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Automotive wire vs. regular wire

montanaman

NAXJA Forum User
Location
Western Montana
Hey ... I'm getting ready to make a 10-gauge headlight wiring harness via the instructions on GoJeep's website. GoJeep says "Make sure you use automotive or marine wiring."

Home depot has 10-gauge multi-strand wire by the foot, but it's not listed as "Automotive."

What's the difference? I can't see anything about the factory wires in my jeep that look any different from the stuff in Home Depot.
 
house wire doesn't have the flexibility that auto does, the strands are larger and prone to breakage due to vibration. also a difference in the housing material.

that's not to say it doesn't work. I did my MG from bumper to bumper with THHN and put 20000 miles on it without a failure. Just make sure the stuff you pick up says THHN on the roll. It's gasoline and petroleum resistant.
 
The insulation is somewhat more resistant to chemicals and abrasion - while houshold wiring is typically designed for more benign environments.

However, the "industrial" (black rubber jacket) extension cord works well for lighting - as long as you keep it away from heat and such. Black rubber 10/3 works well - that's what I used to make my headlamp harness (with 18/3 for the "trigger" leads to the relay box up by the football.)

If you're going to upgrade your headlamp wiring, then relays are vital - the OEMR headlamp switch is just barely able to handle the current from 55/65W bulbs for long-term - they usually end up burning out. Taking that load off the switch will help with switch longevity - and it will help with lamp output anyhow (shorter power circuit.)

5-90
 
5-90 said:
If you're going to upgrade your headlamp wiring, then relays are vital

Yeah ... absolutely. I found the relays at a great price at partsexpress.com.

I'm probably going to upgrade to the 55W headlamps. They are cheap and should provide all the light I need when combined with the new harness.

I'm also thinking I'll just cut into the original wiring and route the factory headlight power directly to the relays, rather than running a wire from the factory plug all the way up to the relay.
 
What I did -

Plug into the OEMR headlamp harness for relay "trigger" signals
Provide main lamp power from the battery (OK, from a distribution post I've got directly connected to the battery...)
Bought Hella E-code housings and 90/130W H4 bulbs

Aimed carefully - the sharper cutoff of the low beams can be misdirecting. I think they're aimed just a touch HIGHER than they were before - but I don't remember (it's been a few years.) However, I have yet to be "flashed in annoyance" by anyone going the other way with my low beams on, so I must have done something right. Even cops don't seem to care - and I've been asked about them before.

Good job on Parts Express - I'd probalby have sent you there anyhow. They carry Bosch relays for about $3 each - and I've got to stock up... I can get them for about $8 locally.

5-90
 
montanaman said:
Yeah ... absolutely. I found the relays at a great price at partsexpress.com.

I'm probably going to upgrade to the 55W headlamps. They are cheap and should provide all the light I need when combined with the new harness.

I'm also thinking I'll just cut into the original wiring and route the factory headlight power directly to the relays, rather than running a wire from the factory plug all the way up to the relay.

Don't cut into anything, use the sockets that the stock headlights used, get 3 spade connectors, use the old headlight power to trigger the relays. Then you can use the other socket to do the same thing if you happen to decide to put any aux lights on like driving lights, that way you can use the other high beam to trigger a driving light relay [with a switch in between of course] and the low beam other one to power say a set of rock lights underneath, again with a switch so you can turn them on and off when not needed.
 
montanaman said:
Hey ... I'm getting ready to make a 10-gauge headlight wiring harness via the instructions on GoJeep's website. GoJeep says "Make sure you use automotive or marine wiring."

Home depot has 10-gauge multi-strand wire by the foot, but it's not listed as "Automotive."

What's the difference? I can't see anything about the factory wires in my jeep that look any different from the stuff in Home Depot.

GoJeep might be referring to stranded wire that has each individual strand "tinned". This has has better protection against corrosion caused by the elements. It's for sure more expensive.
 
If you use wire from HomeDepot,

Stranded wire listed for structured wiring will be fine for automotive use. However, use MTW/THWN. MTW is machine tool wire which is flame retardant, moisture and oil resistant with a thermoplastic insulation, and THWN is similar, but with a nylon cover over the thermoplastic. Both are designed to be used at a maximum operating tempurature of 194°F. THHN is not impervious to moisture, therefore it should be avoided unless the jacket's label is accompanied by the previous designations.
 
Many Hardware Stores and Home Building Supply Stores usually sell "Hook-Up" wire. Its designed for use in repairing appliances and not Home in wall electric supply. I would "THINK" Hook-Up Wire is vibration and chemical resistant, since that is the environment in appliances.

Is it the equavelant to Automotive Wire?? I don't know, and would search for a description of what the insulation is constructed of, unfortantely, I've rarely found a description of the insulation material for the Hook-Up Wire they sell in hardware stores. If I find anything, it just says plain old PCV.

