The Stovebolt Site Forums The Shop Area The Electrical Bay Universal wire harness vs. Truck Specific for 51

Hello Stovebolters,

I'm starting to look at electrical harnesses for my 1951 3100 (1957 235 engine) which I want to convert to 12V and I was wondering if anyone has utilized the generic harness for chevy's from a place like Summit Racing versus the much more expensive truck specific harness.

Just wondering how well they work, how difficult are they to install and any recommendations on which one to buy or should I just cough up the money and buy the specific harness for this truck.

Just hoping to save some bucks for other parts.

Thanks for the help/advice.
Scott

I would purchase a harness made for the specific vehicle with all the wires the correct length and nothing left over for things you don't have. The one sold by Summit looks to be around $700 which is about the same as the specialty places.


YNZ Yesterday's Parts Complete reproduction wiring harness for all makes and models
http://www.ynzyesterdaysparts.com/
909-798-1498


Rhode Island Wiring Service, Inc. Wiring harnesses for all years, all makes and models
567 Liberty Lane, PO Box 434
West Kingston, RI 02892
(401) 789-1955
http://www.riwire.com/

It depends on how handy you are. I have used the ~$250 ones from Speedway and the ~$50 ones from Amazon. I have also bought rolls of wire from Waytek and done it completely from scratch.

The speedway ones are nicer because every wire is individually labelled every foot on the insulation. You do have to cut to length, put on the connectors, and figure out your own routing. I personally find that pretty straightforward, but I am an engineer by trade so your mileage may vary.

I do remember being pretty intimidated the first time I needed to completely rewire a vehicle. I pulled a painless harness out of the box and stared at the pile of wire for a while. Once I got down to it and started laying things out, it really wasn't that bad.

The other thing to take into consideration is if you are going to be adding any new features (power locks, new radio, turn signals, etc). The stock replacement harnesses I have seen do not have provisions for those, so you would have to figure out how to wire them in yourself. The universal harnesses will have turn signal wiring and extra circuits for whatever else you want to add.

The original, expensive type are not the way to go. Most are the same pvc wire as used in the universl kits, with cloth covering, no fuses, no expansion possibilities. Rip Off.

DIY does not save any money and collecting all the parts is a real hassle. many times you have to buy minimum orders with electrical supply companies. Depending on the era of truck. The kits have good packard 56 connectors. Semi era correct and necessary in some cases. Time to get rid of the inner fender terminal blocks also.

The way to go especially with a 12v conversion is a universal prewired fuse panel kit. Advise alternator at that time also. These harnesses are pretty easy to install. Many of us can help. I have much experience with them. Easy to install. Our old trucks are very simple. Very few wires.
Speedway has a 12 Circuit for $186. A 22 circuit for $203 (may be the best value). Amazon as low as $125. Jeggs, Summit, Classic Trucks, Painless, EZ Wire, AAW, etc. Don't buy from a funky place/guy.

These kits will need you to crimp. Good crimpers are available. Solder is not necessary with a good tool. These kit sellers all use basically the same quality automotive wire. The prices reflect number of circuits and the extras provided in kit. Just check out the literature for the one you wish to buy.
Most say do not support ammeter, some say don't support generators.

Probably repeated some of what Fibonachu said.

Yes I'm an aerospace engineer for the past 30 years, so not necessarily totally against installing this harness, just a little intimidated.

But I have done everything else on my truck myself so why stop there.

Based on the feedback I think I will go with the universal kit after doing some more research.

You have pointed me in the right direction and I know that if I have questions when the time comes, I can always reach out to folks here on the forum.

Thanks again and keep those wheels turning.

Scott

I was an AE at Georgia Tech for 3 years before I said "the heck with this nonsense!" and switched to IE!

Using this thread because it seems pretty germane to the original question.

One last moment of doubt before I hit “buy it now” on some wire and other supplies and there’s no turning back on my Johnny Cash Rewire project.

