Circuit 2 Wire

[Swiftness90]

The previous owner of my truck did a redneck job of putting a push button start in my truck. I have no power to the headlight switch and therefore no headlights, taillights or dash lights. When looking at my starter I have the red battery cable to the big stud on the starter and a 12 gauge wire running from the small stud on the solenoid up to the push button. Truck runs and drives fine, all my accessories (power windows, blower fan, radio, wipers) work fine. Am I missing the circuit 2 wire? If so, where does it plug in to from the starter?

EDIT: I have already replaced both the headlight and dimmer switch.

[bd]

What year/model truck? 

Verify power to the firewall junction block located above the engine near the brake booster and check the attached fusible link.  There are two additional fusible links connecting to the 3/8" battery cable stud on the starter solenoid.  If the links appear burned or stretch like rubber bands see "How to make a Fusible Link" in the Technical Pages of the Forum.

[Swiftness90]

What year/model truck? 

Verify power to the firewall junction block located above the engine near the brake booster and check the attached fusible link.  There are two additional fusible links connecting to the 3/8" battery cable stud on the starter solenoid.  If the links appear burned or stretch like rubber bands see "How to make a Fusible Link" in the Technical Pages of the Forum.

'82 K10. Is the junction block the thing with two metal studs near the top of the firewall? If so, there is no power there. Both fusible links on the starter seem to have been replaced with inline fuses by the previous owner.

[bd]

Is the junction block the thing with two metal studs near the top of the firewall? If so, there is no power there.

That's the firewall junction block.

Check the two fusible links at the starter.  The 12-gauge red wire that feeds power to the firewall junction block connects through one of the two fusible links to the 3/8" battery cable stud at the starter.  The wires from the starter solenoid run rearward around the back of the exhaust manifold then up the back of the engine to the firewall junction block and over to the firewall bulkhead connector.  Inspect the wires where they pass around the back of the exhaust manifold.  It is not uncommon for the wires to degrade from heat and/or burn on the exhaust.  Occasionally, the wiring will chafe bare and ground against the back of the cylinder head, or get pinched by the bellhousing during an engine swap or transmission R&I.  If a fuse link is damaged, make sure the wiring at the back of the engine is intact and not grounded.

[bd]

BTW - Fuses that substitute for fusible links are always suspect.  Fusible links are "slow blow" and able to handle common momentary power surges that will melt a fuse.  Additionally, fuse links are calibrated to the current capacity of the heavy-gauge feed wires they protect.  Fast-acting fuses that have been substituted for fuse links often "blow" so readily that an installer will increase the size of the fuse in an attempt to make them last.  Unfortunately, that compromises circuit protection - akin to placing a copper penny under a house fuse - and can result in catastrophic electrical fire (think, ash in the outline shape of the truck).

Since the PO modified the primary circuit protection, it might be prudent to determine if (s)he modified the feed wiring, as well.  Refer to the wiring diagram on page 1346 of the 1982 Service Manual for details of the factory feed wiring.  At some point, you will want to replace those 'substituted fuses' with appropriately sized fusible links.

[Swiftness90]

Ok so here's what I found out after some tinkering. Of the two studs on the junction box, the bigger one (driver's side) had two wires on it: the circuit 2 wire (right wire in pic) and one wire that goes to a fusible link and then splits into two wires (left in pic). I have 12v at the circuit 2 (right) wire, but no power at the one with the fusible link on it (left wire), as you can see the PO tried to fix the insulation on the fusible link with electrical tape, which has now come off showing bare wire. My assumption is this bare wire grounded against the firewall and blew the fusible link, could this assumption be correct? Also, where does the wire with the fusible link lead to?

[bd]

Clearly, the fuse link is trashed and needs to be replaced.  Did you look at the wiring diagram I linked?

One of the wire pair off the burned fusible link feeds the various light circuits (fuse block and headlamp switch) through the bulkhead connector, the other paired wire is the charge lead from the alternator.  The wire in your hand comes from the starter - it's the battery feed to the junction block. 

