current draw /wire size question

[VIRGIN MIKE]

I am reworking the front harness and need to know the max current draw of the headlights to determine proper wire size - 5 wires is a tight fit at the choke point - or I think I could tie ground directly to the housing and only need 4 wires. Any thoughts?

[narly1]

When in doubt hook them up to a battery or other 12V source with a current shunt in series.

See https://en.wikipedia.org/wiki/Current_sensing the part about shunt resistors.

These shunt resistors are cheap and extend the current measuring range of your typical multimeter without the risk of damage due to putting too much current through it. Most are only rated at a few amperes.

[NAZ]

If you have 55 watt halogen bulbs, each would draw 4.6A at 12 VDC. That's if you are running separate high and low beams, if you like to run your low beam with your high beam you need to add the total wattage and divide it by 12 (12-volts) to get the current.

[edwardb]

You're using the truck kit supplied LED headlights? Like all LED's, they will draw much less than halogens which the RF harness can be used for. Personally, I would use the same size wires as in the harness though. Easy enough to measure the amperage though with a VOM or amp gauge. Don't know that I would personally trust the headlight housing as a ground. But again easy enough to measure if you really need to go that way. Obviously depends on if you're doing a fender mount (no go) or mounted on the radiator/shroud area.

[VIRGIN MIKE]

Thanks, I'm using the LEDs supplied with the Kit (no specs to be found)

[edwardb]

Thanks, I'm using the LEDs supplied with the Kit (no specs to be found)

I dug out the headlights Factory Five supplied with my truck kit and measured them using a regulated power supply and digital clamp meter. As suspected, their current draw is quite low:

Low beam headlight = 1.3 amps
High beam headlight = 2.5 amps
Parking light = .3 amps
DRL = .3 amps

That's of course for one fixture. Actually running would be times two. Stand by my original advice. The standard Ron Francis wire and gauges is more than up to the task since it will handle the kit provided halogens and incandescent bulbs. But I'd still stick with the same gauge wire. BTW, just for comparison, the kit supplied halogen bulbs won't light with my regulated power supply. It's rated for 13 amps and goes into overload when I've tried to light them. So clearly they're more than 13 amps. Pretty crazy when compared to what the LED's do.

[VIRGIN MIKE]

Thanks edwardb, 2.5 amps for high beams is the critical number I needed; looks like 18 gage will be safe for length of runs where I plan on using it; staying with the supplied Ron Francis Harness for the most part. I want to move the +12 bus from the starter, and add an accessory +12 buss, battery switch, and accessible charging posts. At 5'8" I was able to elevate and tilt the seat a bit, creating room to relocate or add an an aux. battery behind the seat

[Pat Landymore]

Mike:
You’re on the right track! I used 16 Ga for my ground, 18 for Hi and Lo beam, and 20 for Park/Signal (yellow light) and the DRL’s. It all slid very easily through that narrow mounting bolt.

Humbly suggest you check the schematic diagram for the harness that comes with the kit...I couldn’t find a fuse for the actual headlight circuit (note there are two feeds...Headlight SW 1 and 2) and added one to Headlight SW 2. Did similarly to what you said and split up the wiring to add a junction block for the different gadgets in my truck. It worked well.

Pat

[edwardb]

...I couldn’t find a fuse for the actual headlight circuit...

Right. The RF panel has fuses for the brake lights, parking lights, hazards and turn signals. But not the headlight feed. The kit provided AC-Delco style headlight switch however does have an internal resettable circuit breaker for the headlights. So the headlight feed is protected if you use it. The risk though IMO is if you add smaller gauge hook-up wire to the circuit it could fail before the breaker trips. That's one of the reasons I responded how I did. Adding in-line breakers or fuses is another option, as mentioned.

[Pat Landymore]

Hi Edward:

Did I miss a reference in the wiring manual or the FFR manual to a circuit breaker in the headlight switch?
If so that would be really embarrassing🙈

As for the wires sizes I said I used, fully understand your precautionary approach.

For my build, only used them for about a foot of length to (tidily) get through the headlight mounting bolt without crowding the wires, then connected to the supplied FFR/Ron Francis harness as delivered.
Apologies if I’ve confused or misled anyone.

Cheers,
Pat

[edwardb]

Hi Edward:

Did I miss a reference in the wiring manual or the FFR manual to a circuit breaker in the headlight switch?
If so that would be really embarrassing��

As for the wires sizes I said I used, fully understand your precautionary approach.

For my build, only used them for about a foot of length to (tidily) get through the headlight mounting bolt without crowding the wires, then connected to the supplied FFR/Ron Francis harness as delivered.
Apologies if I’ve confused or misled anyone.

Cheers,
Pat

No, the existence of the circuit breaker isn't documented anywhere in the Ron Francis wiring book or the Factory Five instructions that I've seen. But it's been talked about a bunch in the past and guys have posted schematics. I just did a quick search and couldn't find a copy to post. So I guess you have to trust me. :rolleyes: It's a 30 amp resettable breaker. It's a ACDelco D1588 equivalent if you want to search. Ron Francis, Painless, American Autowire, and probably lots of others sell the same compatible switch. It's talked about in some of their documentation. But no schematic.

[VIRGIN MIKE]

Thanks for the good info, guys I agree with all of it - Here's where I'm at - got everything put together; now going back to correct a couple of small details. The day I lost my build space and drove home, not happy, changing the TO to hydraulic, possibly tidy up the wires and finish the firewall141501141502141503

[VIRGIN MIKE]

Wow a 30 Amp breaker - The wire would melt first wouldn't it?