Big 3 cable upgrade crashes into ohm's law

[PlayingWithTBI]

Thats looks great. Was it hard to install?

My son did it for me since I was working 6 days+ a week at the time. I dropped it off at his house and he got it done in a couple weekends. IIRC the only sensor he used with the kit was the CTS in the head. I also bought the dimmer control for it so I can dim the cluster separately from the rest of the dash. Note: when I bought mine it came with both blue and teal colored displays. I see now you have to order which one you want. I probably should have gone with teal (to match the rest of the convenience center) but, I like blue better, ha ha.

 

[Ken K]

That's a first-post for the ages. Detailed, visual aids, descriptive, and with outside references to allow independent confirmation. Congrats!


Sure about that?

I dicked with the battery cables on my '97 K2500 last summer. I'm thinking they were more like 4-gauge than 2-gauge.

But I've got no service history on this truck--maybe someone replaced the OEM cables already.

This is timely, 'cause just a day or two ago I shot my mouth off about 4-gauge cables being fine, with 2-gauge being more than adequate. But if the OEMs are using 2-gauge, I'd better look into the load they're supporting. Maybe it's higher than I'm expecting.


I was pretty unimpressed with GM wire-harness gauge size when I was measuring voltage-drop in the fuel pump circuit of my two Luminas. They measured the same at every test-point.

I'd measure a tenth-of-a-volt drop everywhere I tested. The total drop from alternator + to the last access point before the wires went up and over the tank, was a full two volts on the supply side, with another volt on the ground side.

The alternator was producing 14.2 volts, the fuel pump was running on 12.2 on the supply side, with another volt lost on the ground side--total fuel pump voltage was down to 11. I did some digging into gauge size vs. power draw. GM was using "16 gauge" (Metric equivalent) wire on a circuit that industry standards would call for 12-gauge wire.

Rat Bastages!

OTOH, either car has enough fuel to hit the 112 mph speed limiter programmed into the computer.


You talking about those ground straps from cowl to engine, or maybe from body to frame? Looks like about 1/4" wide?
GM uses piece-of-**** braided ground wires because the electrical load is so tiny, AND those wires are larger than they appear.

The primary ground wire is from the battery - to engine; and the only reason it's huge is because of the starter motor.

A 4-gauge ground from the firewall to the back of the head is exactly the sort of enormous that the original poster warned about. There's no harm to it except to your wallet. There's also no benefit to it. Same with the braided ground strap between body and frame, and any other place they used those thin braided straps. There's just not that much load on 'em.


I have a very ratty '66 Toronado. Got tired of the windows not going up 'n' down. Pulled both door panels off, re-wired all the stuff going through the door hinge area. Had to go way up under the dash to get rid of all the green copper so I could solder onto copper-colored copper.

I crimped and soldered everything. Got rid of a small mountain of hard-insulation, green copper in favor of whatever brand new, supple wire was on the rack at my local NAPA. Windows would go up and down real nice. The lights in the doors were bright. I'm real pleased.

Come out to the car about six weeks later, start the engine...and I see sparks under the dash near the park-brake area. Friggin' squirrels had eaten all the nice supple insulation off the new wires, left the old wires alone.

It's not just GM's wire insulation.


Who cares about inrush current? The inrush current doesn't last one second. Doesn't last long enough to warm the cable or cause any issues.

By the time the ammeter can get a reading on it, it's ~200 amps or below. Some big-block Olds and Caddy might go to 225 amps. The newer mini-starters are lower than that--150-ish.

Worst-case would be a winter situation, where the oil is thick so the engine is real hard to crank. But there's still little concern about the amperage heating the wires because
1. Wire temperature starts off as cold as everything else, a cable at -30F can have considerable temperature rise before the insulation is in any danger.
2. The wire is somewhat more efficient when cold, and
3. The starter is likely to melt before there's any danger to the cable itself.



