Headlights blowing fuses

Nuzzy · Apr 14, 2009

Alright, help me out here...

The way I have my headlights now wired on the jeep is apparently causing problems. Previously, I had a standard 30a automotive relay from Autozone wired in to power the headlights. A powered switch in the dash triggered the coil and the lights did work for a bit. However they blew within a few minutes and since I hadn't wired in a fuse before the relay, the relay fried also taking out one headlight bulb. I thought at the time it was due to a short in the plug on the back of the lights because I could see wisps of smoke there after it fried.

So fast forward to today. I grabbed new bulbs (well new headlights really since they are the sealed beam disposable ones) and a new 30a relay like before and went to work. I have the high power lead from the batt fused with a 30a before the relay. Power is coming from the dash switch as it should, and the relay is grounded well. The high power output is running into the passenger light and then over to the driver. All wiring is brand new 12 gauge.

However, tonight I drove the jeep out to test the lights and sure enough, after 5-10 minutes, the headlights went out. The inline high power lead fuse popped so I'm hoping that saved everything else. But the questions is, what the hell is my problem?? All the diagrams I've seen online seem to match that way I've wired this, so I'm a bit stumped. Fwiw, this time the fuse blew the jeep was running, however the previous time it was sitting off with only the accessories on.

I drew a quick diagram of exactly how I have it wired.

And here is the relay. Well, the top one (the bottom is for my HEI distributer).

Binder · Apr 14, 2009

How many amps do the lights draw each? Are you sure you don't have the lights wired is series? How long is the circuit between the fuse to the lights?
BTW you really shouldn't wire a buch of stuff into your battery, it isn't your power source. The alternator is.....That isn't the issue here though.

Nuzzy · Apr 14, 2009

Binder said:
How many amps do the lights draw each?

I'm not sure on the amps, but they are stock replacement Sylvania "XtraVision" lights. I have them wired to the high beams only, and although I couldn't find amperage draw on their website and their call center was closed, their site does say 65 watts as opposed to 55 for low beams.

Binder said:
Are you sure you don't have the lights wired is series?

No, I'm not sure of this, and that could certainly cause a problem! I tried to match the way I originally saw the lights wired. The power wire went seemingly went into the passenger side plug and then back out the same part of the connector over to the driver. As it sits now, I ran a length of wire from high power out on relay towards the passenger light. Then another length from driver over to passenger light. I took both those ends meeting at the pass light and twisted them together/soldered into a female spade to attach to the high beam prong coming out the back of the light.

Binder said:
How long is the circuit between the fuse to the lights?

Power junction block to fuse is 12-14 inches --> fuse to relay is 6 inches --> relay out to passenger light is length of hood from firewall --> length of wire from pass to driver light is length of grill.

Binder said:
BTW you really shouldn't wire a buch of stuff into your battery, it isn't your power source. The alternator is.....That isn't the issue here though.

True, although technically I only have one wire actually coming off my battery which is located in cab. Battery power runs to a junction block on firewall as does alternator and all power is disseminated from there.

nevada · Apr 14, 2009

um...how is a 30 amp fuse, going to work with a 30 amp relay?

on my bike when i wired up the lights for duals...i used a 30 amp relay, and a 15 amp fuse. they cant be the same, or you run the risk of burning things up again.

how about a 50 amp relay, and a 35 amp fuse?
sounds like your just drawing too many amps. have you tried it with only 1 light plugged in?

Nuzzy · Apr 14, 2009

nevada said:
um...how is a 30 amp fuse, going to work with a 30 amp relay? on my bike when i wired up the lights for duals...i used a 30 amp relay, and a 15 amp fuse. they cant be the same, or you run the risk of burning things up again.

Good question. I suppose I could put a 20 or 25 amp fuse...

nevada said:
how about a 50 amp relay, and a 35 amp fuse?
sounds like your just drawing too many amps. have you tried it with only 1 light plugged in?

Haven't tried it with one light. Prolly a good test.

I just can't imagine that stock headlights would require more than a standard 30 amp relay which claims to be "made for headlights"... :eeek: I'm fully prepared to admit if I'm way off base, but that just seems weird.

Nuzzy · Apr 14, 2009

So I just checked the Sylvania site again. The design watts for the high beams are 65 and the design volts are 12.8. By my math, and the equation watts = amps x volts, I get that 2 x 65 /12.8 = about 10 amps between the two lights.

What the hell could be causing so much extra power to be drawing through the headlight relay... And fwiw, so far all the other wiring is holding strong without popping fuses.

Not Jobless · Apr 14, 2009

Remove relay and check the wiring to ground with an ohm meter, you may have a short.

Replace the relay

One other thing, those relays are not sealed, if mounted on their side or upside down you stand a better chance of getting water in from where the electrical connections are.

Fordzuki · Apr 14, 2009

IIRC, that's exactly how I have the lights wired on the LJ, except I also threw the taillights into the mix on the same relay. But if I remember right, I've got a 15 amp fuse, and a 30 amp relay, with a simple toggle on the dash.
When I get home tonight, I'll see if I can't trace it down and confirm this.

