Headlight fuse pops when I "get on it"

sorry, i should have said that the current through the fuse would have to drop.

 

I guess by now I should know better than to reply to posts, using information based on time-proven laws of physics as they relate to electricity. EE degree, and over 35 years in the business, including a lot of circuit design, so I have nothing to prove to myself. I sure wish there was an easy way to convince people that their understanding of circuitry is wrong.

Henceforth, I'll refrain from having a battle of electrical theory with those who are unarmed.

 

Sorry, you should have said that the current through the fuse would have to RISE. (not drop)

Unless you change the resistance, if the voltage goes up, the current goes UP, not DOWN, in the whole circuit, including the fuse.

You see, if there are more volt guys pushing the amp guys past the ohm guy, but don't add more ohm guys, it builds up so much friction that the ohm guy overheats and burns out. Only then will the circuit open and cause the current to drop.

You, like so many people, seem to be confusing amps with power.
If you increase the volts, AND the RESISTANCE to keep the same POWER, (watts) THEN and ONLY THEN will you have a drop in current, but it is from the increase in resistance, not the increased voltage.

Hey Ebbspeed, an armed society is a... oh, never mind!
30 years building hospitals, auto plants and Nuke plants for me.
Well you can figure out who actually knows something about REAL WORLD electricity and who throws out something they overheard down at the gas station...

 

i guess i am the guy in the garage they keep talking about.
i was wrong, i am sorry if i steered any body wrong.

 

No harm in it, none of us understand everything, and electrical stuff seems to be one of the most confusing. My nemesis is automatic transmissions, tried to rebuild one and screwed it up royally. Twice. The third time I paid somebody to get it right.

Kudos to you for the post! You have my respect for doing it. A lot of folks would start a pissing match.

 

Man I'm Tired

 

As a bulb gets brighter via higher voltage, the pipe gets smaller. Marginal, yes,, but its the truth. I can hook a amp gauge and make a video if anyone would like proof. Now, I am not trying to say this is the problem, it probably isn't, I was mearly trying to make a suggestion for the slim chance it might be.

 

If a 20 amp and a 25 amp fuse both hold under normal conditions but suddenly blow when you get on it, it's probably not an over-voltage problem. I would look for a bare, pinched, or chaffed wire that can move when you get on it. It could be inside the wiring loom or in those new headlight buckets or even behind the fuse block. I would start at the new headlights.


Don't feel bad about the ohms law thing, I had a hard time understanding it once too.
Much of the confusion comes from things like dual voltage motors. We know that they draw less current at the higher voltage, but we often forget that before we can increase the voltage, we must first rewire them to increase their resistance. It's this increased resistance that causes the amps to drop.

 

That pipe gets smaller at a much slower rate than the increase in amps or the bulb wouldn't get brighter in the first place.

 

Good advice. If the harness you have there is out of a later GM product, IIRC the purple wire is a main feed wire. You'd have to look at a '65 or so Chevy schematic to gain some insight.

I also agree with the wiggle test of every wire with the lights on, even under the dash and firewall pass-thrus. Make sure everything has sufficient strain relief and tie that engine down.

Bob

 

Nothing wrong with crimped terminals if crimped correctly, I've never had one come off, Soldering isn't advised as you cannot control the flow of solder up the wire which will result in a stiff wire that can fracture due to any vibration.

 

Crimp terminals are used in more places than you can imagine. The problem is that too many people crimp them with dykes and wonder why they fail.

Soldering is fine, provided you tin the wire properly and of course remove the residual flux. Soldered connections rely on sufficient strain relief to take the stress off the soldered joint. Any wire connection should be strain relieved, regardless.

Soldering is just too much like work for me. Buy the right assortment of good crimp terminals and crimper and it'll last forever.

Bob

 

when I have an intermittent short to ground, which is clearly what you have I start breaking the circuit down until it goes away. example, disconnect one headlamp at a time. if fuse still blows start disconnecting at the switch. it should become pretty clear what circuit is causing your problem. no way overcharging or high resistance will cause a fuse to blow just my 3 cents

 

If you are using a parts store crimper, throw it away.

I use one of these: http://www.carid.com/universal-igni...&cagpspn=pla&gclid=CP-bueK-2boCFWqCQgod80sA_A

Between using that, and the connectors that are heat-shrink, I have not had a crimp fail in about a decade.

I have only been able to sell one customer on soldering a whole wiring harness, over the same period. Once I give them the estimate, they refuse.

 

Since this thread has been resurrected after 6 months was the problem ever resolved? HRP

 

Well HRP, started out by fixing the motor mount problem, installed a set of solids. Then I tried wiring the purple wire back to the other post on the starter. This made my alternator hot to the touch even when the car wasn't running and of course ran my battery dead, so I unhooked it again. Then I installed new aluminum radiator and bigger electric fan to help my cooling issues and as soon as I turned on the fan popped the fuse again.....hmmmmm. So I threw a 30amp fuse in it just to see if my fan would work and it seems to have done fine ever since. Even got on it one night and headlights stayed on. Then a couple weeks ago I was driving it during the day and the car just shut off like you turned the key off, car would turn over just not start, checked the fuse and sure enough blown. Put in another 30 and been driving that way ever since. So really problem hasn't been fixed correctly yet, just a band aid fix of a bigger fuse. Maybe I'll figure it out over the winter, my uncle is an electrician might have him look at it or just rewire the whole damn thing I don't know????

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Without re reading the thread..make sure the wire the fuse is on is rated for at least that size of fuse in regards to gauge and length.

Otherwise the fuse may notice blow, the wire and then car may catch on fire......

 

Yeah yeah don't rub it in.....

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Not trying to rub it in..just sometimes the younger guys need to listen to some of us "OLD" fuckers

 

Are the headlights Halogen? If so would a relay be needed to take the voltage off the switch? Pete

 

Yep, using a too high rated fuse sounds like a fire waiting to happen. I am constantly amazed by the uninformed risks that people take which might result in the total loss of their ride. As for crimped terminals, I have been using the same Bosch crimper I bought in Germany for over 40 years and yet to find anything else that comes close to it....

 

It's not uncommon for an electric fan to pull 30 amps plus on startup so a 30 amp fuse could be marginal, also do you have a relay on the fan ???

 

Replace that 30 amp fuse with a 20 amp fuse before you burn it up, then have "someone knowledgeable" find the short.
Band aids are for boo boos.
Poor electrical work causes boo boos.

 

So, you have a 30 amp+ draw from a cooling fan and the headlights are on the same circuit?

My original opinion was the short to ground like many others have said. But, you certainly could be overloading the circuit (fuse) with that arrangement.

The headlights and fan should be on separate circuits and the fan should be on a relay. I might even consider putting the headlights on their own relay.

 

Yes! Use a separate relay for both. Also many fans need a 30 amp fuse.
I didn't like that red coupe picture!

 

Well to ease everyones mind she's been put away for the winter so there will be no erupting fireballs. Guess that will be one of the winter projects to figure out. Thanks to everyone for their comments and advice, good, bad, and ugly.

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I'm having a very similar problem with my '67 Land Rover. Nearly identical symptoms so I won't restate them. Thing is my fan had been added over a month earlier with no problems. Fixed a frayed wire which I thought was the culprit but happened again. This time I pulled the alternator and had it tested. Turned out it was overvolting at 15.5. Ordered a new one. Will update on result.

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