Short story:
1. There's no reason to go nuts with gauge sizing, but in select applications increasing the gauge size can be beneficial, especially if you're adding load the engineers didn't account for--crazy stereo amplifiers, more-powerful alternators, etc.
2. The voltage-drop test tells all. If your voltage drop across a loaded circuit is acceptable, upgrading the gauge size does nothing useful. The trick is to assure that the circuit being tested is appropriately loaded when the test is performed.

 

[Ken K]

That's a first-post for the ages. Detailed, visual aids, descriptive, and with outside references to allow independent confirmation. Congrats!


Sure about that?

I dicked with the battery cables on my '97 K2500 last summer. I'm thinking they were more like 4-gauge than 2-gauge.

But I've got no service history on this truck--maybe someone replaced the OEM cables already.

This is timely, 'cause just a day or two ago I shot my mouth off about 4-gauge cables being fine, with 2-gauge being more than adequate. But if the OEMs are using 2-gauge, I'd better look into the load they're supporting. Maybe it's higher than I'm expecting.


I was pretty unimpressed with GM wire-harness gauge size when I was measuring voltage-drop in the fuel pump circuit of my two Luminas. They measured the same at every test-point.

I'd measure a tenth-of-a-volt drop everywhere I tested. The total drop from alternator + to the last access point before the wires went up and over the tank, was a full two volts on the supply side, with another volt on the ground side.

The alternator was producing 14.2 volts, the fuel pump was running on 12.2 on the supply side, with another volt lost on the ground side--total fuel pump voltage was down to 11. I did some digging into gauge size vs. power draw. GM was using "16 gauge" (Metric equivalent) wire on a circuit that industry standards would call for 12-gauge wire.

Rat Bastages!

OTOH, either car has enough fuel to hit the 112 mph speed limiter programmed into the computer.


You talking about those ground straps from cowl to engine, or maybe from body to frame? Looks like about 1/4" wide?
GM uses piece-of-**** braided ground wires because the electrical load is so tiny, AND those wires are larger than they appear.

The primary ground wire is from the battery - to engine; and the only reason it's huge is because of the starter motor.

A 4-gauge ground from the firewall to the back of the head is exactly the sort of enormous that the original poster warned about. There's no harm to it except to your wallet. There's also no benefit to it. Same with the braided ground strap between body and frame, and any other place they used those thin braided straps. There's just not that much load on 'em.


I have a very ratty '66 Toronado. Got tired of the windows not going up 'n' down. Pulled both door panels off, re-wired all the stuff going through the door hinge area. Had to go way up under the dash to get rid of all the green copper so I could solder onto copper-colored copper.

I crimped and soldered everything. Got rid of a small mountain of hard-insulation, green copper in favor of whatever brand new, supple wire was on the rack at my local NAPA. Windows would go up and down real nice. The lights in the doors were bright. I'm real pleased.

Come out to the car about six weeks later, start the engine...and I see sparks under the dash near the park-brake area. Friggin' squirrels had eaten all the nice supple insulation off the new wires, left the old wires alone.

It's not just GM's wire insulation.


Who cares about inrush current? The inrush current doesn't last one second. Doesn't last long enough to warm the cable or cause any issues.

By the time the ammeter can get a reading on it, it's ~200 amps or below. Some big-block Olds and Caddy might go to 225 amps. The newer mini-starters are lower than that--150-ish.

Worst-case would be a winter situation, where the oil is thick so the engine is real hard to crank. But there's still little concern about the amperage heating the wires because
1. Wire temperature starts off as cold as everything else, a cable at -30F can have considerable temperature rise before the insulation is in any danger.
2. The wire is somewhat more efficient when cold, and
3. The starter is likely to melt before there's any danger to the cable itself.



Short story:
1. There's no reason to go nuts with gauge sizing, but in select applications increasing the gauge size can be beneficial, especially if you're adding load the engineers didn't account for--crazy stereo amplifiers, more-powerful alternators, etc.
2. The voltage-drop test tells all. If your voltage drop across a loaded circuit is acceptable, upgrading the gauge size does nothing useful. The trick is to assure that the circuit being tested is appropriately loaded when the test is performed.

