Technical Painless Wiring Warning

I'm not one to raise meaningless alarms or bash good products, but this can't be ignored. I've been PMing with a member about some wiring questions he had, and he described how Painless recommended connecting power to his fuse panel. I told him that what he said made no sense and he responded by posting this diagram out of the installation manual. For those who want to check, he has a 10102 harness and you can download the manual. This is the diagram....


The maxifuse they furnished is a 50 amp, and the 915, 916 and 960 wires are all #10 as far as I can tell from the manual wire index, which is what the member told me they were. This is some scary shit....

I've talked about overcurrent devices on these type feeds several times, and that's not even the worst part of this. There's multiple things wrong here, so let's see who has been paying attention. As an exercise for the students, who can point out the 'wrong' things? As a starter clue, what wires is the maxifuse fully protecting?

I'll check back later and hand out 'grades'....

 

I have heard quite frequently, that they are anything but painless.

 

50 amp? Top of my head says 8 gauge maybe 6, have to look it up

 

Well I was bad in school,, but it looks, to me, like 960 the 8 gauge and 915 all feed the fuse block

 

The Maxi Fuse is protecting the battery from a dead short!!!

10 gauge wire is rated at 30 amps and the 8 gauge "main feed" wire is rated at 40 amps.
So the fuse only needs to be 40 amp to protect the circuit [from the Alternator over charging with a flat battery] This should be a fusible link

By splitting the Alt wire into 2 x 10 gauge wires effectively doubles them to a 60 amp capability .

So the alt can be cranking out 60 amp but only 40 amps gets back to the battery, and the extra 20 amps could be consumed by the vehicle accessories [only 10 amps gets back to the battery via the 915 wire through the fuse block , and 30 amps via the 960 wire]

What we don't see in the above schematic is the connection between the 915 and 916 wire . I assume it is on a common bus.
If you use a fuse in the 915 wire, and it blows , it would instantly turn the 960 wire into a "fusible link"

You could achieve the similar results changing the 960 wire to 8 gauge and eliminating the 915 wire totally BUT this would limit the Alt output to 40 amp instead of 60 amp total [assuming the accessories is still consuming 20 amp, then only 20 amps gets back to the battery ]

The rating of the harness is based on "draw" or load! [not Alt or battery output]

 

960 red provides a path around the fuse. It provides zero protection.

 

Subscribed, as I have a car fitted with that stuff!

My answer to the opening question (which wire is fully protected) is the red 8 ga betwixt starter and fuse.

Chris

 

Oh heck. I read the question wrong.
Back of the class for me.

 

The 960 only provides a path around the fuse back to the battery
But there is a maxi fuse is between the 960/ 916 wire and the starter/battery "take-off"

The 915 and 916 wire should be joined by a common bus inside the fuse block [effectively being another direct path ,the same as another 960 wire]

Anything that is fed from the fuse block should be either switched or 12v constant AND fuse protected.

You could remove either the 915 or 916 wire [but not both] and the whole harness would still work OK.
Having both these wires gives the Alt charge a 2nd path back to the battery [and 2 paths to the fuse block] therefore having more capacity under load.

 

Thank you kindly Crazy Steve for posting this - Bubba looking to start wiring da A soon - and being Bubba - don’t need surprises or problems with the electrical wiring - don’t want da A to go up in smoke

 

Most obvious to me is that the maxifuse has a higher amperage rating than the lowest-rated part of the current path it's in?

 

I too am using this wiring harness. I haven't gotten to this point in the install yet and I would like to know the answer here as well. I can pretty much handle everything else building my car, but wiring is like voodoo to me!

 

Steve, hand out grades? you do know that ampacity of auto wiring is not based on building wiring.., 12 gauge 20 amps, 10 guage 30 amps and so on....

 

The fuse is useless. It'll break current from the starter to the system, that's it. The alt is still connected. Also if it blows there's no "excitement" element to allow the alt to charge as current to the battery is outta play if the fuse pops.