Rather than the fusible link being the cause of the problem, chances are greater that it just did its job and protected the vehicle from fire, because there was an alternator problem (shorted diodes or runaway output), or one of the two paired wires sharing the fusible link on the left abraded to ground.  You need to study the schematic and trace the Ckt 2 wiring.

The feed wire in your hand also could be the culprit due to insulation damage and grounding around the back of the motor as previously explained.

[Swiftness90]

Ok, I went out and did some work this morning before work. I replace the blown fusible link with one on each of the wires, cleaned up the connectors and now I have clean 12v power to the junction block. Still no lights, high beams, low beams and taillights all still don't work. I traced the one side of the split wire to the alternator where it connected to the alternator at the single stud, that connection was bad so I replaced it. Next, I found a 10ga red wire with a splice in it along the intake (see 1st pic) and plugs into the two wire plug on the alt, based on the length of this wire it seems suspect to me. Is there supposed to be another connection to/from this splice? Also along the intake I found a wire that leads to nowhere, it has a twist cap connector on it (second pic), any ideas where this is supposed to lead? I can't tell from the wiring diagram you linked.

[bd]

So the PO was electrically challenged, eh?  lol

The upper pic shows the "feedback" circuit (2G) connecting battery positive to the regulator #2 terminal.  The regulator senses system voltage via 2G to control alternator output.  Circuit 2G connects through a 'fusible link' to the 3/8" battery cable stud on the starter solenoid and is dedicated strictly to regulator function.  No other wires should splice together with 2G.

The lower pic is a puzzle.  Red is GM's standard color for the primary battery feed circuits that are generally protected by fusible links.  Follow the red wires rearward to see where they connect, and determine whether the PO reconfigured the factory wiring or just cut and respliced wires.

Looking more closely at the factory schematic, circuit 2J from the battery cable post on the starter passes through the bulkhead connector and changes number to 2F and 2G.  Circuit 2F directly feeds the headlamp circuit of the headlamp switch and circuit 2G feeds the tail/courtesy light and horn fuses in the fuse block. 

Sometimes power is interrupted through the bulkhead connector due to poor connection.  See if you have power on the red 2J and 2F/2G wires on both sides of the bulkhead connector.

[Swiftness90]

So should I run both the 2G wires to the 3/8 stud on the starter in order for my alternator to accurately regulate itself?

[hatzie]

So the PO was electrically challenged, eh?  lol

The upper pic shows the "feedback" circuit (2G) connecting battery positive to the regulator #2 terminal.  The regulator senses system voltage via 2G to control alternator output.  Circuit 2G connects through a 'fusible link' to the 3/8" battery cable stud on the starter solenoid and is dedicated strictly to regulator function.  No other wires should splice together with 2G.

Not correct.  See the attached engine compartment wiring diagram exported from the uncompressed TIFF files...  It should be a bit more readable than the compressed service manual scan.
Engine compartment Wire 2G (Alternator feedback) shares the 1mm˛ (18AWG) fusible link 2H, at the starter motor, with circuit Engine compartment side Lighting power Wire 2J. 
I am not sure why they did this.  I doubt it would cause problems to replace Fusible link 2H with two fusible links.

Be careful following the GM schematics too.  The letter suffixes get recycled on the Cab side of the firewall (noted as "front of dash"). 
What this means is... Engine compartment Wire 2F (the 2C alternator BATT & 2E Cab-power fusible link at the junction stud) is not the same wire or gauge or... as Cab side Wire 2F (Headlamp switch power).
Click to enlarge
 

[hatzie]

Ok so here's what I found out after some tinkering. Of the two studs on the junction box, the bigger one (driver's side) had two wires on it: the circuit 2 wire (right wire in pic) and one wire that goes to a fusible link and then splits into two wires (left in pic). I have 12v at the circuit 2 (right) wire, but no power at the one with the fusible link on it (left wire), as you can see the PO tried to fix the insulation on the fusible link with electrical tape, which has now come off showing bare wire. My assumption is this bare wire grounded against the firewall and blew the fusible link, could this assumption be correct? Also, where does the wire with the fusible link lead to?

