Another alternator wiring question

[DrDaryl]

My '86 has a stock 12si. The charge wire looks to be 10 ga and goes to a junction on the firewall.  It has a wire spliced to it near the junction that goes to the fuse box.  Another wire from the junction goes to the starter.  2 questions:  what is the purpose of the spliced wire that goes to the fuse box,
and is there a better way to wire this (alt to junction to starter seems like a long distance).  I'm going to upgrade to a higher amp; I will keep the factory 3 wire setup and plan to use 8 ga wire. 

[bd]

The wire 'spliced' to the junction block end of the fuse block feed is a "fusible link."  It is necessary to protect the vehicle from electrical fire.  There are two additional fusible links at the starter.  None of the fusible links are redundant - each 'link' is necessary, since each protects a separate section of the wiring.  Fusible links are used instead of fuses, because links are more tolerant of current surges that may melt a fuse.

You can run the charge lead from the alternator directly to the battery positive terminal through a dedicated and appropriately sized fusible link.  The 'link' is necessary to protect the wiring should the alternator short.  See the tech article, "How to make a Fusible link" by Vile Zambonie.  The size or gauge of the charge lead you use depends on the amperage output of the alternator.  To quote from a different thread:

...If the alternator is rated less than 70 amps output, build the charge lead from 8-ga wire; between 70 and 100 amps output, use 6-ga wire; between 100 and 150 amps output, use 4-ga wire; over 150 amps out, use 2-ga wire.  Protect the charge lead with 6" of the appropriately sized fusible wire at the charge lead's battery connection.  Crimp then solder all terminal ends....

You might optionally consider rerouting the #2 regulator lead directly to the output post of the alternator using a short, unfused jumper and severing its connection with the factory wire that runs to the junction block or starter.  The #2 regulator terminal is the feedback circuit used to regulate alternator output voltage.

The #1 regulator terminal is the 'excite' circuit used to start the alternator charging initially, and is factory connected to ignition through a resistance wire (with gauges) or a charge light (w/o gauges).

[nlauffer]

I haven't really paid attention to where the wires go, but I am getting ready to upgrade to a CS130 and was thinking about upgrading wire size.
If I understand this correct the charge wire goes to junction then starter before going to battery?
If this is true then going from alternator to battery on a CS130 with 4 gauge wire (105 amp) and then to starter, what does the junction block do now and what size should go from starter to junction block? 
I don't mean to jump this topic, I was thinking this might be somewhat your plan.

[DrDaryl]

thanks for the replys.  bd, if I run the charge wire directly to the battery, what would I do with the factory wiring still in place (alternator to junction/fuse block to starter)?  Leave it? 

nlauffer, I did order a cs130 135 amp with an adapter to use my existing 2 spade plug.  Good questions; it looks to me like the positive battery cable goes to the starter,  and the charge wire goes up to the junction and from there to the alternator.  Perhaps bd and others will chime in.  I really don't know much about proper wiring and really want to do this right since I am increasing the amperage quite a bit.

[bd]

I haven't really paid attention to where the wires go, but I am getting ready to upgrade to a CS130 and was thinking about upgrading wire size.
If I understand this correct the charge wire goes to junction then starter before going to battery?
If this is true then going from alternator to battery on a CS130 with 4 gauge wire (105 amp) and then to starter, what does the junction block do now and what size should go from starter to junction block? 
I don't mean to jump this topic, I was thinking this might be somewhat your plan.

The factory routing and connection of the alternator charge lead depends on the year of the vehicle.  Consult the appropriate year wiring diagram to determine the wiring configuration for your particular vehicle.  Charge lead routing in the square bodies was somewhat circuitous and could run to the junction block or all the way to the starter.

The post regarding wire size is a guideline.  For 105 amps out, you could use either 6- or 4-gauge copper cable.  The more current you chronically demand from the alternator the greater the wire size needed.  So, if you plan to load your alternator heavily, for example greater than 70 amps on a continuous basis, choose 4-gauge cable.

To wire a CS alternator (a definite upgrade from the factory SI), follow the link posted in Alternators.

[bd]

thanks for the replys.  bd, if I run the charge wire directly to the battery, what would I do with the factory wiring still in place (alternator to junction/fuse block to starter)?  Leave it? 

nlauffer, I did order a cs130 135 amp with an adapter to use my existing 2 spade plug.  Good questions; it looks to me like the positive battery cable goes to the starter,  and the charge wire goes up to the junction and from there to the alternator.  Perhaps bd and others will chime in.  I really don't know much about proper wiring and really want to do this right since I am increasing the amperage quite a bit.

DrDaryl, since you're converting to a CS alternator, ignore my post on the regulator wiring modifications - those mods pertain only to the SI series alternator.  Wiring for the CS is covered in the link referenced in my last post.

The cleanest install includes removal of the 'abandoned' charging system wires from the factory harness.  Just be sure any wiring you remove isn't part of a feed circuit for something else, since the cab and chassis both source their electrical power via wires that connect to the starter and the firewall junction block.  If you decide to leave the abandoned wire in place, terminate the bare end.

[DrDaryl]

Thanks for the help.

[DrDaryl]

Well, one more question!  Read the post on how to make a fusible link and will definitely make sure I don't leave off any  the factory had in place, but if I chose to purchase a factory style fusible link, how many amps would be appropriate using a 135 amp alternator?  Thanks

[DrDaryl]

Please disregard my last post, will make a fusible link as described by Vile in technical pages.  Thanks