I don't think having LEDs and incandescents together would cause your problem. More likely it's the bad switch or the wiring.

As for the fuse taking a while to blow, they might be what's called slow-blowing fuses that are designed to do that.

I had a problem with my dome light fuse blowing after I installed my trunk light. I wired it up to the same circuit and it kept blowing on me at what seemed like completely random times. It turned out that I ran the trunk wire across the dash too close to the wiper arms and when I ran the wipers it would rub against the wire and short it out. Those things move a lot more than you think.

I'd start by unplugging anything that runs on that circuit and start plugging them back in one at a time and monitoring the load across the fuse. It would probably help too to clean the fuse contacts (since they're probably rusty) and replace the switch just for good measure.

 

From a troubleshooting standpoint, I suggest you remove all courtesy bulbs on that circuit and open the door to allow power to run into the circuit. If the fuse blows it is the wiring/connectors/light sockets. I would then isolate all sections of the circuit by unplugging everything and then systematically reconnect one plug at a time to ferret out the short.
If all is well, next try each light socket one at a time to see if they are shorted out. If all is good there, I suggest you focus on the bulbs, again one by one to make sure one is not internally shorted out. If the short has not revealed itself by then, I suggest you trace all wires in that circuit to see if any one of them is plugged into a ground wire from another circuit.

Bad grounds are often the problem when turn signals, brake lights, and tail lights are not grounded correctly and are seeking a ground by back flowing through a bulb in a different circuit. Lastly, keep in mind that the cigarette lighter socket is isolated from the body of the lighter by a thin piece of cardboard. If that cardboard is not positioned correctly, you will blow fuses regularly. Good luck.

 

You have too much on the circuit. There’s a time inverse of how long it takes for a fuse to blow. Short circuit, micro seconds, a slight overload could take a hour or more. Depends on just how much you are over. Drawing 7 amps on a 7 amp fuse will never blow. 7.1 amps could take a half hour

 

Thanks guys for all the help! i put the ground clip of a test light on the negative cable and put the test light to the negative battery post. Sure enough the light came on, which means a short. I systematically unplugged things one by one until the light went off. I found the culprit! a bad glove box courtesy light switch. I unplugged that and plugged everything else back in and the fuse has yet to blow. the switch had large piece of exposed wire. I'm ordering one from national parts depot. I'm just relieved it was not in the door lights.....that would have been a pain. Phew! the good thing about challenges is that i learned something new about troubleshooting. I'm hoping this will cure the problem and the fuse won't blow later.

thanks again for the advice.

Mike

 

Hi Mikeg256 - I'm a newbie having electrical problems. The 7.5A fuse keeps blowing for the interior lights on my 66 Mustang convertible. While looking for clues on the forum I came across this thread that I found very interesting but confused my old feeble mind. You said
"I put the ground clip of a test light on the negative cable and put the test light to the negative battery post. Sure enough the light came on, which means a short".
To me the negative cable and negative on the battery post would be the same. Could you please explain?
Any information you can provide would be greatly appreciated.

Thank you,
Thom