Author Topic: Headlight switch wiring identification question  (Read 32762 times)

Offline ThunderLizard

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Headlight switch wiring identification question
« on: August 28, 2015, 08:30:49 AM »
HELLO!
New to this site, and new to this truck.  I hope you guys can help!  I was happy I found this forum since I need all the help I can get.

Background:
1985 Chevy c30 350v8, flat/dump bed.  This truck belonged to my dad.  It was abandoned in a field for several years.  I'm trying to turn it into a functional, reliable, towing, hauling, farm truck.  No show truck here.

Issue:
Trying to get the headlights working.  Replaced a lot of elec components so far (battery, battery cables, ground wires, 30A circuit breaker) and the lights themselves.  I've got the running lights/blinkers and taillights working now.  This is the "2 headlight" setup where the brights and dim headlights are in one housing. 

I found a lot of incorrect wiring diagrams on the internet.  I also found some "custom"  ??? wiring under the dash.  I'm getting that all sorted.

My question for you fine fellows is this:
Which wires are which attached to the headlight switch?

White (above Red) -  ?, maybe dome lights?
Red (larger) -  Power in?
Green - ?
White (next to Green)  -  ?, maybe top-cab running lights?
Purple - ?
Yellow - ?
Orange (2X) - ?

(Side question: how do you get the knob off this switch?  Some trick?)

Offline bd

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Re: Headlight switch wiring identification question
« Reply #1 on: August 28, 2015, 11:27:40 AM »
Welcome to the site!

Linked is the factory 1985 Wiring Manual (see pages 9 & 10), courtesy of hatzie.

The headlamp switch knob is released by depressing a small metal button on the backside of the switch housing (see image).
  • white (offset but adjacent to red) = controlled ground circuit from the dome and courtesy lamps (full CCW rotation of the headlamp switch knob grounds this wire to illuminate the interior lights).

  • red = main B+ feed from the fusible link (hot at all times) - powers the headlamps only.  The red wire feeds power to the non-serviceable circuit breaker integral with the headlamp switch.

  • green = dimmer controlled dash lamp circuit that routes power to the redundant 5-amp "INST LPS" fuse in the fuse block.  Rotating the headlamp switch knob varies the voltage on the green wire and instrument lamps fuse.

    Power into the instrument lamps dimmer comes from the 20-amp "T/L CTSY" lamps fuse via one of the two orange wires (details below).

    Power out of the instrument lamps fuse routes to the three "LPS" sockets located directly above the fuse and to the dash lamps via a gray wire.

  • white (adjacent to green) = this wire position is equivalent to brown and may be used to power the cab roof lamps if you have that option.

  • purple = this is actually "brown" and feeds all of the tail, park, marker and license plate lamps.

  • yellow = feed to the headlamp dimmer switch.  Red (B+) is switched by the headlamp switch and then power is routed directly to the dimmer switch for high/low beam selection.

  • orange (x2) = one is power from the 20-amp "T/L CTSY" fuse in the fuse block (hot at all times).  The remaining orange wire feeds unswitched B+ directly to the optional courtesy lamp mounted under the dash.

Edit:  In haste, I missed your attached image the first go 'round...
« Last Edit: August 28, 2015, 09:43:20 PM by bd »
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 ThunderLizard

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Re: Headlight switch wiring identification question
« Reply #2 on: August 31, 2015, 07:01:43 AM »
 ;D
HOLY HECK!  This is exactly the information I needed.  I didn't have much time this weekend, but I did check and found that I have power to all of these wires (when switch is fully on) EXCEPT the yellow wire, which goes up to the Bright/Dim switch.  I'm going to order a new headlight switch and replace.  I think this will solve this issue, but I'm also open to other suggestions.

Again, bd, thank you so much for taking the time to answer this and provide the wiring manual.  Many hours were wasted looking at incorrect wiring diagrams and trying to see wire routing through 30 years of gunk and grease.

I'll post again on this thread with the final outcome after I've replaced the light switch.

Offline bd

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Re: Headlight switch wiring identification question
« Reply #3 on: August 31, 2015, 08:43:33 AM »
You're welcome.  Smooth sailing!
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 ThunderLizard

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Re: Headlight switch wiring identification question
« Reply #4 on: September 08, 2015, 03:14:26 PM »
So, I had a few minutes to work on the truck this weekend. (I spent most of my free time burying 250 ft of electrical feed to my new chicken coop. Woo Hoo!)

