What will cause the 120amp fuse to blow in ls400

well 99% of posters here, (same squawk)
did all that wrong. (endless posts same acts wrong)

2 ways wrong./ (never scanned the PCM first)
and did not check all fuses next)

The service job done wrong is next)
and last worse yet, did not do step one in all service manuals
on Alternator page, failed to disconnect the nEG lug of the battery first.
doing that wrong blows 1 to 5 fuses, even the 50 to 150 huge fuse
or worse worse, the 120amp fuseable link is blown. (this case)
blowing the up will make the new alt dead 2 ways
1: it can not connect to the battery lug Plus.
2: and worse yet the cluster lamp lies or acts dead. or lies.


xD specifics , reading the service manual to you now
the schematic speaks volumes if you looked
self contained regulator in side ALT, a good dead that.!

wow 5 fuses to blow up

a 60amp fuse blows
120amp fuse blows
the 120 blows if battery is not unplugged first
if blown alterator is now dead. (off line 100%)

t
the 120amp keeps from blowing up a battery if it shorts.*(and they do)
the 120amp also prevents alternator fire when those pesky 3 phase diode packs short out, fires near fuel are never ever fun.
there you go all causes and why.

a volt meter finds all this ,
measure all 5 fuseS see Nhear, 12vdc both ends of fuse or it IS BAD
13v to 15vdc engine running
but your car Alt is dead so voltage is 11 to 12vdc. and discharging fast
JUST ONE $15 METER AND OMG SEE THE TRUTH OF ALL THIS.
FAST/

NO ENGINE TOLD PETROL OR DIESEL OR SIZED
1.5, 1.6, 1.8L 2.0L
the words "the alternator", means nothing above.
IS REDONE MEAN THE SOUND SYSTEMS?

Did it mean changed it out/ Replaced it? ALTERNATOR>?????
and did so FAILING TO REMOVE THE NEGATIVE BATTERY LUG FIRST, IF YES, YOU BLEW OUT
THE HUGE 120AMP ALT. FUSE./ FOR SURE.

THE BATTERY IS ONLY WEAK BECAUSE THE ALTERNATOR IS DEAD.
1; ALL FUSES GOOD (NO)
2: FAN BELT TIGHT TO ALT.
3: ALL WIRES TO ALT GOOD, 2 SMALL ,ONE TIGHT

NEVER PLAY WITH THIS THIS LUG
BATTERY NEG LUG MUST BE DISCONNECTED FIRST


1.6L PETROL EXAMPLE.
AND when done the bottom connect seated.

Hi. Most of the larger fuses have a screw that goes into each leg of the fuse. Normally the fuse box will need to be removed slightly to access the screws. When they are removed the fuse shouldbpull out.

Did you replace the battery recently?
seem like your main fuse many may be 100 or 120amp fuse is blown and not powering little fuses.

does the car crank if not check battery and the big maix fuse usually 50amp or 120amp fuse either ecmbat fuse or ign fuse

blew main fuse normally around battery area

Hi,
I think the problem is not the alternator but the conection in the 120Amp fuse to the main engine fuse box.
The actual contacts to the spade fuse are enclosed and the contact area cannot be cleaned (scraped) easily. The fuse does not pull out like the rest but is bolted in with two bolts (one 8mm and one 10mm) No one knows this at first, release the bolts on either side and work the spade fuse up and down many times to score the contact area.
When I first tested it it was showing some 20 ohms with a high impedance meter but after it was cleaned it showed close enough to zero.
The high resistance connection on the 120Amp fuse may have caused a volt drop (with all systems on ie engine, air, wipers, and headlights) sufficient to drop out the engine relay and it conk it out. It starts again readily but the low voltage may cause the stop light warning light to come on.
Volvo had the car for two weeks and couln't fault it after I did the clean and replaced the engine relay - but they didn't charge me - so good on them. They quoted me $1400 to fit a new alternator saying they had seen the problem before and they replaced the alternator and the cable which may have inadvertantly fixed the bad connection on the 120Amp fuse.
I worked for Volvo Truck for a couple of years as a contract Production Engineer but when sales went down I was moved on - guess I was too much of a smart arse. Renault owns them now - predictable I should have thought.

It has to be either a fuse or the blower motor resistor.

you have to take out the fuse box it bolts from the bottom,be patient.

Check your coolant level sounds like it might be low.