There is no reason to go big unless needed. Being man made, nothing is perfect. I chose to test a circuit with voltage drop. A terminal, fuse or switch will have voltage drop. A little is acceptable as using “Ohms Law” the sum total adds up to be more than the supply. I did not read about placing a negative cable on the back housing of the alternator where negative is produced. There is an unused bolt bolt back there. I would be running to the engine & battery. You can make connectors from copper pipe and imagination. Dielectric grease, star washers and sticking to “Best Practices” is best. A negative wire from a MAP or TPS is dedicated to where? The ECM/PCM right. How does it back to the battery negative? Generally, a schematic shows “G100”. Isn’t that the engine? What grounds the engine to the battery negative? Painted block & bolt? Factory acceptable voltage drop is 0.400 amps! Higher amps like lift gate or snow plow, it goes up!
So, clean it up before complaining. Electrical spray cleaner, scotch-brite, star washers, solder every replaced or existing connection like the woven grounds. If you have a 400 watt soldering gun (SnapOn R450B) I purchase a new 400 watt tip in Dec. 2020 but I didn’t look for the kit. Get solder & acid because it bites thru oxidation. Do all or that, then do “Voltage Drop”. Lots of videos.
Want better battery connectors or “Oxygen Free” copper wire? Visit knewkoncepts online as it is primarily a stereo store but good coonectors, wire doesn’t know what is hooked too! Ohms is fine, if you do the Ford wiggle test.

 

[Schurkey]

I did not read about placing a negative cable on the back housing of the alternator where negative is produced. There is an unused bolt bolt back there. I would be running to the engine & battery.

There's no ground cable at the alternator on many vehicles, because the metal brackets holding the alternator are the ground path. Steel is a crappy conductor...but there's lots of it, and alternator output on average is fairly low, compared to, for example, the starter motor.

You can make connectors from copper pipe and imagination.

...and a hammer, and a drill. Done that.

Factory acceptable voltage drop is 0.400 amps! Higher amps like lift gate or snow plow, it goes up!

VD tests measure voltage, not amperage. You mean 0.400 volts.

Thousands of years ago in Trade School, I was told that 0.5 volts of VD on the starter +, and starter - was acceptable. I was told that 0.25 volts of VD was acceptable for the alternator + and -.

TYPICALLY, you either see nicely under those figures, or you see substantially more. I can't remember a time when I was right at or near those limits.

So, clean it up before complaining. Electrical spray cleaner, scotch-brite, star washers, solder every replaced or existing connection like the woven grounds. If you have a 400 watt soldering gun (SnapOn R450B) I purchase a new 400 watt tip in Dec. 2020 but I didn’t look for the kit. Get solder & acid because it bites thru oxidation.

Acid flux on electrical soldering is a bad idea. The acid eventually causes the corrosion you're hoping to get rid of.

Acid flux when soldering copper plumbing works pretty good. The corrosion layer tends to be thicker; as is the overall thickness of the tubing. The acid is neutralized long before it can corrode through the tube--unlike thin wires.

My bigass soldering iron is an ancient WEN Model 450. Has three interchangeable tips; low-watt of maybe 75, medium of 250, and the big guy at 450. VERY nice gun, from a time when WEN build some decent equipment.

Called WEN about twenty years ago, looking for a new "big" tip. Discontinued; they had what stock was on-hand and then there'd be no more. I bought multiple tips of the varieties they still had. Went back later to get even more--and they were sold-out. Damned shame, that was a real nice soldering gun. (I still have a few spare tips...I'm set for awhile yet.) As a bonus, the internal windings are huge enough to test ignition pickup coils, so I can do some ignition diagnosis with it, too!

Visit knewkoncepts online as it is primarily a stereo store but good coonectors, wire doesn’t know what is hooked too!

As long as the insulation will withstand the automotive environment. Some insulation gets touchy around winter weather, high under-hood temps, etc.