I have never been under the illusion that my completely DIY approach would save time or money. And I am still completely OK with that. It was more about the hassle of modifying a cookie cutter harness to accommodate the way I want this done. It was also out of resistance to taking the truck off the road for a few weeks when I had just gotten the truck on the road. Those factors are still in play.

However, I’ve now done enough reading, YouTubing, planning, etc…. that my understanding of 12v automotive electrical is at a completely different place than it was a few months ago. I am much more comfortable with the idea of modifying an existing harness to do things my way. Up to and including de-pinning and re-pinning a universal if I had to.

Anywho…

It occurred to me last night that the “where and how to mount” custom panel is probably the biggest remaining undecided. Having it out of sight, relatively easy to service…those goals are competing with the amount of space my custom approach will require. And boy, those universal 12-circuit kits sure are compact.

That’s a whole bunch of backstory to arrive at this question:

What is the lowest prices 12 circuit harness with a decent and verifiable wire spec?

I cannot find a universal that has a verifiably decent wire spec (GXL) for less than the Speedway 12 circuit @ $185. That would be the very most I’d care to spend, given the amount of modification I’m likely to do. I don’t want to go cheap and get a kit with wire of VERY questionable origin and quality.

I haven’t accumulated a LOT of stuff just yet, but enough that the cost of a decent universal would likely exceed what I’ve budgeted and priced to do it from scratch.

Scott -- You forgot to add the English Major Tech Writer who gets added to the team to completely rewrite the Tech Manual after feedback comes in from the Fleet that non of the O or I-level maintainers understand a word of it.

Fib -- Oh no ... an engineer with DAWIA training is a scary thing. To do the light bulb acquisition correctly, you need to set up a 35,000 member Systems Command, dotted line connected to a Program Executive Officer -- Illumination, Identification and tracking Light Emission Device Programs, to administer the sub-level Integrated Product Teams required to accomplish the Research, Development, Test, Evaluation and Acquisition (full lifecycle management) of the "Bulb, Light, 1 ea." And don't forget the Oversight. We can't just let these people run out and buy light bulbs will nilly, you know. And if you decide on sole-source, please detail your FAR Exemptions justification.

If you were DAU Level III certified, you'd know all this.

Scott -- I hope you have been offered the available options with enough detail to make an informed decision that suits *you.*

As for me, I am still toying with the idea of doing my own rewire from scratch. But my truck is in original 6-volt configuration and would be simpler to go that route than anything modified or custom.

It *can* be intimidating at first. But I've done a couple now (rewires -- both modern harness and a repro original from Vintage Wiring of Maine) and if you just start in and go one system at a time, its not hard. Kinda fun, I thought.

Regards,
John

I bought one of the $25 amazon universal harnesses (18 circuit?) last year from morbid curiousity. I expected to return it as trash, but I was curious and it ended up being very nice. Let me dig out the paperwork and see if it had any of the wire types markes on it.

By insepction the insulation was appropriate thickness, the wire was flexible and high-strand, the crimps at the fuse block were solid. I am intending to install it in my daughter's jeep this summer.

I've used two of those Amazon wiring kits now with great success. Currently doing a bumper to bumper rewire on our first fire truck (1952 F***) with one and it's got such long wires I can almost reach the rear bumper with it. The front clip wiring is long enough you could easily move the fuse box anywhere you wanted if you had a panel truck, for example. There are circuits that become handy "extras" (assuming you aren't using power locks or windows, fan, etc) for any additions you might want to add later. They even come with headlight plugs and the standard blade type GM alternator plug (for the 3 wire style).

The current kit I'm working with actually has all the wires LABELLED which can save some walking back and forth (especially on a large vehicle). The whole thing was under $200 Canuck shipped!! About the same as taking the family to Boston Pizza for dinner.

Having also done a few from scratch, quite honestly I prefer these kits. Might move up to a more expensive kit for the next one only to compare.

JW, the speedway will be the best choice for the money. Sold by Speedway or by Amazon. Same price. You ALWAYS want to mount the fuse box upper left of left foot on inside of firewall, if at all possible.