Anyway, I replaced the headlight switch with a new one from Rock Auto [ACDELCO D6252D {#19106995} Professional].
After replacement I had power to the yellow wire, which goes to the headlight dimmer switch.  The yellow wire was hot at the headlight switch and at the dimmer switch.
The light green and tan wires coming out of the headlight dimmer switch are NOT HOT with all lights on.
Is it possible that I had a bad headlight switch AND a bad dimmer switch?  Seems like that is what I'm looking at here....

I just ordered a new dimmer switch [ACDELCO D832 {#26019661} GM Original Equipment] and Wiring connector [ACDELCO PT1994 {#88860549} Professional Switch Connector 3 Term. Female; Black; w/ Locking Tabs].  I'll change out this switch next weekend and hopefully the new headlights will be so bright and glorious that they will blind all that dare look into them.  ;D

Of course, I might still find that the headlights won't come on and I'll have to keep trouble shooting down the line.

A quick question: some sources talk about a "fusible link" on the headlights.  I've been all up and down the wiring under the hood and under the dash and I don't see anything that looks to be a fusible link.  I do have a 30 amp circuit breaker on the positive lead from the battery, but I have yet to see anything resembling a fusible link.  If I did have a fusible link, where would it be?  Am I missing it or is it likely not even there?

Offline bd

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Re: Headlight switch wiring identification question
« Reply #5 on: September 08, 2015, 03:49:03 PM »
With a properly functioning and connected dimmer switch, when the yellow feed wire is hot, EITHER the tan (low beam) wire OR the green (high beam) wire also will be hot.

Factory installed fusible links are the primary circuit protection for the vehicle.  They protect the 10- or 12-gauge red wires connected to the starter solenoid 3/8" battery cable lug and the double-stud firewall junction block located above the back of the engine.  Generally, there are three, occasionally four, fusible links - typically, two at the starter and one or two at the junction block.

For the headlamps to shine at their brightest, they should be reconfigured with relays and heavier gauge wire.  The factory configuration was under-engineered.
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 ThunderLizard

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Re: Headlight switch wiring identification question
« Reply #6 on: September 09, 2015, 09:11:05 AM »
bd - you da' man!

I'm now researching relays, and I'm fairly certain this what I'm going to install.  The internet seems to agree with your assessment: that the original design was not great and that a relay system is an improvement.  After the dimmer switch is replaced, I may as well install relays and new wires.  To me, this just make sense to not only eliminate old, possibly rat-chewed wires, but to upgrade the entire headlight system.  I've come this far, I may as well go all the way, right?

I'll check back in after I've completed the work (or when it goes bad and I need more help  ;D )

Thanks again!!

Offline ThunderLizard

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Re: Headlight switch wiring identification question
« Reply #7 on: September 10, 2015, 12:26:50 PM »
I'm trying to find a source for relays, and I'm not having much luck.  Where is the best place to start and what sort of relays should I get?

Offline bd

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Re: Headlight switch wiring identification question
« Reply #8 on: September 10, 2015, 08:49:15 PM »
Instead of reinventing a complete harness, use the existing factory wiring to control a plug-n-play, heavy-duty, relay lamp kit that powers the headlamps directly from the battery.  Easy, fast, reliable, and relatively inexpensive....

Another thing you can do for brighter headlights is to put in a headlight relay.  On my '78 K-10 I used a "H4 9003 P43t relay harness" from Autolumination (scroll about 1/4 of the way down the page).  This does not require any wiring changes, as it has a connector that mimics the back end of the stock headlight.  The existing truck wiring controls the relay, and the relay drives the bulbs right off the battery.  For a double stack, you may need two of these, or there may be an alternate relay setup.  The point is to get the wiring from the battery to the bulbs as short as possible, with as few connections as possible, and get all the stock wiring and the headlight switch out of the power circuit, and just use that stuff to control the relay.

They have headlights and baskets and bulbs as well, but I was unimpressed with [them].

