Quick ? about the H4 headlight upgrade - ground circuit.

[garyfish340]

When converting to a basic H4 headlight, is it okay to run a separate ground wire for those head lights ? Originally, I think Chrysler had the drivers side marker pigtailed to the left headlight, pigtailed to the left parking light, than to the right side in reverse order, with a black ground wire travelling back to radiator support, in front of the battery. Can I run the same circuit minus the headlights, and than back to the negative battery ground, and a second stand alone headlight circuit with a bigger ground wire running to the negative battery ? I'm running 14 gauge for the new headlights, and it's easier to unplug the headlights, strip, tin, and solder the blacks, rather than to create a whole new ground circuit, and soldering in side markers, and parking lights. I need the upgrade in headlights to see better at night here in the mountains, not for the cool modern factory. Thanks

 

[C130 Chief]

The ground should be the same gauge or larger than the supply wires. So if you build a headlight harness with 14 AWG wires all three wires for each lamp should be that size. The ground should be as short as possible connected directly to the body.

Keep the factory wiring as-is for the markers and make you supplemental headlight harness. Pigtail the ground to a headlight bucket screw.

 

[gen2hemi]

If you are using H4s pls confirm you are using a relay harness too - ie your headlight or high beam circuit (red & purple) is only sending +12v to energize a relay that is supplying the current to the bulbs? Do not use your stock headlight and dimmer switch to power H4 bulbs - period. In these H4 harnesses, whether you buy it or make it (plenty of diagrams online) the dedicated ground for each bulb is run in the harness and generally routed out and ganged to a terminal ring that you put under the bolt on the core support where the rest of the forward grounds go. The hot lead for the relays is usually paired to the starter solenoid always hot stud. Makes for a clean harness install and you know both hot and ground are sized for the H4 load (prefer 12ga but 14ga is adequate).

 

[crackedback]

I build relay harnesses for headlights. I use the original headlight circuits to fire each relay. Some feel the original wiring is good and acceptable. I think it's undersized garbage, plenty of voltage drop and provides poor performance. Ask any of the people that have installed a kit whether the original stuff is good.

If you are putting new headlight sockets in, I would not use any of the original ground circuit. Make a fresh set and ground them to the yoke or back to the point where your secondary ground line runs from battery to yoke. The grounds tend to link in series in an original harness. Continue to run that ground circuit for your markers/turns/etc and run dedicated grounds for your headlights. No harm in pulling the grounds for your headlights out of the system as long as the ground lines running into the original headlight sockets remain unaltered.

 

[garyfish340]

If you are using H4s pls confirm you are using a relay harness too - ie your headlight or high beam circuit (red & purple) is only sending +12v to energize a relay that is supplying the current to the bulbs? Do not use your stock headlight and dimmer switch to power H4 bulbs - period. In these H4 harnesses, whether you buy it or make it (plenty of diagrams online) the dedicated ground for each bulb is run in the harness and generally routed out and ganged to a terminal ring that you put under the bolt on the core support where the rest of the forward grounds go. The hot lead for the relays is usually paired to the starter solenoid always hot stud. Makes for a clean harness install and you know both hot and ground are sized for the H4 load (prefer 12ga but 14ga is adequate).

Originally: before there were any modifications to any wiring. I ran a 4 gauge wire with a giant fuse, from the 138 amp alternator, to the starter relay. This is because I needed the car to function, while move it around during the build process, and it's my opinion, a amp-meter might be okay for a 38 amp alternator, but not a 138 amp unit. Plus the wiring harness to the instrument panel is probably stiff as hell. Since electrical was the last process in the build. First I ran two 10 gauge fused/circuit breaker ( have no Idea what amps yet) wires to two 30 amp relays. Next I ran the purple, and red wires, one to each relays. Than ( because of availability I ran a blue ( cold ) 14 gauge wire from the low beam - relay to the drives side headlamp, than to the passengers side. On relay be I did the same with the red ( hot= high beam ) 14 guage. Than I ran a black 10 guage from the drivers side HL to the passenger side HL, and than back to the rad support by the other grounds. The side marker had a ground that went directly to the rad support already. ( Before I touched anything the drivers side HL, pigtailed it's ground off to the passenger side HL, and than the side marker.) So on the passenger side HL plug pigtail, I soldered the two black together. So that ground now runs like this - Drivers side marker, to passenger side marker, and back to the common rad support ground. Last time I did this harness, I didn't replace the headlight switch, or dimmer with anything more than a stock NAPA replacement. Only because the old switches looked like they had 45 years of nasty all over them. That system, with it's cheap plastic/glass h4 housings lasted 7 years. Whether it was good luck I had no bad luck, I can't say. This car is getting overkilled on everything. So now you have a complete back ground, and story, thanks guys, and have at it.