Headlights blow'n a fuse?

Can a bad headlight bulb blow a fuse?

A 30 amp Fuse pops about 3 minutes after I put a new fuse in. I've isolated the problem from the line out of the switch direct to the headlight (no hi-low switch). The line dosnt seem to have a short in it but then again I dont have a voltage tester handy to see the draw. headlights are about 10 years old too. Nice street roddy wiring but it is 20 years old. Hate to yank it all but thought Id ask before I get into a wiring mess.

C.

 

I had a headlite have a carbon trail when I would hit the high beams it would blow a fuse. took awhile to find that short

 

Try it with one head light removed then the outher.

 

Y ou didn't say what headlights you have but the the ones in my daily have H-4 halogens and they tend to draw a lot more power than the old lights. I'm going to install relays to take some of the load of the headlight and dimmer switch.

 

Remember, fuses are intended to cover double what the "normal" amp load of a circuit would be in case of a surge. If you headlight circuit was designed originally with a 30 amp fuse to protect it, then it was intended to normally carry 15 amps. I'm talking wire gauge here. Blowing that 30 then would mean you are way over loading that circuit, more than double.

Relays are a much better idea when carrying higher loads. Saves the circuit from over loading and the contact points in the switches from over arcing/melting/burning. Also install a circuit breaker in the battery feed side to the relay and make sure to gauge the wire heavy enough to handle the load.

Just a thought, is it possible you have two or more accessories running off that same fuse, possibly with them all on at the same time, then the circuit is overloaded?

 

12v headlights shouldn't draw enough current to pop a 30amp fuse, and you say the fuse doesn't pop instantly, so thta kinda rules out a dead short. I'd suspect heavy resistence in the circuit somewhere...generally from a poor or dirty connection, poor ground, corroded wire, too small (gauge) of a wire, or multiple circuits drawing power from the fuse in question (as mentioned in another reply).

To give you an idea of how much curent draw there ought ta be, when I rewired CathyH's 51 Mercury last year, I was curious to see how much power both headlamps drew, so I hooked an ammeter up in place of the fuse temporarily and tried out the headlamps on Lo and Hi to see what the reading was. On Lo, they drew 5 amps combined. On Hi, it was just shy of 10 amps combined. That's with all new wiring, switches, connectors, good grounds and all points of contact coated with No-Ox-Id protectant, and with brand new 12v lamps. I installed a 20 amp fuse in that circuit and it's never been an issue.

 

Exactly.

 

Fat Hack has some valid points....Do what he says and you should find the problem.
Glenn

 

i only use a 15 amp fuse on headlights...if you are blowing a 30 amp there must be a problem. i'd try replacing your headlight and dimmer switches..i've seen them go bad

 

Got it fixed! I was digging around the harness and found I also ran a heavy "emergency" wire for a later add ons or in case something went bad. replaced both headlights as well, lights running fine on 15 amp fuse.

Thanks for all the info.