Removed and surveyed the alternator wiring harness on 1999 LS400

The wires are in good condition but will require harness tape replacement.

The alternator to fuse buss positive cable is tin-plated copper coarse strand 6 gauge wire.

Will replace the 6 gauge positive cable with 4 gauge tin-plated fine strand marine grade cable.

Voltage drop for 12V D.C. circuits is based on round trip Circuit length...so the positive cable measures about 5 feet so 10 feet circuit length.
Voltage Drop = Current x Length x Ohms per foot​​​​​​
This equation allows you to calculate the voltage drop for a circuit of any length and any current flow, if you know the resistance of the wire.


6 gauge wire is shown in brown , 4 gauge in light blue

These graphs assume:

1. 105°C insulation rating: All Ancor wire uses 105°C insulation rating. Lower temperature insulation cannot handle as much current
2. AWG wire sizes, not SAE: All Ancor wire uses AWG wire sizes. SAE wire sizes are 6 to 12 percent smaller, carry proportionally less current, and have greater resistance
3. Wires are not run in engine spaces: Maximum current is 15 percent less in engine spaces, which are assumed to be 20°C hotter than non-engine spaces (50°C vs. 30°C).
4. Conductors are not bundled: If three conductors are bundled, reduce maximum amperage by 30 percent. If 4–6 conductors are bundled, reduce maximum amperage by 40 percent. If 7–24 conductors are bundled, reduce amperage by 50 percent.

Our alternators are rated 100A.

To achieve less than 3% voltage drop at full power (copper wire) requires 4 gauge wire for 10 foot circuit.
This does not take into account 15% thermal derating of current carrying capacity of cable due to underhood heat.

This suggests an opportunity for improvement in the charging system through gauge change.

A few images of the alternator harness:


Close-up.of alternator harness with wire tray removed.

Depiction of wire track removed from harness. This tray runs beneath the engine fastened to engine cradle.

The wire tray easily accommodates the 4 gauge wire with room for the alternator, AC compressor, oil level sensor and steering sensor rack wires.

OEM 6 gauge wire on.left(black.with blue stripe), Anchor Marine 4 gauge cable on left.(correct red color code)

Sensor wires running alongside positive cable in wire tray

 

The OEM 90 degree fuse block terminal lug end was somewhat unique but was able to obtain a solution from Panduit via their supply chain partner Digi-Key. Minor trimming of top tab and elongation of the stud hole will work.

The alternator stud will use Anchor brand Marine rated lug.

The Panduit lug after trimming end. The remaing stud through-hole will be elongated to accomodate fuse box stud.

Side profile of lug.

OEM lug on right. Toyota typical, the lug through hole I.D. is much larger than the stud.

Terminal lugs, insulating tubing and heat shrink tubing.

Panduit part number

Upgraded Alternator harness near completion. Replaced harness tape, plastic connector shells, positive with 4 gauge cable, and wire insulating tubes.

 

I am surprised no one replied to this post. Great upgrade. I cam across this because I will be changing out my starter this weekend and I was looking at replacing the positive battery cable from the starter to the battery terminal .I cannot seem to find anything online regarding a new replacement oem, or how long this cable is. I guess I will wait until I actually have it in hand before I buy a replacement.