fuse size instead of fusible link(s)

[Luvlegs]

72 C-10 - I-6

Starting over - found an old post I'd made - geesch - memory is going!

Have 20 amp fuse instead of fusible link - truck starts - fuse blows - stays running and everything works.

Been through all the "electrical" and "shorts" posts - can't find anything similiar - Rang out all the wiring - no shorts -

Ringing to ground - red wire - when key is on - even with voltage regulator unhooked - all good at back of ignition (took it out to check even).

Any idea where to start next? Am I just under fused at 20A (fusible link was 14A)?

[kbs71]

Defenition of a fusable link
"A fusible link is a protective device used in an electrical circuit and acts very much like a standard fuse. The major difference lies in that fusible links are larger and capable of conducting higher amperages than most fuses. When the current increases beyond the rated amperage for a given link, the fusible metal of the wire link will melt, thus breaking the electrical circuit and preventing further damage to any other components or wiring. Whenever a fusible link is melted because of a short circuit, correct the cause before installing a new one".
Most fusable links are 4 wire sizes smaller than the wire they are protecting. So either you don't have a big enough fuse, or the over voltage condiiton that your experencing is lasting long enough to blow the fuse, but not melt the fusable link.
What size fuse were you using?
Where in the electrical system are your fuses located?
What electrical mods have you done?
Heres a schematic for how a relayed set of headlights should be.

[kbs71]

I was downloading that schematic when you updated your post. I would think you'd need a 50 amp fuse as the main power fuse. Shoot just add up the amp of all you fuses under the dash. I think they add up to a little over 60 amps.

[kbs71]

Heres a picture of a labeled fuse holder for our trucks. I counted @ 89 amps in the entire fuse block. I still believe 50 amps should be sufficent.
http://67-72chevytrucks.com/vboard/s...d.php?t=177316

[Luvlegs]

HOLY CAMOLEE'! I had no idea - mainly because I thought the original fusible links were only rated at 14A....? OK, now I have to relook at the relays for the headlights.... I'm 99% certain I have what's in the diagram you posted (thanks) - but, I've been mistaken before... I'll be back....

[neonlarry]

They use fusible links for a purpose. A fusible link will withstand a momentary surge in current and not burn out it takes a sustained short before they will do that. With a fuse a momentary increase in current is enough to blow it. If you put in a fuse big enough to withstand the highest momentary current you might experience it would allow too much current to protect some of you electrical components.