73 GMC Truck Wiring Diagrams/Battery Cables

[Spool]

Hey guys.
73' C20 here.

I'm replacing the +/- cables from the battery and wanted to make sure I had the right gauge.
Taking a look at my Wiring Diagram book (X-7305; Picture attached)

It's showing:
2gauge from + to starter.
12gauge from - to sheet metal ground
12 gauge from - to engine.

Why two grounds?
What part of the engine do I ground the battery to?
What does BLK stand for?

[bd]

Both the positive and negative battery cables should be 2-gauge copper cables (not aluminum and not copper-clad aluminum).  The negative battery cable typically attaches to the alternator support bracket, but any clean connection directly to the bare metal casting of the block works as well.  However, do not connect the ground cable to an intake manifold bolt.  And, do not use star washers to attach any of the cables.  The 12-gauge ground attaches to the radiator support.  Adding a redundant 12-gauge ground to the right frame rail is a good idea.  In addition, make sure you have a 12-gauge or 10-gauge jumper between the engine (back of right cylinder head on a V-8) and the firewall sheetmetal of the cab.  The heavy 2-gauge battery cables are used for cranking the engine and charging the battery.  The lighter gauge (redundant) ground cables ensure there are uninterrupted ground paths available for the lights and the chassis and cab electrical accessories/appliances, etc.  "BLK" refers to black, the color of the wire insulation.

[Spool]

Thanks BD.

I had assumed BLK was black, but isn't it convenient to have you B+ cable to be red?
This was why I didn't purchase new cables at Autozone today. They had proper length in 2 gauge but nothing red; also they all came with preexisting connections which I didn't appreciate.
Would you happen to know where I could pick up 2gauge wire that was color coded and naked so I can make my own connections? I'll be trying Pep Boys in the morning.

If I read your response correctly, I would have 3 redundant grounds which are 12 gauge?
2 from negative terminal going to radiator support and another to sheet metal frame.
1 from back of engine block to the firewall (I have a V8, will I see an existing ground/bolt to go from or is this an extra safety measure?)

Thanks again BD. (Sorry for improper posting, I'll be more aware of the categories for future posts)

[bd]

What's everybody's favorite source for buying wiring/looms/etc.?

For short length battery cable runs try the various local parts houses for bulk cable sold by the foot.  For best results, firmly crimp the battery cable ends to the new cables before soldering with 60/40 rosin core solder.  Avoid acid core solder and acid flux as the acid continues to corrode the base metals.  Shrink seal the cable ends using dual or triple wall, adhesive lined, polyolefin shrink tubing.

Grounds are battery-to-engine (2-ga), battery-to-radiator support (10-/12-ga), battery-to-right (passenger side) frame rail (10-/12-ga), engine-to-firewall (10-/12-ga).  All the grounds described should be  preexisting with a possible exception of the B- to frame rail.

[Spool]

Thanks man.
I'll take a look at the engine to firewall jumper mentioned; I don't recall seeing one in the past.

Rosin core solder is something I've yet to learn, I'll try my luck at pep boys or home depot to have it cut to size. (Hopefully PepBoys, I don't see HD carrying it)

[Spool]

I may be over thinking this, but the terminals already installed on 2guage wire available at autozone and pep boys look like garbage.

Home Depot carries 2AWG THHN. Similiar to this: http://www.homedepot.com/p/Southwire-By-the-Foot-2-Black-Stranded-CU-THHN-Wire-20502199/204632781?cm_mmc=SEM%7cTHD%7cG%7c0%7cG-Pro-Services&gclid=CjwKEAjw4vzKBRCt9Zmg8f2blgESJADN5fDg2xkAkt0nEX12aqJ69m8g5nf3ESSeAvSxyu40mJa51hoCns_w_wcB&gclsrc=aw.ds

Copper is copper right? As long as it's 2AWG, this would do the trick?

[bd]

There is nothing wrong with being analytical.  Here are my thoughts...

THHN possesses decent abrasion, caustic chemical and moisture resistance, but is rated to only ~167° F when used in an environment that exposes the insulation to petroleum oil and coolant.  In addition, THHN is relatively stiff due to lower copper strand count, which might tend to concentrate flex at the tie points of the cable instead of dispersing flex evenly across the cable between tie points, resulting in eventual wire fatigue.  It is so stiff that I think you will be dissatisfied with it.