For extra credit, what we do here isn't mega OMG alky or nitro mags, double throw down electronic injection and managment, we're mostly building simple hot rods. This get up is as bad as the latest fashion of using relays for EVERY-FUCKIN-THING in spite of cars living twice some member's lives never having em. "The more they complicate the plumbing, the easier it is to stop up the drains." Montgomery Scott, Chief Engineer of the Enterprise. We keep getting waves of you gotta and I heard and how they. No. In fact, fuck no. Maybe I'm fortunate insofar as a background in restoration has given me the discipline of simplicity and necessity. Or maybe I have to ignore what was and do the popular approach. Nah, nothing has had issues in 40 plus years so far. I'll stick with what works.

 

Also I like sending the current from the alternator directly to the battery to help filter possible noise in my radio.

 

Yeah, no good the battery line goes pop if the engine is running.
Not so bad if all you've got is filament bulbs and points+coil.

Introduce alternator power without the battery to smooth the output- you should see just how noisy the voltage supply is with little to no load.

Couple whatever fault blew the 50A with any electronics and that harness will toast them, too. Ask me how I know.

 

I don’t want to be a contrarian so just going off my personal experience I had a painful time installing it because it was universal so I had to really remind myself it’s not factory replacement. Last one installed was on a dodge truck went well but was not wired like dodge. I looked at it as like chopper wiring on a motorcycle. I did start building my own harnesses but the painless wiring worked for customizing my own electrical needs. But it was a painful painful experience with their instructions lol

 

I don't know the answer Steve...but a few things to consider:

1. Not shown, but mentioned above, is that it's very likely that 916 and 915 connect directly to each other inside the Fuse Block.

2. There is no mention of acceptable temperature rise of the wires in this scenario. If you're using the NEC recommended ampacity for wire, maybe it's not applicable in this case? maybe it is?

The only real trouble I've ever had with a painless harness was badly crimped terminals, but that was a long time ago, and I haven't bought any of their products since then.

 

Rebel. The end.

 

I wired a car like this using a painless kit close to 10 years ago. Zero problems. But what do I know?

 

This is why i build my own harnesses. Yes this will work, but if the car is running and it blows the maxi fuse, as long as the alternator is operating properly it will continue on running. Wire 915 should be run directly back to the post on the starter and be 8 gauge. Wire 960, while I don't really see a need for it, should be eliminated, but if you must keep it should at least be moved to the other side of the maxi fuse to protect the harness and fuse block upstream from the maxi fuse. I used one painless set up on my 64 Buick, I was not overly impressed. Bad crimps and strange diagrams like this led me to never buy another one.

 

@Dyce you have a radio in your ride? I gotta step up. Sometimes my glasspacks lull me to sleep...

 

Don't forget that wire ampacity charts are for conductors grouped together, or in a raceway. Wire ampacities in "free air" are much higher than wires grouped. So in the case of a car it depends on how you route the wiring, and ambient temps around it. This is why electric providers are able to run such small overhead wiring to your home, or neighborhood and get away with it.
The 960 wire is protected by the Maxi Fuse, but the fuse should be as close to the starter as possible or the small wire feeding that fuse is unprotected. How big the wire is to the maxi fuse and after will determine if it's too small or not.

 

Working only from pic provided I’d move 960 to 8 gauge side of fuse. Then use 915 as voltage sensing wire for alternator. Again, I’m working off of “only” what you show here Steve.

 

That my take as well. But with out unit in hand to really see?

 

X2

 

Ditto here, came away with a better understanding of electrical. I did have to add a plug in diode at the alt so it shuts off.

 

Painless used to be, well, painless. Now the pain is compounded by the cost and unnecessary circuits and processes. Keep it simple, good grounds, proper wire sizes, done.

 

My wiring harness while similar to Painless, is a different brand, and has the wire from the alternator powering the fuse block through a circuit breaker. The instructions also provided for an additional 10ga wire that goes directly to the battery if an alternator bigger than 60amp is used. That wire is short. Maybe 18 inches long. I also sleeved it.