There are cheaper kits, but in my opinion from unknown sellers and/or makers.

Don't get too wound up in wire specs, they are all suitable for our trucks. Crosslinked or PVC. Not sure what you meant by the need to de-pin and pin. Nothing is terminated (pinned) but the fuse box end in the kits. The YNZ type would be very difficult to modify and defeats the purpose.

No one knows what prices will do now-a-days so "bite the bullet" and "pull the trigger" if you are ready to wire. We are here to help. Wiring is best done when most other restoration/refurbish/preservation tasks are complete and all electrical components are in place.

I have used 2 painless harnesses, one specific one universal. Very pleased with both! They also have tech support which was helpful. I think they are a bit more expensive.

John, They're called work-arounds. When that Polaris with snow tracks has to be at the bottom of the mountain for a highway patrol escort to the top of the mountain, because they're all snowed in up there, and you're an hour and a half away from the drop off point, and they have to be there in 30 minutes or so, you just find a way!

As for the wiring, I still do it all from scratch, just because I enjoy it! Whether the vehicle hates me or not!!

My “de-pin” terminology is probably wrong. I was presuming that the terminations into the universal fuse box itself, could be removed, and replaced with a like fitting and different wire, etc.

Is that assumption incorrect?

Between the positive comments about the comically cheap Amazon harnesses, and Bartiminos comments that all the wire is fine….my wheels are turning again.

Daggumit. Anyone else afflicted with the “overthink everything” gene?

You would never want to, or need to, mess with those in-box terminated wires. You can terminate the other ends of the wires from the fuse box pretty much anywhere you want.

You have underestimated what a weirdo you are dealing with. I’m asking…is it possible?

Yes it is possible. I have done it to increase the wire gauge on a given circuit. If you do that, make sure all of the wiring feeding that circuit is also beefed up appropriately. You will also need to identify the correct terminal for that particular fuse blot. Again, doable but a pain.


Curious why you say that. I have mounted them in a variety of places based on convenience and never had an issue. The older Chevrolet vehicles mounted them there originally, but newer vehicles put them in all kinds of places.

EDIT: I will come back and second one of Bartamos's other comments. If you get the Speedway kit, you know exactly what you are getting and I have personally used at least 5 of them and had zero issues. I know others have posted that they also used the Speedway kits and were happy with them. Is that guarantee worth the 5x+ cost? That is up to you. I got one of the Amazon ones to try because their return policy is good and I trusted myself to be able to inspect/evaluate it. Based on your other posts, I am not sure you have that confidence.

The types of insulation on any of these is going to be irrelevant in this application as long as it is applied properly (which you can tell by pretty quick visual inspection). The places that I get concerned are the crimps at the terminated ends (they should be tight, clean, and uniform) and the quality of the wire itself. Low quality harnesses will use low strand count wire (which is prone to cracking and breaking in a vibration/flexing environment) and/or aluminum wire that might or might not be coated in copper to make it look the right color. To check that, you can either carefully shave a strand down to nothing and make sure it is copper all the way through or cut it with a sharp implement and inspect the end to see if it is a uniform material. I prefer shaving because the copper from the outside can stretch and cover the end of a cut well enough to make it difficult to tell.

[quote=Fibonachu]

Yes it is possible. I have done it to increase the wire gauge on a given circuit. If you do that, make sure all of the wiring feeding that cicuit is also beefed up appropriately. You will also need to identify the correct terminal for that particular fuse blot. Again, doable but a pain.
––––––


Exactly.

JW51: I will caveat my earlier statement with the fact that I only needed to increase the gauge of a circuit because I was doing something strange with it. If you are wiring it up essentially stock, then you won't need to fiddle the block.

I take it you mean removing the pin and re-pinning with larger gauge wire? I also do this in certain cases - usually when using the universal kits; as sometimes it just makes more sense (and you end up with a cleaner install). In fact I did it over the weekend on a circuit for our fire truck.

