b_stone81

So I have a 2001 4runner sport with 138000 miles and at night when I hit the breaks or roll down a window my headlights dim a lot. Anyone know why or how to fix?

SoCal4Running

Could be undersized or corroded Alternator charge wire. The positive wire that goes to the battery is a little small IMO.

The alternators are not very high output so getting the energy to the main harness efficiently is important.


My old 86 4runners headlights would even dim with the turn signals and I could watch the volt meter deflect every time they flashed.
Simply switching to LED brake and turn bulbs solved that but using the rear window still dimmed the lights and deflected the meter.

After changing alternator wire to 6 Gauage instead of the stock 8-10 gauge now the meter holds steady no matter what I do. Lights on, heater on and use rear window and it still won't tick.

SoCal4Running

Double post... Stupid iPhone

b_stone81

Okay thanks. I'll do that. You think a alternator with a higher output will solve it as well?

RAD4Runner

Alternator with higher output may help but that would only be a band-aid fix if you have high resistance in your wires (because they're too thin and too long) and connectors because of corrosion.So start by cleaning your connections, and upgrading alt-batt wire like SoCal Running suggests.

Also check you schematic and actual wiring:

• Are power wires thin?
• Does ground wiring run from bulb to cabin to dimmer light and back to engine compartment?
• Does high bulb current run through dimmer switch?
• Do you have excessive voltage drop caused by your wiring?
  With lights on, and everything else off:
  Measure battery voltage directly at posts.
  Measure voltage across bulb filament.
  What percentage of battery voltage do you measure across bulbs? The Higher the better.
  Compare to my "after" % readings on my Headlight Retrofit post

Retrofit post explains these flaws and my fix for them. These flaws are not unique to Toyotas/4Runner. Also google Daniel Stern Lighting, where same flaws are discussed.

wyoming9

iTrader: (1)

I have found lots of things poor grounds degraded battery cables terminals etc.

which all help to cause this problem .

another major one is not having a big enough battery with enough capacity to handle the demand .

Now i always upgrade all my electrical systems and run the biggest capacity battery

SoCal4Running

Grounds are hugely important in an electrical system.
Not just the connection to the frame but also the wire to the connector.

My truck being older had more time on the wires and such but I found corrosion "green" on my Batt wire 24" away from any splice or connector, just there by itself.
All the connectors needed replaced though especially the ones at the alternator because of the heat cycles from the exhaust.


Not sure if on your 01 if it is a know issue with dimming lights. If it is I suggest new thicker wire, new copper lugs at both ends of wire with a proper crimp and solder.

I did change my alternator to a mid 90's Supra alternator going from 55A stock to 65A.
This isn't a huge improvement but with the new wire it shurly makes a difference.

Like said above the higher output alternator will not really help I the wire is in poor condition.

This is all speculation of course without looking at your setup as it is.

wyoming9

iTrader: (1)

As an example I have the stock alternator with upgraded cables and best battery that will fit.

I have no problem winching with a Warn :jessica::jessica::jessica: 9.5 TI in a 1987 4 Runner