Blowing main fuse

[woodchk502]

I keep blowing the 25amp main fuse on my '72 HEI convert, but going between positive batter terminal and a power distribution block on the driver side. Thinking it could be ground related, but not sure. Seems as though it will idle with no issues, rev it and it blows making me think alternator is over charging. Below truck porn is so yall will help.

 

[woodchk502]

Well, just cleaned main ground and all others that I could find. Except body to engine strap, fired it up and fuse blew immediately.

 

[sponsoredbydad]

Multi meter-Test alt output to battery while idle, then rev it up and watch it. Could be the internal regulator Not exactly sure what you are saying. Is there a separate fuse going to the power block that is blowing? If that's the case disconnect everything going to the power block then touch each thing 1 by 1 till it blows that way you will know which wire is causing the short. wiring is a slow tedious job so you just have to play the elimination game either manually or with a multi meter.
PS the porn is good but a pick of the wiring block, alt and battery might help out a bit more

 

[woodchk502]

SBD, sorry for the terrible post. I am out of town, with limited Internet. I will try to get some pics and get them uploaded. I did put a 30A in it, and it held to get me back to the campsite last night, not a great idea I know but sleeping in the woods with my 3 kids wasn't either.

 

[diesel4me]

When I had a few first generation K5's,I found two "hidden" fuses in a wire that was routed along the upper radiator support--it had two rubber fuse holders that looked just like the connector in the license plate harness in the rear,that you pop apart,inside were a short glass fuse.one on each front corner of the nose near the fenders--
...both were green with corrosion,and blown!..when I cut the fuse holders out and spliced new ones in,my amp meter suddenly worked again,which had never worked before since I owned the truck--and I noticed the headlamps were now brighter too at night..

Maybe that wire has shorted out along its route somewhere or those fuses are all gangrene or something..

 

[woodchk502]

Multi meter-Test alt output to battery while idle, then rev it up and watch it. Could be the internal regulator Not exactly sure what you are saying. Is there a separate fuse going to the power block that is blowing? If that's the case disconnect everything going to the power block then touch each thing 1 by 1 till it blows that way you will know which wire is causing the short. wiring is a slow tedious job so you just have to play the elimination game either manually or with a multi meter.
PS the porn is good but a pick of the wiring block, alt and battery might help out a bit more

Ok, I just got back in town with decent internet, and am able to post. After thinking about this a bit, I did not have the problem until I replaced both battery cables. My battery has both posts, so opted for the side post cables.
You will notice the questionable fuse in this pic and a distribution block that it goes to.



From the distribution block you see a red wire going across the core support, and another wire with the mini glass fuse Diesel4me mentioned (it was good)



from there it goes to the below block (this was supposed to be temporary but like most things fell by the wayside) you will see that two wires leave and go to the alternator, and a third goes to a mess of wires near the DS headlight.



Here they are going into the alt.



and down into the headlight fiasco, where low and behold the other mini fuse was blown. I replaced it but it mad no difference, though some time ago I found the PS mini fuse blown and the truck would not start I find that a bit curious.



I will also add that when I first put the 30a fuse in, it lasted over the course of 4-5 startups. But now it does not matter 30a on down blow as soon as the truck is running 1-2 seconds max. You can tell when it blows, the interior light brightens, then goes back to normal. No issues while its running everything works (well every thing that normally does). There is just no power for a start.

SPD I also, pulled every fuse and wire from the fuse box, except the main feed coming in to power the ignition, it still blew right away, one other thing that I noticed is that after the fuse blows, the tach needle fluctuates erratically. So I guess after a few days checking, and just dealing with it so that the kids and I could enjoy some time away we still have an issue. Any ideas, I am hoping the masses can help, we need some action in the first gen forum.

 

[bigblock72]

Originally the wire from the battery to the distribution block was a 14-16 gauge fusible link, which is roughly a 50 amp slow blow fuse. I would recommend either putting a fusible link back in or wiring in a 50-60 amp fuse with 8-10 gauge wire.

Check to make sure the alternator is charging no more than 14.6 volts.

The little inline fuses at the corners of the radiator support are for the ammeter and won't affect anything else.

 

[woodchk502]

Originally the wire from the battery to the distribution block was a 14-16 gauge fusible link, which is roughly a 50 amp slow blow fuse. I would recommend either putting a fusible link back in or wiring in a 50-60 amp fuse with 8-10 gauge wire.

Check to make sure the alternator is charging no more than 14.6 volts.

The little inline fuses at the corners of the radiator support are for the ammeter and won't affect anything else.

Please explain if you would the reasoning behind 14-16gauge with a fusible link, and a 8-10 with a 50-60amp fuse.....