I'm thinking there's Industry Standards for the fire-resistance of automotive wire that "stereo wire" doesn't have to meet.

Be careful.

 

[Ehall8702]

Cannot upvote this one enough.

Somewhere along the lines I missed the fact that we were talking about the older style headlights? My 97 and 98 have oem light fixtures with 4 sided 6000k leds, pattern is nice and tight, distance is great and the 6000k is nice, works well for reflective lines nd signs. Have great experiences with em and everyone I put em in for agree so far, but we are waaaay out in boonies, ALOT of pitch black roads for miles and not ALOT of traffic.

 

[GMTMark]

The original post is quite informative and does demonstrate that factory wiring is good for factory vehicles. I don’t think there’s much if any problem with these trucks except for some reason many electric fuel pumps tend to burn up the harness closest to the pump. AC and many others include a new harness with heavier wiring with new pumps. This has been one area where GM underestimated the demand. I had a 2007 Impala that the headlights would flicker. Under warranty they replaced part of the harness with heavier wiring. The factory is not going to put bigger wire than needed because of expense and weight. That being said, any weak point can give way to age no matter how well it was calculated when new. Automotive wiring will certainly give problems after a few years and, yes, the engineers do cut it too close at times with little or no room for modifications. My opinion and my experience.

 

[Schurkey]

My main beam flash (pull to pass?) has never worked and I intend wiring it to work with a momentary switch that I already installed on the dash as an interrupter to the fuel pump for when I'm running on LPG.

This switch just happens to have an additional terminal which is live via the momentary position. Power 'in' is from the signal from the PCM to the fuel pump relay. Not seeing any problem there but, with the headlights on and switched to mainbeam this switch will see a voltage from the signal to the relay all the way back to the PCM.

Could back feeding the PCM fuel pump control circuit cause any damage to it? Is a third relay safer?

Perhaps I'm misunderstanding your power routing.

Power "in" is intended to drive a fuel pump relay control winding? You're going to use it to power the "flash-to-pass" high beams?

Wild Guess: Headlight high beam will grossly overload that circuit. High beams will draw something like 12 amps.

I bet all you really need is a properly-working headlight switch.

 

[Pinger]

Perhaps I'm misunderstanding your power routing.

Power "in" is intended to drive a fuel pump relay control winding? You're going to use it to power the "flash-to-pass" high beams?

Wild Guess: Headlight high beam will grossly overload that circuit. High beams will draw something like 12 amps.

I bet all you really need is a properly-working headlight switch.

Just deleted my post before yours posted.
Won't matter as when the mainbeams are on via stalk, flash switch wont be conducting so no back feed.
It's only a switching signal to a relay - no more current than that.

You're right though, a properly-working headlight switch would solve this - if one was at hand.

 

[Pinger]

Did the relay mod and it dawned on me I'd be as well go 4Hi while I was at it.
Took on board everything mentioned on this thread and went the PWTBI three relay route and to avoid fuses popping too easily and swerving contact breakers I used a 20A fuse for each of the low and main beam circuits figuring that I may not be protecting components but avoiding any fire risk.

Mounted all of that in a water proof box which sits in front of the battery (in the dead space there) to minimise the cable lengths between battery and lights. Broke into the passenger side light cables for signals and just cut them as close as possible to their plugs to join the heavier cabling.

All done - except I didn't get my flash to work because for some reason the intended switch isn't working. It'll wait.

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[alpinecrick]

For corrosion under the hood, it's about maintenance. When we go to the manual carwash--you guys don't use those semi-useless automatic carwashes, right?--open the hood, leave the motor running and wash the engine compartment, including the parts of the frame and suspension that are accessible.
This goes a long ways towards thwarting the corrosion on things like the flat ground straps from head to frame and frame to body, along with other plastics and such.

Also, wash under the truck, especially the wheel wells and the lip on the quarter panels, and the bottom curved portion of the body where mud can collect, like the cab corners.

As time goes by I've learned a lot of the "failures" on these trucks are an absence of maintenance.