That should be 1mm˛ (18AWG) Fusible link 2F. If the insulation burned off it's in need of replacement.

[Swiftness90]

http://

That should be 1mm˛ (18AWG) Fusible link 2F. If the insulation burned off it's in need of replacement.

Ok, I replaced it with a fusible link on each wire. I'm going out to test power at the headlight switch. If I don't have power there, where should I be looking next?

[hatzie]

Two questions...
Does engine compartment red wire, 2G in the diagram snippet I posted, have continuity to the 3/8" starter ring terminal?
Do the horn and parking lights work?


From orbit on my Android.

[bd]

...The upper pic shows the "feedback" circuit (2G) connecting battery positive to the regulator #2 terminal.  The regulator senses system voltage via 2G to control alternator output.  Circuit 2G connects through a 'fusible link' to the 3/8" battery cable stud on the starter solenoid and is dedicated strictly to regulator function.  No other wires should splice together with 2G.

Not correct.  ...Engine compartment Wire 2G (Alternator feedback) shares the 1mm˛ (18AWG) fusible link 2H, at the starter motor, with circuit Engine compartment side Lighting power Wire 2J.
I am not sure why they did this....

Semantics.

2G and 2J share a common source (battery) through the 2H fusible link at the starter.  But, 2G does not connect to any circuit except the regulator.

The headlamps and lighting, collectively, are a high-current (and very visible) circuit.  The headlamps generally won't be used unless the engine is running and the alternator is charging.  With the headlamps on, there's a slight voltage drop across the 2H fusible link.  Since regulator feedback current is negligible, it doesn't impinge on the headlamp circuit, hence doesn't increase voltage drop across the link.  Having the regulator feedback circuit monitor voltage on the headlamp feed helps to eliminate lamp flare as alternator burden and output fluctuate with engine RPM.  So, sharing the link was just a convenient point of circuit connection while minimizing customer complaints.

Incidentally, 1mm² fusible link is 16 AWG, not 18 AWG.  There's a handy chart at the bottom of page 1337 in the 1982 Service Manual that correlates the metric and English wire size standards. 

Ok, I replaced it with a fusible link on each wire....

To maintain safe circuit protection against electrical fire while not introducing excessive resistance, it is very important to use the correct size fusible link.  With regard to automotive wiring, the standard rule is to use a 6" length of fusible link that is four wire gauges (AWG) numerically larger than the wiring it protects.  In practice, use 6" of 16 AWG (1mm²) fusible link to protect 12 AWG (3mm²) wire; use 6" of 18 AWG (0.8mm²) link to protect 14 AWG (2mm²) wire; and so on.

So, you should have used 6" of 16 AWG (1mm²) fuse link on each wire - or, 6" of 16 AWG fuse link to the pair as originally constructed.  Either method will work.

All these numbers are giving me a headache!   

...I'm going out to test power at the headlight switch.  If I don't have power there, where should I be looking next?

If you already have the instrument cluster or headlamp switch out, the simple answer is check for power on the red 2F wire at the headlamp switch.  If it's dead, probe the Tail/Courtesy fuse in the fuse block.  If it's dead, probe the 2F/2G wire pair as they exit the bulkhead connector under the dash.  If they're dead, probe the 2F wire where it enters the bulkhead connector in the engine compartment.  Work your way back toward the battery cable stud on the starter.

On the other hand, if you haven't already taken the instrument cluster or headlamp switch out, this will establish whether you have power through the fusible link and into the cab with less work....

Two questions...
Does engine compartment red wire, 2G in the diagram snippet I posted, have continuity to the 3/8" starter ring terminal?
Do the horn and parking lights work?