I recommend SGX or SGT battery cables, or substitute neoprene jacketed welding cable if you have it laying about.  SGX insulation is manufactured from cross-linked polyethylene, possessing exceptional abrasion, caustic chemical and moisture resistance, is specified for harsh marine environments and is suitable for operating temperatures up to ~255° F; whereas SGT is made from PVC thermoplastic, is rated for 185° F environments and is typical for automotive use - both are priced similarly and if readily available, SGX should be your first choice.  [You may find this short You-Tube video interesting:  All About Battery Cable: SGT, SGX & STX as well as SGT/SGR/SGX Battery Cable.  In addition, if you decide to fabricate your own cables, How to Make Battery Cables the Easy Way! is a decent "How To" for do-it-yourselfers who don't have the specialized battery cable crimping tools - my primary contention being the choice of heat shrink tubing in the video.  As previously stated, use dual- or triple-wall, adhesive lined polyolefin heat shrink].  However, buying the materials to fabricate your own cables is pricey when compared to buying prefabbed cables.  If you are merely adverse to the "look" of available prefab battery cables, you can always clip and replace the ends.  Frankly, decent cables from O'Reilly's or NAPA, etc. should suffice for a long while.

[Spool]

Thanks BD.

Ebay seems to fit the bill of allowing me to purchase just a few feet.
black - http://www.ebay.com/itm/302066246957?item=302066246957&viewitem=&vxp=mtr
red - http://www.ebay.com/itm/SGX-2-GA-gauge-BLACK-engine-starter-Automotive-alternator-battery-ground-cable-/291753839739?epid=782531951&hash=item43ede24c7b:g:4gsAAOSwKfVXJ3wC&vxp=mtr

I was surprised to see the Red cost 4 times the price of black but so be it.

I'll be doing this this week or so.
Do you think it's easier to drop the starter to re-cable it or try to get behind the headers as is?

[bd]

I was surprised to see the Red cost 4 times the price of black but so be it....

Do you think it's easier to drop the starter to re-cable it or try to get behind the headers as is?

The price differential is because the red SGX cable you linked is high strand count 2/0 (aka 00) gauge cable, not 2-gauge.  Red and black 2-ga SGX cable should sell at the same price from a given vendor.

Your question on ease of installation is difficult to answer w/o seeing the exhaust configuration with which you're working.  If the battery cable is in close proximity to the exhaust header, anchor it away from the exhaust and any sources of chafing using Adelle clamps, then consider thermally insulating it with Thermo-Sleeve or similar tubing.

[Spool]

Thermo Sleeve seems like a good idea considering it's only about an inch or two from the headers.

Thanks for pointing out the 2/0 vs 2.

I'm scratching my head on the availability of red though, particularly because in seeking Red for the B+ in any length turns up to be wholesale
opposed to BLK which is abundant per foot.

Let's say I go BLK for both +/-, of course I'll know which cable is which and I'm assuming a mechanic would as well.
I was thinking maybe Red electrical tape along the B+ cable but electrical tape is rated at 176F.
If I use BLK for both +/- and call it a day, I guess an extra safety precaution could be the B+ has the Thermal Sleeve.

[bd]

LOL!  Now, you're overthinking!      Even a noob mechanic should readily distinguish between B+ and B- cables, or (s)he should be doing something else.      

Black jackets for both cables are standard.  You can always use red, triple-wall, adhesive lined, polyolefin heat shrink to finish and distinguish the positive cable at its terminal ends if that custom touch is important to you.   

Still, if you're patient and search "SGX 2 gauge red," you are bound to have a few hits for cut-to-length or short-length cable (e.g., Wirebarn, AWC, Advance MCS, etc. - no endorsements expressed or implied).

[Spool]

Haha. Alright. Sold.
http://www.ebay.com/itm/SGX-2-GA-gauge-BLACK-engine-starter-Automotive-alternator-battery-ground-cable-/291753839739?epid=782531951&hash=item43ede24c7b:g:4gsAAOSwKfVXJ3wC&vxp=mtr

Thanks again man.

[Spool]

Cable arrived today; looks great.
Before I replace, I was curious to know if my starter stores a voltage at all even after disconnecting the battery? Any caution needed when touching?

[Spool]

dang, now I'm just embarrassed of my learning curve and condition of my wiring.
I've attached photos.

I guess first up, is I need to take the starter out to see what I'm doing.
Is it these two bolts on the bottom shown in my first photo only or is there a third?

The, on my Battery terminal, from this angle I notice there is a second connection asides from my B+. What is it and where is it going?
(The black one in the top of the second photo)

Lastly, my header has damaging my cable going to, shown in the 3rd photo. Is this the connection going to my solenoid winding terminal?
Clearly is still working and from past posts here I know it would have to be fabricated to be replaced. Could I insulate it with clean electrical tape and a thermal sleeve?

[bd]

I spy with my little eye... several "looming" issues.  lol

The wiring has been modified and shortcut.  Battery cable routing needs to be corrected.  You need to procure and install a starter heat shield (or, less optimally, wrap the individual header pipes in close proximity to the starter).

The starter does not retain any electrical charge.  The two 9/16" head bolts you imaged, fasten the starter to the engine - an optional third attachment point (a small support bracket linking the front of the starter to the engine block) is absent.  Before removing the starter or performing any wiring repairs, disconnect the negative cable from the battery.  I will follow up with more details, hopefully this evening.