Nuzzy · Apr 14, 2009

Jackazz said:
Remove relay and check the wiring to ground with an ohm meter, you may have a short.

Check the headlight grounds or the relay ground...? Never used an ohm meter (I know, I'm a :looser

so what/where would I be looking for readings wise to test for a short?

Not Jobless · Apr 14, 2009

Nuzzy said:
Check the headlight grounds or the relay ground...? Never used an ohm meter (I know, I'm a :looser so what/where would I be looking for readings wise to test for a short?

You want to look for shorts in the wiring...a nick or cut that could be contacting the chassis or body.

After looking at the build thread and seeing that they work for 10 minutes before blowing the fuse I'm thinking the relays are ****.

Replace the relay and try again.

Lamar · Apr 14, 2009

Dear Nuzzy;
OK my friend, your wiring schematic is correct. Assuming that the wiring is exactly as per your drawing, I'd say that you have a short to ground somewhere between terminal #87 and the headlights. The reason why I state this is because the headlights are operational for a short period of time before something in the circuit caused both the headlamp and the relay to fry themselves.

Also, 30 amp fuses are not reccomended as 30 amperes of power can melt the wiring before the fuse will blow. A 20 amp fuse should be more than adaquate for your requirements, my friend.
Your friend;
LAMAR

Boosted · Apr 14, 2009

Nuzzy said:
Check the headlight grounds or the relay ground...? Never used an ohm meter (I know, I'm a :looser so what/where would I be looking for readings wise to test for a short?

You are just looking for continuity. Easiest way is set the multimeter to audible (alarm) and touch the two probes together....you will hear a "beeeeeep". Now, this is a very generic but easy way to do a basic short test. Attach one probe to one end of the wire you are testing and the other probe to a ground. If it beeps, you got a short. Next step would be to trace the wire and find the short. :;

64FJ40 · Apr 14, 2009

Did the bulb(s) blow this time?

The only scenario I can think of that blows the bulb is if you have the bulbs wired in series with no ground at the first one. But then I think you would notice that the bulbs are dimmer than they ought to be since you'd be running them on 7-ish volts. At 7 volts, they'd be drawing 20+ amps, which will either fry the first bulb's element or cook the connector and make it wisp smoke as it burns.

Verify your wiring diagram and make SURE there is a good ground at the correct terminal of each plug connector.

Nuzzy · Apr 14, 2009

I circumvented the relay and confirmed both headlights do still work. Then I replaced the blown 30A with a 20A fuse.

I set my tester to the ohms setting and according to it's manual was looking for it to change from 1. to 0.0 when touching tips, which it did. I then tested the ground screw of each headlights' ground wire against the motor and frame and all measurements came out to to the 0.0. I did the same to the ground screw for the relay and also got 0.0.

I then tried to measure the amp draw by placing the red lead onto the high beam spade of the pass light and the black against my block ground. I was expecting close to 10 amps (12.6 volts at the time) but the meter immediately shot up to 16-17amps and then promptly fried itself

So, now I'm off to grab another multi meter and another relay or two. Also, all wires look in good working order without any obvious ground issues

So if it's ground, it's hidden...

Binder · Apr 14, 2009

I wonder if you may be getting power spikes in the system? A short circuit should not have burned out the light bulb but wired is series would have or a spike along with too large of a fuse......Have you had issues with other electrical components?

Binder · Apr 14, 2009

Nuzzy said:
I set my tester to the ohms setting and according to it's manual was looking for it to change from 1. to 0.0 when touching tips, which it did. I then tested the ground screw of each headlights' ground wire against the motor and frame and all measurements came out to to the 0.0. I did the same to the ground screw for the relay and also got 0.0....

You should do this same test with the hot wire to the lights. Just unplug both lights and test between the power wire at the lights and the frame (lights turned off). If you have other than a reading of 1 try again with the same wire unplugged at the relay. If you still have other than 1 there is a short in the wire. If there's resistance with the first test but not the second the relay is probably bad.
Make sense? I hope I wrote that out right.:haha:

Not Jobless · Apr 14, 2009

Have you replaced the relay yet?

Nuzzy · Apr 14, 2009

Well, I think I may have a likely culprit...

I grabbed a handful of new relays figuring spares wouldn't be a bad thing, and put one of them in. However, then I got to looking more closely at the back of the lights themselves through the access cutouts in the backside of the grill and noticed something. It appeared the light prongs might be closer to my radiator than I'd anticipated. I flexed the grill and sure enough, contact.

To fit my elec fan I had to move the rad forward in the grill a few inches. This caused an interference with the back of my light cups which I then modified. I thought there was enough clearance, but now I'm pretty sure that's not the case.

The solder on the exposed plug was just close enough to the rad to make contact under certain conditions.

Stuck elec tape over the solder, put heat shrink over the connector, and used 1/4" thick nuts to space the whole light forward a bit.

Did the same to the other side and then left the lights on for 15 minutes without issue. This would make sense since the lights hadn't popped last night until I hopped in and put the jeep in gear and started moving. My guess is that movement flexed the grill just enough so that the powered prong made contact and shorted the whole deal.

I suppose time will tell, but I'm hoping this was it.