wiring tailights...keep burning out!

I am wiring my 47.Starting circuit done.now started on my tailights,as soon as I touch the hot to the wire that goes to the shortest of the 2 filaments in the bulb,it flashes and burns out..never to shine again.but the larger filament shines on....what gives.I am running the wire from the tailight screw on the switch.the switch has a 20 amp fuse incorporated.any ideas as to what is going on.

 

6 volt bulb? 12v battery?

 

Socket is shorting out?

 

No,brand new 12v bulbs,from Napa. Burned them
twice

 

if the socket was shorting..both filaments would pop.

 

Not necessarily. The bulb only draws amps when on. Short will draw amps over what the light needs when engaged in completing its circuit.

Wrong bulb? Shorter filament vs longer. Or wires crossed. Stop vs backup light? Still shouldn't burnout. huh. waiting on more brain power here on the hamb...

 

I wasn't sure from reading your description....but it sounds like you are getting both filaments illuminated (albeit momentarily) by touching one wire. If this were the case I wonder if you have a poor or no ground up to the bulb and thus causing a series circuit until elevated current fails the low resistance filament

 

Correct me if I'm wrong but if you didn't have a ground the light wouldn't even come on at all.

 

Best bet is to by p*** the bulbs for now and use a test ground (wire with two alligator clips) on the bulb housing or ground lead wire.
Then use your test light wired thru a voltage indicator to show how much and when you have juice.

I have found best practice is to test connections first, then add bulbs later.

 

Both filaments are not supposed to burn at the same time.One is for tail lites,the other for turn signal and brake lites.

 

Have you tested with a meter to see what voltage is being delivered to the socket? Probably not the problem, but it's the first thing I'd check.

 

If you put a 12volt bulb straight on a 12volt battery. It will light and not burn out. If you are overcharging your system (voltage regulator way off) you would be burning out more lights then that. My guess is still a short in the socket, being that the other filament doesn't burn out from voltage.

Fordtudor37 has it right. Meter time.

 

Can you elaborate how you are testing (in car, etc). A number 1157 bulb?

 

Some extra ideas to think about;
Lights go bad a lot,if =[solid motor]no rubber motor and tran mount and or no shocks in front,or too low* and car hits road bumps.

 

Some extra ideas to think about;
Lights go bad a lot,if =[solid motor]no rubber motor and tran mount and or no shocks in front,or too low* and car hits road bumps. headlight or tail light mounts are flimzzy and vib.

 

Are you testing it using a battery charger? or the car's battery?

 

Have the Napa guy test the bulb in the store. Bring your other bulbs and get a refund.

Obviously the bulbs can't handle 20 amps, as they blow before the fuse.

 

huh? that makes no sense at all.

 

thanks,l will check volts to pigtails later today.I am wiring from scratch.i have a 12 v battery.I am feeding the light switch off the ignition switch,constant hot,to the 20 amp fuse on the switch,wire to lights from twilight connection out to the tailights.I ground the housing via alligator clip then touch the wires and the short filam burns out.The bulbs are 12v dual sig/tail.This is getting intriguing.

 

This may be dumb, but are you sure you have the correct sockets for the bulbs(not running a single socket for a double bulb) Also being dumb here I'm ***uming you switched to a negative ground system?

 

Yes.all points covered

 

this is from some random answer type site, but it sounds about right:

Sylvania website says that the 1157 is a 26.9 watt bulb rated at 12.8 volts DC. Using simple math (V=I*R), we find that the amp draw is 2.1 amps DC.

It doesn't say which filament or if that's combined draw, but the point is it's low.​

I am just guessing that you may have another circuit seeking ground thru this light filament, and the other circuit loads this filament way past its amp capacity, but still under the 20 amp fuse capacity. The brighter filament has a greater amp capacity, so thru some quirky coincidence, your added load is over the small filament's capacity, yet under the larger filaments capacity. As stated above, it's meter time to unravel this one.

A quote from my old CC electrical instructor, Mr.Z: "Inside every electrical conductor there is a certain amount of smoke. Try not to let any out, as you can never get it all back in."

 

rodknocker is on target. Some 6V sockets won't work with 12V bulbs. Try a good 12V socket with two contacts. I had to change the sockets on my 35 Ford to newer 12V sockets. good luck

 

There is no way a 12v bulb should burn out if there is only 12v in the system, it doesn't matter what size fuse, or if anything else is drawing current thru it, or it's wired wrong, etc. It just won't happen.

Just for fun, connect one of the bulbs directly to the battery, see if it burns out.

 

My bet would be on a bad batch of Chinese bulbs. If all is as you have described, the small filament is wrong. Try one of these bulbs in a car that takes the same bulb. If it is 1157, they are used everywhere, almost.

There is nothing you can do with a single 12v source to burn either filament on a good bulb. Place the filaments in series, run them both a once, it won't burn them.

 

this is my thoughts too. but i'm inclined to think that weldtoride might be on the right track too. if something else is drawing a lot more power thru the filiment, that might be your problem.

 

It sounds like you are seeing both filaments illuminate at the same time (until one burns out). The ground is common, but are you connecting both filaments at the same time?

 

Is that alligator clip giving a good ground ? "Bad" grounds can give you more electrical headaches than anything. Get a very solid ground connection established,....then check the rest. Learned that the hard way.....

Happy Roddin' !!!!!!! 4TTRUK

 

It wouldn't matter. They are both on when you step on the brake & have the tail lights on.

It doesn't matter if it is drawing through something else. It all operates according to Ohms Law. The voltage (12) is distributed across all the things in the circuit. Each one will draw only what its voltage drop & resistance will allow. The whole thing (circuit) is self limiting. Anything else in the circuit will reduce the voltage available to the filament, and thereby the current through the filament. The highest resistance ( the bulb filament) will draw the least current which limits the current in the entire circuit.

 

it does in fact matter if both filaments are being illuminated at once. If 12v is erroneously being applied across both terminals instead of individually during his test, then only the high resistance filament will light....the other .7-.8 ohm filament is backfed and becomes the circuit ground. I just verified this wilth a spare #1157 ( 7-.8 low resistance, 2.3 ohm high resistance). The intended ground is obviously the bulb outer base