Author Topic: Accessory Power Issues  (Read 251 times)

Offline lilkiduno

  • Newbie
  • Posts: 26
  • Newbie
Accessory Power Issues
« on: June 10, 2019, 12:22:53 AM »
1984 C10 305 with gauges.

Okay guys,

I am attempting to hunt down an issue my truck had began doing. I was driving home and all a sudden my Choke light illuminates. I knew it was something that needed addressed, however I had other things going on and it got back put on the back burner. Now I am trying to track down the issue, now that it's not raining like crazy. After the choke light I noticed the Volts gauge was reading too high, Higher than was I thought was normal, just below the 15 mark, I thoughtto myself the alternator puts out 14.6 if i remember correctly, no big deal. Turns out I went to step on the gas and my radio dies, look at the volt meter again and it's over the 15 volt reading, under acceleration it increases, got over 15 volts and it shut my radio off, bring it back to idle and it gets below 15 volts the radio come back on. Okay, that had to be alternator, well take it to get tested, the machine at oreilly's reads bad on all the tests, resistors regulator and the third test, can't remember what, all failed. Purchase a new alternator and install, the voltage on the gauge appears correct. Choke light is still on, I have no power windows, no blower motor. I don't know if these are connected, but when I try to use these accessories (windows and blower) the choke light illuminates brighter. Checked fuses at the choke and gauges, both okay, will check fuses for windows and blower tomorrow. I am looking at the wiring diagrams lost in lines and am hoping someone may have some insite. I know I need to check the fuses tomorrow and I will. Just with the summer weather approcing power windows are becoming a must and any help would be appreciated.

Oil pressure gauge dosen't work, replaced the oil pressure switch because I read it could be out.

Offline 75gmck25

  • Frequent Member
  • **
  • Posts: 365
  • 1975 GMC K25 Camper Special, 350/TH350/NP203
Re: Accessory Power Issues
« Reply #1 on: June 10, 2019, 05:33:49 AM »
Its most likely that you have a ground wire broken or loose, and those circuits are finding a ground path when you turn on other accessories.

Grounds to check:
- Large ground wire from battery to alternator bracket; use star washer and make sure its a good solid connection
- Small ground wire from battery terminal to firewall
- Ground on each side of firewall from the headlight wiring
- Ground from engine to firewall.  Often connected to a bolt on the back of the engine on passenger side, or a bolt on the valve cover.
- Ground from frame to engine, usually down low on the passenger side near the fuel pump
- Instrument panel ground up under the dash. Might be connected to a post on the emergency brake, or on newer trucks to a ground bus up under the dash
- Large ground wire in back of the truck wiring about in the middle of the bumper, and a smaller ground wire for each taillight.

There may be others for specific accessories.  For example, the choke sensor (on the oil pressure switch?) may have a ground on one side that is now disconnected or not making a good connection to the engine.


Offline bd

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 5288
Re: Accessory Power Issues
« Reply #2 on: June 10, 2019, 04:38:45 PM »
As suggested by 75gmck25, verifying all grounds is a prudent starting point. 

Avoid star washers for ground connections and especially for battery cable connections.  Star washers can allow moisture intrusion to the connections, which exacerbates corrosion.  In addition, they decrease the surface area of direct metal contact.  Rather, burnish metal at the attachment site until it is bare, clean and shiny.  Make sure that ring terminals are properly sized to the bolt used to attach them.  Then liberally coat the terminal and attachment point with antioxidant during assembly. 

Never connect the engine-to-firewall ground strap to a valve cover bolt.  Attaching to a valve cover bolt will invite grounding trouble for all cab appliances.  Instead, attach the ground strap under a 3/8" bolt at the back of the passenger side cylinder head.

The Choke light grounds through the choke thermostat heating element.  See the technical article, GM electric choke operation for Q-jet carbs for details on function.

The following inventory of 1973 - 1987 (91) GM truck grounds is excerpted from the technical article, Vehicle Ground:

Whether you are experiencing electrical problems or refurbishing the vehicle, take an inventory of all of the vehicle grounds and service them appropriately (disassemble and clean connections to shiny bare metal, followed by liberally coating terminals and connections with moisture rejecting antioxidant paste).  Upon inspection you should discover the following vehicle grounds; recommended wire sizes are listed for any ground paths that need to be fabricated and installed:
  • battery-to-engine block or alternator bracket (2 gauge)    this is the primary high-current ground path (>150 amperes) for the engine and cab, supporting the full burden of the starter cranking current, charging system current and cabin electrical appliance current.  DO NOT attach the battery ground cable to an intake manifold bolt or stud!

  • battery-to-right (passenger side) frame rail (10 gauge)    this ground path is crucial as the primary extension of the main vehicle ground to the rear of the vehicle

  • battery-to-radiator support (10 gauge)    this is the primary ground path in support of all of the forward running lamps, forward turn signals, headlamps, and horn(s)

  • back of right cylinder head-to-cabin firewall (5/16" braided strap or 8 gauge)    this primary ground path ensures the cabin is adequately grounded in support of all cabin mounted interior and exterior electrical appliances

  • dash lighting and interior appliances-to-cabin left kick panel sheet metal (various, but typically 18 and 16 gauge)    this shared grounding point, common to nearly all of the electrical appliances inside the cab, interior lighting and instrument panel, is crucial to preventing the occurrence of floating grounds and associated electrical ghosts.

  • rear lamps-to-bed (16 gauge)    ensures the rear lamps are suitably grounded; alternatively, ground the rear lamps directly to the right frame rail

  • bed-to-right frame rail (14 gauge)    ensures the bed is suitably grounded in support of the rear lamps and other appliances grounded to the bed

  • cabin firewall-to-engine compartment hood (1/4" braided strap preferred for superior flexibility, otherwise 12 gauge, suitably located with sufficient length to allow opening and closing of the hood without catching, excessive flexing or stretching of the wire)    (optional yet highly recommended) helps manage radio "bzzzzzzz" and provides a stable ground for an optional hood mounted engine compartment lamp
Additional primary ground connections are okay.  If any of the recommended ground connections are missing, fabricate and install them!  If damaged, repair or replace them!

Other areas to check are the fusible links and harness connections at the starter and firewall junction block.  Loose connections or compromised fusible links can cause "mysterious symptoms."

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)