Anybody know what the amperage draw on the headlights is?

[ThisGuyUKnow]

Like the title says, I need to know what size fuse I need and also what gauge of wire I need to use if I want to relay my headlamps. I'm thinking of making a relay/fuse distribution center for my fi project and I might as well relay the lights if I do.

 

[Peanut Butter]

Take the watts of the headlight and devide by the power which is 12 volts and your answer is the amps used. For the most part headlights are 35 watts low beam and 55 watts high beam. So that's 2.92 or 3 amps for low beams and 4.58 or 5 amps for high beams. Not as much as you might think. Where this really factors in is aux. lights that are 100 watts or more. I would recomend 10 ga wire for the power in and out based on the amount of time the lights are on and the length of the run. That's over kill, but good insurance. Rod

 

[ThisGuyUKnow]

Take the watts of the headlight and devide by the power which is 12 volts and your answer is the amps used. For the most part headlights are 35 watts low beam and 55 watts high beam. So that's 2.92 or 3 amps for low beams and 4.58 or 5 amps for high beams. Not as much as you might think. Where this really factors in is aux. lights that are 100 watts or more. I would recomend 10 ga wire for the power in and out based on the amount of time the lights are on and the length of the run. That's over kill, but good insurance. Rod

Word! 10 gauge actually might not be overkill, I am going to be running the relays from the passenger fender.

 

[IOPort51]

Digital Multimeter - Save on this AC/DC Digital Multimeter

This is my favorite cheep meter, will do DC amp measurement easily up to 20 amps.

I think the high beams are 6 amps but I will check again, I have slept a few times. 14 gage wire is good for head lights.

The FI needs a relay for the fuel pump that is triggered by the oil pressure switch.

 

[ThisGuyUKnow]

Digital Multimeter - Save on this AC/DC Digital Multimeter

This is my favorite cheep meter, will do DC amp measurement easily up to 20 amps.

I think the high beams are 6 amps but I will check again, I have slept a few times. 14 gage wire is good for head lights.

The FI needs a relay for the fuel pump that is triggered by the oil pressure switch.

Thanks, I already have a multi meter. I just am surprised the highbeams pull under 10 amps, i think all the headlamp relay kits i have seen have really heavy wiring. Arent the upgraded lights you can buy at quadratec still only like 55watts?

Im looking at the charts and it looks like even running from the pdc on the pass fender to the driver's side light harness 14 gauge would be overkill. if all it has to carry max is 6 amps. Ill probably go with 14 gauge and a 10 or 15 amp fuse.

Not sure why you mentioned the the FI relay but yeah I understand that it is wired to the oil pressure switch.

 

[PaRenegade]

I plan on using 12ga. for my headlight relay circuit. Even that is a bit overkill, but I have the wire. Distance also plays a part when figuring wire size and these are short distances. I'm sure 14ga. would be fine at this distance. Heck the factory was 16ga. and that was a longer run. But we know that was pushing it and also the reason we upgrade to begin with. I think most upgrade harnesses use 12ga. I believe Jimbo was building these for sale a while back. Do a search for headlight harness.

edit: Here's the link to the thread.
http://www.jeep-cj.com/forums/f7/an...-pre-made-head-light-upgrade-harnesses-19110/

 

[cj7inthetwigs]

12 gauge is rated for 20 amps. I would use that too specially when I have rolls of it laying around. Voltage drop shouldn't matter on vehicles . On the job , we dont worry about voltage drop until well over 100' and even then at that distance it not going to make a difference. IMO, 14 gauge should be fine but I would not hesitate on using 12 or even 10 if it was free. I might freak out if someone ran some 500kcm though

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[IOPort51]

Thanks, I already have a multi meter. I just am surprised the highbeams pull under 10 amps, i think all the headlamp relay kits i have seen have really heavy wiring. Arent the upgraded lights you can buy at quadratec still only like 55watts?

Im looking at the charts and it looks like even running from the pdc on the pass fender to the driver's side light harness 14 gauge would be overkill. if all it has to carry max is 6 amps. Ill probably go with 14 gauge and a 10 or 15 amp fuse.