I have used generic Hook-Up wire from the Hardware Store for low load circuits in vehicles several times before and never had a problem with it. The only problem I have had, was my own fault for not routing and securing the wire properly and it was mechanically damaged, i.e. cut/chaffed. I found routing the wire within existing harness's or taping it directly over the existing harness works best (if it must make a run all on its lonesome, at least cover it with the convoluted tubing and tie-tie it to secure points along its route. These circuits were low load, like Autometer Gauges and Stereo's, not 20 amp headlight circuits. It might be best to do as suggested and put in the extra effort to find Specific Automotive Wire.

Also, Don't forget Circuit Protection, there should be a fuse or circuit breaker in your circuit, that includes using a relay, there needs to be circuit protection on both sides of the relay. You don't want your custom headlights setting your whole jeep on fire, do you? It does happen and is more common than people think.

Also, soldering connectors and shrink wrapping the ends does wonders for reliability. I know that many OEM harness's are NOT soldered or shrink wrapped, BUT they are crimped by machine and/or hi-quality tools, something you NOT doing, so make up for it by soldering the connections and shrink wrapping them.
 
Soldering isn't used OEM due to time factors for assembly, and because it actually is more brittle than a crimped connector. It leads to failures during durability testing, specifically during the vibration cycles.

In general, design temps for the vehicle are:

General Passenger Cabin: 85 C (185 F)
Cabin Headliner and other ares with direct sun contact: 105 C (221 F)
Underhood: 125 C (257 F)

At least, those are numbers for Chrysler. Other OEMs(especially Japanese) sometimes have some variations, although underhood is generally 125 for everyone.


Generally, you are worried about:

Jacket heat resistance
Jacket material resistance (such as oils, solvents, etc)
Number of strands.

All in all, its not really common for people have failures of the wire itself, except for melting wires on something hot like the exhaust manifold.

Sticking with a nice stranded good size wire, you should be fine with the jacket types above.

14 gage for 15 amp
12 gage for 20 amp
10 gage for 30 amp

You can get away with a lot more current in specific situations, but those are nice safe numbers. When we are determining our harness sizes for the vehicle in general, we are considering the max current draw under worst base conditions, fuse size, length of run, and how the wire is bundled (capacity cahnged based on whether its indivitual or buried in a larger harness, due to thermal considerations).

Generally, OEM wire sizes are way to small for my taste. But, being on the 'inside', I understand all the considerations into harness design, so I know why they do what they do, even if I don't like it..
 
If you solder the connections use shrink wrap about 1 1/2 times the length of the solder joint. This will help support the joint. Solder joints are kinda brittle and could snap at the end of the solder.

Sarge
 
5-90 said:
The insulation is somewhat more resistant to chemicals and abrasion - while houshold wiring is typically designed for more benign environments.

However, the "industrial" (black rubber jacket) extension cord works well for lighting - as long as you keep it away from heat and such. Black rubber 10/3 works well - that's what I used to make my headlamp harness (with 18/3 for the "trigger" leads to the relay box up by the football.)

If you're going to upgrade your headlamp wiring, then relays are vital - the OEMR headlamp switch is just barely able to handle the current from 55/65W bulbs for long-term - they usually end up burning out. Taking that load off the switch will help with switch longevity - and it will help with lamp output anyhow (shorter power circuit.)

5-90
Rubber covered cord with the prefix JA JS is oil resistant.
 
just go to advance and buy the wire and relays, simple and cheap enough and intended for the environment you're going to put them in

you should be putting loom around the wires anyway, so the insulation won't really matter as much as you're making it out to..........especially where these wires run, the only thing possibly bad for the wires that they run by would be the battery. If you've got a leaking battery you've got bigger problems than headlight wiring.........
 
I've never had a soldered joint snap, but I agree that they are more brittle, and could see how the vibration testing for the OEM would lead to thier decision.

The OEM's also have the time and resources to find the proper connectors and tools to make a perfect crimped connection. We on the other hand, don't have those resources.

I've had plenty of crimped connections come apart, corrode or break because of either the quality of the connector (the only one I could find that fit the application) or the compatibility of the connector with the less than proffesional crimping tools I have.

I'd suggest you test any crimped connection you make yourself, make sure it will hold, if your in doubt, I'd solder it and shrink wrap it.
 
One of the best crimping tools I've run across is the "Electrician's Staking Tool" by Gardner-Bender. Find it at hardware stores.

It seems to work quite well with nearly any crimp connector for 6 gage wire and under, and I've not had a crimp come loose when using it. I do spend a little more on crimp connectors than most people (I flatly refuse to get "no-name" electrical parts!) which might have something to do with it as well.

I'll use solid copper lugs, tinned copper small connectors, and gold-"flashed" copper connectors for critical applications - no problems here. Electrics is typically worth spending a little extra money on anyhow...

5-90
 
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