dumb fuse question

[david42]

Hi all,

Been a while since I posted... just been enjoying the car! ('67 Monaco.) But now I have a problem (which will show you how new I am to classic cars): I need to replace the 20a fuse for the brake lights. I assume it should use a "fast blow" fuse instead of a "slow" one. But I figured I should ask here before I screw around with electricity.

Thanks,
David

 

[BJS racing]

yes your standard fuse in the fuse block is going to be a "fast blow" fuse. Slow blow types are more like fuseable link that is on main power wires going to direct battery sources. Your car has the glass fuses in it and they are all the same.

 

[david42]

Perfect, thanks!

 

[david42]

So this is kind of weird: Before I buy new fuses, I pulled out the blown fuse with the idea of testing it using one of the other working fuses. I figured I would just swap in the radio fuse and see if it works. Well, the fuse from the radio blew out as soon as I hit the brake pedal.

But then I noticed that the original brake light fuse was 10 amps, and the radio fuse was 5 amps. The fuse box label says the brake lights circuit is supposed to use a 20a fuse... in fact, I think all the circuits are supposed to be 20a (some of the labels are pretty worn, but I'm pretty sure they all say "20A").

So: is there any reason why someone would purposely used lower-rated fuses? Again, I'd rather ask a dumb question than accidentally fry something.

Thanks,
David

 

[BJS racing]

There is a reason and usually the answer is not one you want to hear though. It is usually means that someone has added something to a circuit or that they were having problems with the correct fuse and found that going up to that size didn't blow the fuse. If you run into what you have run into the first thing I do is go and look at all of the wiring specially up under the dash and see how much of it has been "repaired" or modified. Then you have to start checking to see if there is resistance in the harness on the circuits affected.

 

[Big_John]

The fuses were replaced with a lower amperage rating, not the other way around. LOL!

To me it shows that someone didn't have the right size fuses and just put in what they had. No harm in this.. Just the fuse will "blow" at a lower current draw and that can be a pain in the butt.

Go buy an assortment or two of glass fuses and replace them with the correct rating.

 

[BJS racing]

The fuses were replaced with a lower amperage rating, not the other way around. LOL!

To me it shows that someone didn't have the right size fuses and just put in what they had. No harm in this.. Just the fuse will "blow" at a lower current draw and that can be a pain in the butt.

Go buy an assortment or two of glass fuses and replace them with the correct rating.

You were right. Sorry man. Thats what I get for trying to respond to someone on here while answering a tech call here at work. Guess my brain can't process like it used to! But Big_John is right. That might be why you are having the trouble you are having because someone put a fuse in that was too small for everything running off of it. Damn I feel like a dumb *** right now!:toilet04:

 

[david42]

Thanks guys, that's very helpful. (Sometimes you have to troubleshoot the troubleshooting...)

 

[commando1]

. Thats what I get for trying to respond to someone on here while answering a tech call here at work.

I'd love to hear the solution you gave to the caller...

 

[70NPORT]

I always keep two or three packs of 20A fuses in the glove box just in case. Brand new haven't used them yet, but you never know. Also keep a fusible link handy. I don't like flatbeds.

 

[Big_John]

I always keep two or three packs of 20A fuses in the glove box just in case. Brand new haven't used them yet, but you never know. Also keep a fusible link handy. I don't like flatbeds.

Just wrap the old fuse in the foil from a pack of cigarettes..........

Seriously, get some 5 and 10 amp fuses too.

 

[bulldogchesty]

I have used the foil from chewing gum to get home.

 

[70NPORT]

Just wrap the old fuse in the foil from a pack of cigarettes..........

Seriously, get some 5 and 10 amp fuses too.

Now THAT's something I've never seen before....tin foil wrapped around old fuse. Gotta try that some time. Kidding.

 

[bulldogchesty]

Only to get home. Could cause a fire.

 

[Big_John]

Yea... but then you kind of forget about it.... and a couple years later you are under the dash and look at the fuse block and say "Oh yeah... I was going to fix that"

Not that I've ever done that myself... Oh no, not me.... I would never do that......

 

[70NPORT]

Only to get home. Could cause a fire.

That's why you keep extra fuses on hand.

 

[commando1]

Before our trucks starting coming with circuit breakers, ever driver always carried one of the "100 amperes" in their bag to get them to them home at 2:00 AM.

When it's 5 degrees out, screw the truck.........