Not sure why you mentioned the the FI relay but yeah I understand that it is wired to the oil pressure switch.

"I'm thinking of making a relay/fuse distribution center for my fi project and I might as well relay the lights if I do." I was thinking the lights were just an after thought.

I have 3 or 4 meters but this is the only one that will measure up to 20 amps DC.

 

[ThisGuyUKnow]

"I'm thinking of making a relay/fuse distribution center for my fi project and I might as well relay the lights if I do." I was thinking the lights were just an after thought.

I have 3 or 4 meters but this is the only one that will measure up to 20 amps DC.

What fi setup are you doing.... I'm going to use a pd c from a 4.0 and integrate it into my too harness... the vette donor didn't have a true pd c. Going to eliminate the solenoid and run the alt and starter through the pd c. It's going to be very clean when I'm done.

 

[cj7inthetwigs]

Have yall considered buying a clamp meter? You won't have to worry about that 10 amp fuse anymore when reading current . Fluke meters are costly but consider what it is and go ahead and spend the money. I like Northern Tool and Harbour Freight ,but a meter is something I put my life in when at work. I know, I know we are measuring headlight current here and not a 1200 amp piece of switch gear.

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[ThisGuyUKnow]

http://www.crcorp.com/DCT_HardwareEssentials/E/pdf/E11.pdf

according to the above chart 10 amps can be handled by a 16 gauge wire up to 20 feet. If that is correct then I should have nothing to worry about. I have been seeing different charts with different figures

 

[IOPort51]

Just put the amp meter on the lights. The low beam draw 7 amps DC and the high beams draw 10.

My reference states that 14Ga will handle 40 amps DC, 16ga -20ADC and 18ga -10ADC.

The one thing I do not like about that cheep HF meter is it does not turn itself off.

Had to hunt up a fresh 9v.

 

[IOPort51]

I think I like 14 ga because the 14-16ga crimp fittings fit better than on 16ga wire.

 

[ThisGuyUKnow]

Just put the amp meter on the lights. The low beam draw 7 amps DC and the high beams draw 10.

My reference states that 14Ga will handle 40 amps DC, 16ga -20ADC and 18ga -10ADC.

The one thing I do not like about that cheep HF meter is it does not turn itself off.

Had to hunt up a fresh 9v.

At how many ft? I just looked at the original cherokee fuse center and they put a 40 amp fuse on the headlamps, with your reading that seems to be 4 times the need for the lights wonder why they have such a large fuse

 

[Jimbos76cj]

When i build the harnesses I use 12 ga wires for the relays to harness and solenoid or battery to the relay. I set em up with 10 amp fuses low and 15 high. Most headlights are 55 watt low and 65 high.. at 12 volts thats just over 9 amps low and 11 high. I would also run your ground wires back to the motor ground or battery ground. please dont use 16 ga wire.

 

[IOPort51]

At how many ft? I just looked at the original cherokee fuse center and they put a 40 amp fuse on the headlamps, with your reading that seems to be 4 times the need for the lights wonder why they have such a large fuse

The fuze center you are using is from an XJ?? Different kind of headlight, maybe? I would have to look at a diagram to see if there was anything else on the light circuit.

Distance is kind of academic when you are just going from one side of the engine compartment to the other. Even if it were 20 amps at 10 feet or 20 amps at optimum conditions it still is valid.

 

[ThisGuyUKnow]

When i build the harnesses I use 12 ga wires for the relays to harness and solenoid or battery to the relay. I set em up with 10 amp fuses low and 15 high. Most headlights are 55 watt low and 65 high.. at 12 volts thats just over 9 amps low and 11 high. I would also run your ground wires back to the motor ground or battery ground. please dont use 16 ga wire.

What is the gauge of the factory headlamp wires?

I knew your kit is relay nice cause I've considered buying one but 12 gauge is incredible over kill for a 12 amp less circuit. Ill probably with 14 ga in mine. You shouldn't need two fuses for it either the same fuse can supply power pin 30 on relay for both and low beams.

Why run your ground back to the negative on the battery or motor? Ground is ground the world around, do long as you are grounding the lights to the body of the grill and there is a clean connection with no resistance ie the ground loose, dirty between wire the chassis, or paint , etc. It is the same as grinding to the block our the bat there is no need to run an extra wire all the way back to the bat.

