73 GMC Truck Wiring Diagrams/Battery Cables

[Spool]

Just ordered the parts and tools.

My confusion with the pink res wire is the set up. Originally, Pink was/is the source to a split going to the starter and the distributor.
But if the source is resistant, how does the distributor compensate for the wasted power? Also, does the distributor have two connections under the cap? One for spade and one for 56 Series?
In the end, what should this wire configuration look like when I approach it?

Also, had a thought while browsing for thermal sleeves online.
Considering my headers are rusty and not particular nice to look at. Could I use thermal wrap to wrap the headers?

[blazer74]

12 volts from the starter for starting via the yellow wire only for starting.

Pink Resistance wire takes over for normal run to prevent burning the the points.
Points don't require full 12 volts.

The other terminal on the distributor cap is for the tach if used.

[bd]

Great questions!

Here is a more thorough discussion.  Conventional ignition and High Energy Ignition (HEI) systems are different technologies, having different power requirements.  Conventional ignition uses a mechanical switch (the points) that directly cycles ignition spark to the plugs by turning power to the ignition coil on and off.  HEI relies on a magnetic pulse to trigger a transistor that controls power to the coil.  With conventional ignition, coil control is mechanical (the points).  With HEI, coil control is electronic (pickup coil and module).  Mechanical points arc when they open, resulting in wear from burning and pitting.  HEI doesn't suffer from internal arcing, so there is no wear.

To extend point life, conventional ignition restricts current flow through the points and coil to ~3 amps by limiting the voltage applied across the ignition coil primary winding to ~8.5 volts - which produces reliable spark energy to about 4,500 engine RPM.  On the other hand, HEI doesn't suffer from the limitation imposed by point arcing, hence, HEI earns no benefit from limiting coil current.  Instead, HEI applies full primary voltage (~14 volts while the engine is running) across the ignition coil, which increases primary coil current to ~5 amps, extending reliable spark energy to about 7,000 engine RPM.  Effectively, conventional ignition systems consume roughly 37% of the power used by HEI. 

Well, the method that conventional ignition systems use to limit coil primary voltage is to add resistance into the coil B+ lead - hence (referring now to the factory wiring diagram), the pink, 1.35 ohm resistance wire (ckt 3) that feeds power to the ignition coil. 

However, vehicle system voltage while cranking, prior to the engine actually starting, is effectively less than battery voltage (12.6 volts, versus 14.2 volts provided by the charging system once the engine is running).  To compensate for the decreased voltage available while cranking, the yellow wire (ckt 7A/7B) connected to "relay" terminal "R" of the starter solenoid bypasses ckt 3 and provides full battery voltage directly to the coil ...but only while cranking.  Once the engine starts, power transfer through the coil reverts through the resistance wire.

The problem that occurs when converting from conventional ignition to HEI is the resistance wire preexisting in the harness.  If the resistance wire is not replaced with a standard copper wire, HEI performance will be severely limited.

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Both terminals in the cap are 1/4" spade.  As Blazer explained, one is B+ in to power the ignition, the other is Tachometer signal out, when used.  The Tach terminal has a keying boss molded into the cap that prevents insertion of the B+ lead in the wrong position.  The factory style Series 56 connectors lock into the cap.  Typically the B+ connector is black, gray or natural, the Tach connector is most often brown and has a keying slot that matches the boss in the cap...



Occasionally, the B+ and Tach connectors are siamesed...



Factory style connectors use Series 56 female terminals.  To remove the terminals from the connectors use a flat blade pocket screwdriver or a terminal removal tool...



Thermal sleeve is not intended to wrap headers.  For that specific purpose use header wrap.

[Spool]

Wow, super informative. Thank you both, it allowed me to spot a few doors (youtube videos) to familiarize myself further on the matter.

So having HEI allows more reliable spark energy at a higher rpm than conventional in addition to not having any moving parts which also allows the elimination of arcing.
If I'm understanding this correctly, I no longer need a resistance going to the HEI distributor but a solid copper connection for full power from ckt3 which the distributor will rely
on after receiving it's initial power from my solenoid on my starter?

Further, the Y12guage wire currently plugged into the distributor cap is using the inside terminal closest to the firewall. The remaining terminal, would be for my tachometer? Which is currently not connected to anything explaining why my in-dash tachometer doesn't work?

Is this correct?

[Spool]

Hey BD,

May I ask where you buy your copper ring terminals?
I've been looking around and see that it's very common for anything smaller than 2 or 4 gauge to be mixed with tin.

I found this site:
http://www.mouser.com/Connectors/Terminals/_/N-5g5u?P=1z0z25hZ1z0xbvs

What is the benefit of 100% copper?

Thanks man.

[bd]

Plated copper, copper/tin alloy, plated brass - any of these will work just fine.  Alloyed copper improves ductility and hardness of the terminal while plating inhibits oxidation and improves solder adhesion.  I generally use "tinned" copper, closed barrel, brazed seam terminals.  Brazing makes the barrel of the terminal essentially a solid wall cylinder, which provides better clamping of the wire and better shape retention of the terminal barrel once crimped.  Mechanical crimping of the terminal onto the bare wire always precedes soldering.  Ofttimes, rather than buying bare terminals in quantity, I procure insulated terminals locally and simply strip off the insulating sleeve (image).  If you prefer to buy in greater quantities or need hard to find materials, look back through this thread for the link to retailers that I posted previously.

