cheap or free #4.  why is ran a different route, who knows?

The battery negative(s) should be on the starter bolt, not the bell housing.

The regulator sense wire should ideally be run to a battery post, not to the solenoid.  That way the regulator will adjust AO to compensate for V loss between the solenoid and the battery.

-k
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