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Scrap THWN for auto use on old 4X4? #50959 04/17/05 09:57 AM
Joined: Mar 2004
Posts: 32
Sparkeee32 Offline OP
Howdy! Simple question, Can I use Scrap THWN for wire within my rough and tumble 4X4 truck? THe wire is free scrap from work, the wire guages I'll match or upgrade from stock manuals. I'm not concerned with legal tech really, just in the real world application, safety, and flat out, will it work [Linked Image] Thanks! Brian Sparkeee24 P.S. any other ideas would be apretiated as well !

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Re: Scrap THWN for auto use on old 4X4? #50960 04/17/05 10:05 AM
Joined: Jul 2002
Posts: 680
walrus Offline
It will work but the insulation will crack after a while from my experience.

Re: Scrap THWN for auto use on old 4X4? #50961 04/17/05 10:21 AM
Joined: Sep 2001
Posts: 806
NJwirenut Offline
I used THWN to run power from the battery to an inverter in the bed of my PU. Has been installed for 4 years now, and still looks fine. YMMV. Secure it well, and use grommets wherever it passes through metal barriers.

Re: Scrap THWN for auto use on old 4X4? #50962 04/17/05 02:31 PM
Joined: Feb 2003
Posts: 687
Active 1 Offline
Make sure it's stranded.

I used it for some things under the hood and inside. I'm too cheap to buy battey cables. For a 6' #4 I think was $15 or more. I ran scrap #2 from 1 battery to a lug on the starter then back to the 2nd battery. It's a bit stiff. We used welding cable on trunk mount baterys befor. That works a bit better because it flexes more.

Depending on the car some came with some poor quality wire. I want to say that some conversion vans and RV's are done with THWN.

Does not hurt to upsize the wire. I use a lot of #12 just because thats what I have. The manufacture tends to size wires on the smaller side for cost & weight.


Re: Scrap THWN for auto use on old 4X4? #50963 04/17/05 04:52 PM
Joined: Jan 2003
Posts: 1,429
LK Offline
Good subject,

I would not use it under the hood, the temp rise is much greater then it can stand, we seen this in action when we had a car fire in the parking lot at a bingo hall, when she came out to look at what was left of the car, she made a comment about my husband just rewired everything, yes he did, all with thhn wire, it cracked and shorted, i assume with the engine heat.

Re: Scrap THWN for auto use on old 4X4? #50964 04/20/05 09:48 PM
Joined: Feb 2003
Posts: 687
Active 1 Offline
Ok, I'll admit THWN is not the best choice for under hood automotive. I still say it will be ok.

Some automotive primary wire is only rated for 80 or 90 C at 50v.

Most wire is run thru wire looms or wrapped in tape from the factory for additional protection. It is good to protect the wire in this way and secure it. Things can rub thru with vibration. One key is to keep the wires away from the more hot pieces like the exhaust which can run in the 400 F range or more if somethings wrong.

Everything except the battery cables is fused or has fusable link wires (except for a few slip ups from the factories). An electrical fire most likely is from a shorted batery cable or an unfused wire shorted. Too many people just hook on a wire to the battery. Also don't delete the fusable link (a short piece of smaller gauge wire by a power distribution point).

Some vehicles do run hotter under the hood like if it has a turbo. But for a typical POS it will last until the next thing breaks.

Auto wire distribotor spec's: [Linked Image]


[This message has been edited by Active 1 (edited 04-20-2005).]

Re: Scrap THWN for auto use on old 4X4? #50965 04/21/05 01:00 AM
Joined: Jul 2004
Posts: 9,541
gfretwell Offline
The big killer will be vibration. Even stranded THHN will not be as tolerant of movement as the regular fine stranded used by the manufacturer.

Greg Fretwell
Re: Scrap THWN for auto use on old 4X4? #50966 04/21/05 08:11 AM
Joined: Mar 2005
Posts: 53
highvoltageguy Offline
I used to work for a custom van customizing place in San Diego in the mid 70's and we used thhn/thwn inside the van, console wiring,lighting thru out van etc. all from a fuse block, as for inside the engine comp. did do much there. but I do have a old 65 ford truck and the old guy I got it from was JCWhitney crazy and he did lots of stuff, using thwn and it still ok and i've had the truck for 15 years now, and some of it is in the engine compartment.

Re: Scrap THWN for auto use on old 4X4? #50967 04/22/05 06:22 PM
Joined: Jan 2003
Posts: 1,429
LK Offline

The stranding is the problem, when the insulation splits, the stranding pushes out of the jacket, they are discovering this, with aircraft wiring that was built under mil specs., the older cables were bundled, and some of them laced, however small cracks, or tears can rupture under vibration, and a little moisture, and there goes everything.


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