FYI - outside of special applications, avoid precious metal and high temperature terminals.  Although silver has a slight conductivity edge over copper, silver tarnishes quickly.  And, copper is a better conductor than gold at reduced cost.  High temperature terminals generally are plated with nickel and don't solder well.  Use ~0.030" diameter Sn60/Pb40, Sn63/Pb37, or Sn70/Pb30 rosin core solder for most electrical repair applications.  Silver bearing solder up to ~4% can be used to repair printed circuit boards where standing wave vibrations otherwise shear solder joints.  The silver imparts a subtle increase in tensile and shear strength to the joint.

[blazer74]

With HEI no need for the yellow starter wire to the distributor. Circuit 3 takes the place of the resistance wire with full voltage if you have removed/bypassed the resistance wire to circuit 3 and replaced with  a 12 gauge wire.

[bd]

If I'm understanding this correctly, I no longer need a resistance going to the HEI distributor but a solid copper connection for full power from ckt3 which the distributor will rely
on after receiving it's initial power from my solenoid on my starter?

Is this correct?

With HEI no need for the yellow starter wire to the distributor. Circuit 3 takes the place of the resistance wire with full voltage if you have removed/bypassed the resistance wire to circuit 3 and replaced with  a 12 gauge wire.

The following quote is from the Crankshaft Coalition website article, Hot rodding the HEI distributor:  "If converting to an HEI from a points-type distributor, the wire that was used to supply current to the point-type coil will be a resistor wire.  This is not needed or wanted for the HEI - it needs to be supplied with full system voltage without any resistor wire or ballast in the circuit for best performance.  Depending on the application this could mean rewiring or replacing the resistor wire for a 12-14 gauge supply wire.  Also, the wire from the starter solenoid “R” terminal can be eliminated."

The yellow wire (Ckt 7B) originally running between the starter "R" terminal and the HEI distributor "BAT" terminal won't cause any problem if left intact, BUT it is extraneous and totally unnecessary.  In effect, the only 12-volt circuit connection to the HEI distributor should be the 12-gauge wire coming directly from the ignition switch, through the firewall bulkhead connector Ckt 3 cavity circled in the following image, to the "BAT" (B+) terminal in the HEI distributor cap.  No other wires should connect into this B+ circuit!




The "TACH" terminal of the HEI distributor will connect to the input signal lead of a tachometer, if one exists.  Otherwise, it is unused.

Both the tachometer and B+ terminals of the HEI distributor are clearly labeled with "TACH" and "BAT" embossed onto the coil dust cover directly above the respective terminals...

[Spool]

Thanks guys.

BD.. Thanks for the tips on the plated and alloyed copper ring terminals.
I'll follow your lead and stick with local brazed ring terminals from autozone.
Thanks for the instruction on crimping the ring terminal before soldering also.
Why do you strip the insulation off?

I found this video online as well which I'll use as guidelines in soldering:
https://www.youtube.com/watch?v=6EiIDNEiB_U
https://www.youtube.com/watch?v=NTiz-tK5kK0

My solder gun/heat shrink/heat gun have all arrived, so I'll be finishing the job this week.
I'll undo the work of the following to solder it appropriately:
1)Starter Batt Terminal > 14gauge @ 6'' fusible link > 10g Red wire to Junction.
2)Solenoid Terminal > 12gauge > ckt6 in Bulkhead.
3)I think I'll leave the 2Gauge coming straight from the Car Battery, unless you guys think otherwise in soldering it?

Then I'll reconnect the remaining wires which I had taped off to the side.
1) 20gauge @ 8'' fusible link > 16g Black wire > SFE 4 AMP Fuse > ckt105 in Bulkhead.
2) Remove the 3-7 Splice connection entirely to replace the Resistive wire w/ a 12gauge straight to the distributor.

After I get through this job. I'll be figuring out everything that is going on in the junction box.

Thanks again guys. I'll post pictures when I'm done.

[bd]

Thanks for the instruction on crimping the ring terminal before soldering also.
Why do you strip the insulation off?     The insulation will melt from the heat of the soldering gun.  Shrink-seal the solder joints after soldering to protect the joints from corrosion and improve the appearance.

I found this video online as well which I'll use as guidelines in soldering:
https://www.youtube.com/watch?v=6EiIDNEiB_U
https://www.youtube.com/watch?v=NTiz-tK5kK0

My solder gun/heat shrink/heat gun have all arrived, so I'll be finishing the job this week.
I'll undo the work of the following to solder it appropriately:
1)Starter Batt Terminal > 14gauge @ 6'' fusible link > 10g Red wire to Junction.
2)Solenoid Terminal > 12gauge > ckt6 in Bulkhead.
3)I think I'll leave the 2 Gauge coming straight from the Car Battery, unless you guys think otherwise in soldering it?    Assuming you achieved a good mechanical crimp, solder the terminal to the cable and then shrink seal it.  To solder battery cable you will need a propane torch or equivalent, because the large cable will sink heat very rapidly - applying heat for too long from a small heat source such as a soldering gun may damage the cable insulation and never sufficiently melt the solder for good flow and suitable penetration.  Solder improves conductivity by increasing the surface area of contact between the conductors, but also seals joints to prevent the intrusion of moisture and corrosive salts.  Adhesive lined heat shrink hedges the bet against moisture intrusion.  To shrink-seal battery cables use triple-wall, adhesive lined, polyolefin heat shrink.

Then I'll reconnect the remaining wires which I had taped off to the side.
1) 20gauge @ 8'' fusible link > 16g Black wire > SFE 4 AMP Fuse > ckt105 in Bulkhead.
2) Remove the 3-7 Splice connection entirely to replace the Resistive wire w/ a 12gauge straight to the distributor.

After I get through this job. I'll be figuring out everything that is going on in the junction box.

Thanks again guys. I'll post pictures when I'm done.