 

[Jimbos76cj]

What is the gauge of the factory headlamp wires?

I knew your kit is relay nice cause I've considered buying one but 12 gauge is incredible over kill for a 12 amp less circuit. Ill probably with 14 ga in mine. You shouldn't need two fuses for it either the same fuse can supply power pin 30 on relay for both and low beams.

Why run your ground back to the negative on the battery or motor? Ground is ground the world around, do long as you are grounding the lights to the body of the grill and there is a clean connection with no resistance ie the ground loose, dirty between wire the chassis, or paint , etc. It is the same as grinding to the block our the bat there is no need to run an extra wire all the way back to the bat.

Every thing I read said to go min 14 ga.. so i use 12. The factory Ive found has been between 16-20 ga

your correct you can power the high and lows from one relay but that means that your power is coming from the stock head light switch. The whole point behind adding the relays is to get away from the head light switch and get your power directly from the battery.

If you check the power going to your light sockets in stock form you should be around 11 ish volts. Your alt should be putting out around 14-14.6 volts. your loosing 3 volts in the wiring between the battery and the sockets. If your gonna keep the power going through the stock switch to the relay you might as well just leave it stock.

Remember that the 87a leg of the relay is normally closed so if you have 12 volts going to it all the time what ever is hooked to that leg will be on. unless your using a dpdt relay


As for the ground going to the battery or motor the first 2 harnesses I built for local guys had poor results grounding to the grill. It was greatly improved by moving it to the battery. I even had one that the ground was so bad to the fender that the relay wouldn't work. Thats why I started adding the relay into the ground circuit going to the battery or motor.

Trust me I tried to figure out how to make it work with one relay but have come up empty.. If you have a way please share a schematic.

 

[IOPort51]

I have copper blocks at different locations that are all 10ga wired back to the neg. terminal of the battery. In a perfect world a ground is a ground, in a CJ a ground can be an illusive thing.

 

[ThisGuyUKnow]

Every thing I read said to go min 14 ga.. so i use 12. The factory Ive found has been between 16-20 ga

your correct you can power the high and lows from one relay but that means that your power is coming from the stock head light switch. The whole point behind adding the relays is to get away from the head light switch and get your power directly from the battery.

If you check the power going to your light sockets in stock form you should be around 11 ish volts. Your alt should be putting out around 14-14.6 volts. your loosing 3 volts in the wiring between the battery and the sockets. If your gonna keep the power going through the stock switch to the relay you might as well just leave it stock.

Remember that the 87a leg of the relay is normally closed so if you have 12 volts going to it all the time what ever is hooked to that leg will be on. unless your using a dpdt relay


As for the ground going to the battery or motor the first 2 harnesses I built for local guys had poor results grounding to the grill. It was greatly improved by moving it to the battery. I even had one that the ground was so bad to the fender that the relay wouldn't work. Thats why I started adding the relay into the ground circuit going to the battery or motor.

Trust me I tried to figure out how to make it work with one relay but have come up empty.. If you have a way please share a schematic.

I think you misunderstood what I was saying , I didnt mean one rly i ment you shouldnt need 2 fusese. You only need one fuse in the CKT before pin 30 on both relays if they are wire like the attached link. You want to keep ckts as simple as possible.

Using 12ga wire is fine but my point was it was unnecessary to handle the current. By all means keep using it in your manufactured kits they are clean and look great.

I generally like to build ckts one step higher than what they need. Everything I am seeing is showing that at those lengths the bare minimum I can get away with is 16 ga for those amps. So when i build mine I will go with 14 gaugean probably 1 15a fuse between the bat and pin 30 on both relays.

87a would not be used at all.

I was not saying that any pwr for the lamps would go through the dash switch.


Ive never had problems with getting a decent ground at the grill or fender, If that is the case then yes it makes sense to send the ground to the bat or the engine, but if that is the case then you need to seriously look into why you have no ground on your fenders or grills because you have some serious issues, like maybe your fender isnt bolted to your frame or something

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