Author Topic: No clue where to look...  (Read 123 times)

Offline jpatters13

  • Newbie
  • Posts: 60
    • 74' Chevy Truck Project
No clue where to look...
« on: July 09, 2018, 08:44:17 PM »
I have a 1974 C10 2WD short bed stepside.  Ground up, frame off restoration one nut and bolt at a time, just me and my son.  Three years later I am ust a few weekends from being finished but have a HUGE electrical issue.  I replaced the stock glass tube fuse harness with a GM EZ Wiring harness.  I have connected every wire and ground exactly as it should be...at least that's what I thought.  Here's the issue, I have power to the guages, and headlights, but no power to anything else.  No dash lights, running lights, turn signals, brake lights, hazard emergency flashers...NADA.  The truck runs and drives and fires over on the first try.  I am at a loss as to where to begin chasing down the gap in the system.  Any advice or educated steps as to where to begin would be greatly appreciated.
84 Silverado K10
74 Custom Deluxe C10

Offline bd

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 4790
Re: No clue where to look...
« Reply #1 on: July 09, 2018, 10:19:05 PM »
So, in fact, you do have at least partial ignition power or the engine wouldn't crank and start.  Being unfamiliar with the specific wiring harness you mentioned I can provide only generalizations on what to investigate.  Begin by physically removing and carefully inspecting every fuse for a cracked or melted element.  Verify that both flashers are installed in the fuse box.  The headlamp switch requires two sources of B+ power to function: one B+ source powers the headlamps and the other B+ source powers the running lamps.  See Diagnosing dash instrument lights for details.  Check that the turn signal switch is properly plugged into the dash harness.

Using an incandescent test light rather than a voltmeter, verify that the fusible links are properly connected to B+ at the starter solenoid 3/8" battery cable stud.  Probe for power at the firewall junction block located above the left valve cover.  Verify that B+ is arriving at the firewall bulkhead connector via the 12- or 10-gauge red wires as well as through the bulkhead connector into the cab.  Any 12-gauge red wires connecting directly to the fuse box should provide constant battery power into the box.  Confirm that no terminals have been dislodged from the fuse box and pushed out the back.  Verify that B+ is arriving at the ignition switch on both of the two 12-gauge red wires and that the wiring harness plugs are properly mated to the ignition switch.  One 12-gauge orange wire returns to the fuse box from the ignition switch and should be Ign+ only in the RUN position of the ignition switch.  The pink wire bearing a black stripe coming from the ignition switch will be Ign+ only in the RUN and CRANK positions of the switch.  The brown wire coming from the ignition switch will be Acc+ only in the ACCESSORY and RUN positions of the switch.

These steps should at least get you started if not lead you directly to discovery of the problem.
Rich
It's difficult to know just how much you don't know, until you know it....
In other words... if people learn by making mistakes, by now I should know just about everything!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline jpatters13

  • Newbie
  • Posts: 60
    • 74' Chevy Truck Project
Re: No clue where to look...
« Reply #2 on: July 10, 2018, 05:37:23 AM »
Thanks.  I'll give it a shot.  I no longer have a bulkhead power collector at the firewall inside the engine compartment as this harness provided all individual wires needed to run the vehicle.  The harness is brand new and there appear to be no burned wires or fuses and everything is tightly plugged into the fuse block.  I am thinking that some sort of accessory power is not connected properly.  Also, If I bypass the headlight switch and provide power directly to the running lights at the switch, they all illuminate.  That would lead me to believe the switch was bad, but I had two headlight multi-function switches and they both showed the same glitch.  I bought a new switch and still the same issue occurs.  I'll keep digging.  If any other ideas come to mind I am all ears.  Thanks again.
84 Silverado K10
74 Custom Deluxe C10

Offline jpatters13

  • Newbie
  • Posts: 60
    • 74' Chevy Truck Project
Re: No clue where to look...
« Reply #3 on: July 11, 2018, 06:07:58 PM »
Problem solved! First the brand new fuse panel had a blown Hazard fuse.  Second, the multi-function headlight switch requires two power sources.  One direct wire for the headlights and a second, fused connection, for power to the remaining lights.  The new fuse panel from EZ wiring didn't have a second, fused power source for the other lights.  I took the "trunk light" wire (not needed for my truck) and supplied the power from there.  Everything works!!

Thanks for the advice.
84 Silverado K10
74 Custom Deluxe C10