truck wouldnt start. rare problem (solved)

[Dawa]

so this saturday i spent the afternoon dropping my stock 620 rear leaf springs

in order to swap em for the set of 720 leafs i had, in order to get ready for nissan jam.

 

well, as it turns out, sure you COULD use 620 bushings on 720 leafs but its a bitch so i said

fuck it and reinstalled the 620 leaf. 

 

went to start & move the truck and... nothing....

i installed a voltmeter and it wasnt even registering any voltage.

lights wouldnt come on, no radio, starter wouldnt make any sound.

 

so this is what i was working with: 

battery only a yearish old, starter and alt were both only a few months old.

checked the fuses within the car and the fuse between the batt and starter. 

all fuses were good. 

 

connected my battery tender and it showed solid red (meaning charging)

blinking green means 80% or higher and charging. 

 

ok maybe i left the light on or something and drained the battery the whole day?

 

sunday morning came, tried to jump the batt. nothing, again no voltage registering

left the battery on the charger overnight til it showed solid green (100%)

installed it monday morning, nothing. 

 

after work im checking and cleaning connections, etc. 

swapped in one of my other good batteries and nothing. 

 

i swapped out the 25amp fuse between the batt/starter with an 8a just to see if it would

start. it did, and blew the fuse. i was out of 25s so i put in a 30. 

 

disclaimer: i know that factory design is for a 20amp fusible link. 

 

 

long story short, it was the rare case of "fuse looks good but is blown" problem :/

 

which i think i had read about here. and if i hadnt, idk how long it woulda taken me 

to solve this riddle. 

 

[laotsu]

I had three corroded fuses when I first got my 521. I looked at em and wiggled em for nearly a year trying to deal with weird charging and light issues. I finally replaced all the fuses and cleaned the fuse block. All problems disappeared.

[MikeRL411]

That solder joint between the fusable link inside the glass tube and the tin cap will eventually get to you!  Vibration [what! in a 40 year old car or truck?] will eventually fatigue the connection.  It will probably even show continuity on a multimeter but won't pass more than a microamp before giving up the ghost.  As the owner of a 46 year old car, you don't have to ask how I know this.

[Dawa]

yeah thats what i was reading (that the fail can happen closer to the cap so that you cant see it)

didnt consider that vibration could do it in as well, but i believe it. 

fuse was few months old, btw. 

[laotsu]

good argument to upgrade to the spade style fuses

[MikeRL411]

yeah thats what i was reading (that the fail can happen closer to the cap so that you cant see it)

didnt consider that vibration could do it in as well, but i believe it. 

fuse was few months old, btw. 

 

 

The old Military Spec. was that you could not depend on a solder joint for structural integrity [strangely. but with predictable results often violated in modern satellite construction, I didn't allow it in my USNavy FLTSAT satellites, they were still operating after 25 years and replaced their follow-on satellites that failed on orbit] so the more modern fuse designs are a step in the right direction, they have welded connections.

[Dawa]

^interesting story.

 

ive thought of upgrading to spades, it would be pretty easy, but i like the nostalgia of the old fuse holder/box

[laotsu]

^ditto

[Z-train]

I use circuit breakers in spade fuse holders for the fusible links.