IIRC i copied the original (what was there is a more accurate statement)wiring setup as far as the 25a fuse. excepting that I used 10g oil resistant wire instead of the 14/16. I could be wrong by using the 25a fuse, but i believe it was what was there. Keep the feedback coming.....
guess I should get a Haynes manual or something for the wiring diagrams...

 

[bigblock72]

The fusible link needs to be 2 sizes smaller than the wire it is protecting. i.e. 14 guage to protect 10 guage, 16 guage to protect a 12 guage.

The reason for the bigger wire with a regular fuse is so the wire at the terminal of the fuse doesn't get hot and melt and prevent the fuse from doing it's job.

The alternator will charge up to 60 amps and will blow a 30 amp fuse within minutes or almost instantly if the battery is low. All of the accessories, lights, etc. will easily draw 45ish amps, so I have no idea how a 30 amp fuse ever worked. I would just install a new fusible link and be done with it.

Don't bother buying any books for the wiring diagram as they don't come with anything useful.

Where does the black wire in post #6 go?

 

[woodchk502]

Makes sense on the wire size, just not sure why mine is/was set up the way it is. As for the black wire

A&B



A goes from the battery to the ps inner fender as a ground.
B goes from the distribution block out to the small glass fuse on the passenger side. the ammeter fuse.... and why are there two of these little bastads?

 

[Kain]

its hard to see in the pic, is your ground cable cracked in the coting on it?
if so corosion could have got to it

 

[woodchk502]

its hard to see in the pic, is your ground cable cracked in the coting on it?
if so corosion could have got to it

Main cable? no way, they are a week old. But the small one, I will double check....

 

[Kain]

the one that connects to the fender on mine was slimy on the inside of the wire

 

[woodchk502]

the one that connects to the fender on mine was slimy on the inside of the wire

No issues there, mine looks good.

Does anyone have pics of what the wiring on this side looks like fusible link etc....

 

[diesel4me]

I do,but I tried to scan the diagram and it comes out too small and blurry to be of any use to you--maybe try google images,I have found good wiring diagrams that way before,ones either in GM service manuals or Haynes,etc..sometimes another forum member has posted them on another site and you can locate it by googling..

 

[woodchk502]

I do,but I tried to scan the diagram and it comes out too small and blurry to be of any use to you--maybe try google images,I have found good wiring diagrams that way before,ones either in GM service manuals or Haynes,etc..sometimes another forum member has posted them on another site and you can locate it by googling..

Thanks for trying, I have a really ice color coded one, I just wanted to see what the actual link looks like, and how it was all routed. I'm a visual guy, not real book smart.

 

[ekajkrats]

I'm pretty sure it just goes from the battery positive directly to the terminal on your fender. That's how mine was from the PO and how I installed mine after that one blew.

Here is a photo of fusible link wire I bought at Napa and just added terminals to make it work:

Looking closely at it and touching it, it has a powdery residue on the outside.

I can show you a picture of how mine is currently, but it's setup how I described, and I'm a hack

-Jacob

 

[woodchk502]

Well Advanced Auto is the closest to me, tried there for the link.........

Stupid lady told me to try Best Buy or Radio shack

Not sure how these places have become so widespread, most people working there are somewhere between no help and a hindrance.

Off to NAPA tomorrow.


And as an extra kick in the jewels I noticed the gas gauge went nuts on the drive to the parts store, I hope it is because the main fuse popped, and not the result of something else going on.

 

[diesel4me]

I find I often have to look up the part numbers I want of just about anything,and ask for that number specifically,in order to get it from any of the "non jobber" parts stores like Autozone,Advanced Auto,etc...especially things like that fusible link wire,which most likely only an older,experienced parts counterman would know about..the guys who don't give you the "blank stare"..

--(and sadly NAPA is about the last jobber store locally, who'll actually hire a good counterman with years of experience,and isn't afraid to open a catalog,instead of a fresh out of high school kid who's only good at pressing buttons,and cant look up anything "not listed in the computer".. --but they charge a much higher price for that "service" too--too bad the counterman who deserves some of that extra money never sees it in his paycheck.. )..

 

[woodchk502]

I'm pretty sure it just goes from the battery positive directly to the terminal on your fender. That's how mine was from the PO and how I installed mine after that one blew.

Here is a photo of fusible link wire I bought at Napa and just added terminals to make it work:

Looking closely at it and touching it, it has a powdery residue on the outside.

I can show you a picture of how mine is currently, but it's setup how I described, and I'm a hack

-Jacob

Well,
we are operational. I went with 14g fusible, since my main is 10g. Thanks for all the help guys.

Now on to the other wiring nightmares this thing has........