If the factory wiring is in dubious condition and needs to be replaced, or if you just like to tinker, use two Bosch SPDT or SPST 5-pin relays, a couple of matching relay sockets, a pair of headlamp sockets, and 12-gauge green, tan and black wire.  The Bosch style relays have been around forever, are proven to work well, and are readily available:  Del City, Terminal Supply Co, The Electrical Depot, Summit Racing, NAPA, etc.  Don't forget the selection of various terminals, heat shrink, 60/40 solder, tape, loom, wire strippers, crimpers, soldering iron, etc.  Building your own harness gives you more control over the design, but generally is much more expensive and complex. 
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 ThunderLizard

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Re: Headlight switch wiring identification question
« Reply #9 on: September 22, 2015, 06:57:15 PM »
OH YEAH, all the exterior lights are now working... probably the 1st time in 20+ years.  I wanted to pop back here, give updates, and especially offer thanks to bd.

So, I ended up ordering a relay harness from Autolumination.  I worked with Chris Bacon, who was knowledgeable and helpful.  I had him affix H6054 connectors to the relay assembly.  There was an extra cost for this, but worth it in my opinion.  I ordered these on Wednesday and had them in my hands Saturday morning.  Not bad for $5 shipping.  Excellent initial quality, all wires were exactly the proper length so no modifications of the relay harness was needed.  Literally plug-and-play. I ended up spray painting the front of the relay box: a little too much Chinese printing for my ol' American truck. 

I replaced the dimmer switch, was bad.  I used Rock Auto ACDELCO D832 ($16).  This was a $#@% to change, just because the top retaining screw is nearly inaccessible.  I wonder if it would have been easier to drop the column.  Anyway, I used a small star washer to hold the screw in place so I could align it and that worked pretty well. 

I had a couple of other minor wiring issues with running lights around the dump bed, but those were easy to fix with standard crimps, splicers, and connectors.

The end result: ALL EXTERIOR LIGHTS WORKING.  Quite satisfying to finally have this whipped.

Thanks again bd!  I couldn't have done it without your help.  If I ever meet you in the real world, beers on me.
Next: Fuel tanks, gauge, and tank switching valve.

Offline bd

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Re: Headlight switch wiring identification question
« Reply #10 on: September 22, 2015, 07:51:58 PM »
WHAT ! ? ! ? !  :o     This isn't the real world ! ? ? !   ???



Glad you got 'er done!    8)



PS - It is far easier to drop the column...  A/C crossover duct, four screws, 2 nuts and the gear selector cable....    ;)

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 Spool

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Re: Headlight switch wiring identification question
« Reply #11 on: January 19, 2021, 07:45:31 AM »
Hey BD,

Would this wiring chart you typed be fitting for a 73 C20, or would it be different?

Welcome to the site!

Linked is the factory 1985 Wiring Manual (see pages 9 & 10), courtesy of hatzie.

The headlamp switch knob is released by depressing a small metal button on the backside of the switch housing (see image).
  • white (offset but adjacent to red) = controlled ground circuit from the dome and courtesy lamps (full CCW rotation of the headlamp switch knob grounds this wire to illuminate the interior lights).

  • red = main B+ feed from the fusible link (hot at all times) - powers the headlamps only.  The red wire feeds power to the non-serviceable circuit breaker integral with the headlamp switch.

  • green = dimmer controlled dash lamp circuit that routes power to the redundant 5-amp "INST LPS" fuse in the fuse block.  Rotating the headlamp switch knob varies the voltage on the green wire and instrument lamps fuse.

    Power into the instrument lamps dimmer comes from the 20-amp "T/L CTSY" lamps fuse via one of the two orange wires (details below).

    Power out of the instrument lamps fuse routes to the three "LPS" sockets located directly above the fuse and to the dash lamps via a gray wire.

  • white (adjacent to green) = this wire position is equivalent to brown and may be used to power the cab roof lamps if you have that option.

  • purple = this is actually "brown" and feeds all of the tail, park, marker and license plate lamps.

  • yellow = feed to the headlamp dimmer switch.  Red (B+) is switched by the headlamp switch and then power is routed directly to the dimmer switch for high/low beam selection.

  • orange (x2) = one is power from the 20-amp "T/L CTSY" fuse in the fuse block (hot at all times).  The remaining orange wire feeds unswitched B+ directly to the optional courtesy lamp mounted under the dash.

Edit:  In haste, I missed your attached image the first go 'round...

Offline bd

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Re: Headlight switch wiring identification question
« Reply #12 on: January 19, 2021, 07:56:59 AM »
Diagnosing dash instrument lights should pretty apply to all model years of our trucks.  For the specific year wiring diagram, refer to the factory wiring diagram in the Technical Pages.
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)