I have a selection of the correct replacement connectors that lock in the box or plug. Use the right tools and take your time, it works fine. x3 on making sure all the wiring is upgraded.

Yup. I have mine mounted center inside my firewall. Most current vehicles have them split between the engine compartment and inside the cab. Some era Ford trucks will have them in the passenger footwell, cowl side and some Escapes and Fusions, etc, have them on the passenger side trans hump forward. It's always an adventure these days to initially locate a fuse panel. I've even found some behind glove boxes.

I’d need to study the diagram for one of these things to figure out what, if anything, I might modify. Just wanted to know it was an option.

Wanna keep my ancient turn signal switch, relay the headlights, keep the Gen/VR/Ammeter. Maybe all that is easily done with no mods. I’d just have to play it by ear.

Turn signal switch won't be a problem. You will have to clip off the column connector (if your kit has one) but if you are using the original column you would do that anyway.

Headlight relays shouldn't be necessary with a new harness, but that is also easy to do (just run the headlight feed from the new harness into the coil pin on the relay).

The ammeter should be pretty simple, but without a wiring diagram in front of me I can't tell you exactly what to connect where.

I am not familiar enough with the generator control wiring to say how to do that. I would ping Hot Rod Lincoln as a local expert on generators and voltage regulators.

Jegs has a nice writeup with diagram for a few charging circuits: https://answers.jegs.com/blog/10405...-for-universal-20-circuit-wiring-harness

The harness shouldn’t really care about the generator. Disregard that.

JW-area51

.......don't think you are fooling anyone by calling your procrastination........."overthinking"

Bartamoses

If you are curious, the technical term is "analysis paralysis".

I am quite familiar with this problem. Balancing budget with effort with quality with risk can quickly become overwhelming. Add in the various bits of side information that the different helpful people here offer and it all twists up in your head and feels overly complicated.

When I am struggling with it, I find it helps to take a step back and revisit the question: what am I actually trying to achieve? I often find that going back to that basic question helps me clarify my goals and identify my path forward.

The harness does care about the generator/voltage regulator if you are planning to replace the wiring for them. Not sure of you saw the Jegs link above, but it has recommended wiring schemes for different charging circuits. I would compare those to your factory diagram before taking them as gospel though.

Ordered a pile of wire tonight. Stay tuned.

Inquiring minds need to know: which solution did you choose?

Im going the DIY route.

To the analysis paralysis comments, that’s all very true and fair.

But I actually ENJOY researching and analyzing and trying to find the best possible solution that balances all constraints. It’s fun for me.

Case in point- the wire order I placed is with the intent of doing a GM-ish color scheme. Even though a 1951 truck didn’t have modern color wire and I plan to hide most all of it in loom. I figured someone in the future might appreciate the effort. Combination of GXL and TXL wire. Found a really good deal. All this prework had been done before I had my moment of doubt yesterday regarding a universal.

Gauge was considered based on amp/gauge/length charts. Erred on the large side for simplicity and safety factor. Lengths should allow for some waste, but not a ton of leftover. I’m sure I didn’t get it 100%. Probably have to buy a little of this or that. Still need to source some beefy stuff for the main power distribution. Probably source that locally.

How’s that for a geek-out on wire purchasing?

Seems like a good plan. What are you using for a fuse block/power distribution unit?

Out of curiousity, where did you order the wire from? I usually get my bulk wire from Waytek, but would be interested in another source.

Going to answer your question in my other thread, Fibonachu. I feel like I’ve severely hijacked this one.

Scott4Chevy I just got over the 4 pages of wire loom discussion,no one said a word about the original wiring being twice as heavy as needed if your going to 12 volt. If you are lucky that no one has butchered into the under dash loom,then you can repair what is accessable and end up with a good system. On this sight they will spend a fortune to keep other systems "stock" so why not wires ?? In 50 years and 30 trucks have never "burnt" one up. Oh well,just a flunky out here in the calf lot no degree's learned at the hands of other butchers. My .02 Cents Good Luck don't "let the smoke out" !!