blowing 20a fusible link

[56hotrodred]

I have been trying to troubleshoot an electrical problem that when I pull headlight switch it blows my 20a fusible link.

I have been rewiring my rear harness and have a couple of issues there but it is now disconnected until I figure out what I have done up front.

Can I start pulling bulbs or disconnecting things like the wiper switch to see what is blowing the fuse?

I have replaced the headlight switch, put the old one back in and it still blows.

Thanks in advance.

Barry

[Desert1957]

I would try and isolate your problem first. Make up a jumper lead with a replaceable fuse for testing only.

The built in circuit breaker in the headlight switch gets its feed from the link. If that's the link blowing, try unplugging the wiring bulkhead connector at the firewall for the headlight harness. If the fuse doesn't blow then you know its that section of harness.

If that doesn't work try and isolate the rear sections until your link stays intact. Make sure using a wiring schematic what that link is feeding, It might also feed some area of the fuse panel that's 12 volt hot all the time.

Only as a LAST resort , you can trace every wire from your headlight switch but from your post the rear wiring you have repaired is fused in the panel which would not cause the fusible link issues you have.

Be patient , you will find your problem.

Desert

[silvereagle07]

What year is your truck? That would help with looking up the diagram. But something is shorted to ground. I agree with Desert1957. Isolate the problem first with replaceable fuse for testing.

[56hotrodred]

The truck is a 1973 1/2 ton 4x4.

I have disconnected the entire new rear harness. With that disconnected it should not be causing any issues should it?

I am not sure I understand how to "make a jumper lead with a replaceable link" and then do testing!!!

I really appreciate your attempts to help me through this little issue.

Barry

[Desert1957]

Originally Posted by 56hotrodred

The truck is a 1973 1/2 ton 4x4.

I have disconnected the entire new rear harness. With that disconnected it should not be causing any issues should it?

I am not sure I understand how to "make a jumper lead with a replaceable link" and then do testing!!!

I really appreciate your attempts to help me through this little issue.

Barry

Use two small alligator clips, a small section of 12 or 14 gauge automotive wire with a replaceable inline fuse in the middle. Connect all this together and clip it inline where your fusible link would normaly be.

It allows testing with fuse protection, If you really want to get more fancy you can install a circuit breaker instead of a fuse.


Desert

[56hotrodred]

I actually replaced the old-style in line fuse with a replaceable one earlier. It is on the lower right side fairly close to starter.

It is this easily replaceable fuse that keeps blowing when I pull the light switch on. Just got a chance to see the picture you provided and it is exactly you show. I actually had pretty much all things working in the front before except the right signal light... I wonder if that is causing me problems???

Also as said I have the rear harness disconnected and I still have to finish the trailer wiring. So this is out!

So in my way of thinking, please correct me if I am wrong, it has to be in the front lights or under the dash and it should be a hot wire touching the frame, body or something! Does that sound right?

Again continued thanks I have always struggled with things electrical...

Barry

[silvereagle07]

Using inline fuses as permanent solutions would not be a good idea for wiring system. The fusible link can handle sudden current spike when fuses will blow. Thats why they are used for wiring systems instead of individual circuits like fuses. If you think it is the front turn signal issue diconnect it and retest the fuse. You have a power wire short to ground. Find the short, repair it and get a fusible link to replace that inline fuse. One thing I use in the fuse location to find shorts is get simple light bulb like an 1156 and use it while you are tracing the wiring for hard to find shorts. With power off, insert the bulb wires in place of the fuse. Wiggle circuit and if the light goes out you'll find the short. I do it in fuse boxes all the time. Saves a bunc of time. Good luck .

[56hotrodred]

I did not know that could be an issue. I would have done it on the advice of someone else and actually replaced the rather large fusible link with 2 in-line fuses. If I recall I had a hard time finding one of those big original style fusible links that pretty much came right off the starter.

Sounds like, by what you say, it would have a propensity to blow more with what I have done. So maybe not safety issue but more of a pain in the ass thing if they keep blowing.

I am going to start by pulling bulb out of right signal light and pull the light switch to see what happens. If it does not blow then I have narrowed it down.

I am interested in hearing more about my replacing the large fusible link with 2 in-line fuses if anybody has any comments.

Barry

[Desert1957]

Like I mentioned above, The "Inline Fuse" thing is for testing. After you repair your short to ground, replace with a section of fusible link.

Didn't know this was going to turn into a "What is right and what is wrong " thread.

Just trying to get the man started in the right direction

[56hotrodred]

Hey so sorry not trying to turn this into any kind of thread just looking for and obviously needing assistance!

I was given advice, that now sounds like not so good, from somewhere to put the inline fuses (x2) in place of the original fusible link.

Could you please post a picture of a modern replacement fusible?

I am pretty sure that the local NAPA store were the ones who said they don't have the original fusible links anymore and to use these (in line fuses)... Maybe they just did not want to look it up. I think I kind of drive them crazy as I have several projects on the go and they are often vehicles with several years of parts in them... hard for them to look it up!

Anyway I am going to use the in line fuse as you suggest, I have bought more fuses, and see what I can find out.

Thanks again to all,

Barry

[56hotrodred]

I just realized that the "Title" of my first post on this topic was wrong. As you now know I keep blowing a 20a in-line fuse that replaced the original fusible link... old title "blowing 20a fusible link" with new title "blowing 20a in-line fuse."

I have changed the Title but am not sure if this changes threads now or what. Lets see what happens - hope I don't loose anyone because I am learning things here.

Barry

[Desert1957]

Any update?

Curious to know if you found your shorted wire.

Anyway, after you find your problem here are some common areas to find fusible links.



also here is a source for the replacement links

http://www.madelectrical.com/catalog/fusible-link.shtml

Desert

[56hotrodred]

No not yet I had to go out of province for work related meetings but am hoping to get back at it this weekend.

Thanks for the link.

Barry

[wilkin250r]

I would agree that an inline fuse is a great TESTING tool. I know I certainly wouldn't want to blow seven or eight fusible links while I was looking for the problem.

I didn't see anywhere that it was suggested as a permanent solution. Once the problem circuit is located and repaired, then obviously the correct permanent solution would be a new fusible link.