No low beams, no running, high beams weak, backfeed right blinker indicator

[arby87]

So now I get to mess with the rat's nest of wiring under my dash, as I need to get my headlights working properly.

87 V10 Custom Deluxe, craigslist frankentruck, 350/th400, NP 208, 4.10s, 4" lift, dual headlamps (not quad).

I do have all my blinkers currently working, just the stalk switch doesn't want keep the left turn signal on for very long (clicks off fairly easily), which I attribute to a worn stalk switch. My main issues are listed below:

- First pull on the headlamp switch I get nothing- no running lights (think most are blown out, will have to get new ones) but the radio powers on (crappy aftermarket unit).

- Second position of the headlamp switch is no change.

- Third position (high beams) gets the headlamps to light up, but are dull and way out of alignment. One is a new Sylvania which is the brightest, the driver side is an older halogen (don't remember the brand) that is a noticeably dimmer. Bought a replacement for that, just not swapped in yet. This position causes the right blinker indicator on the dash to light up- pretty brightly I might add. Before I had cleaned the grounds I believe both indicator lights would light up in this position, but as of last night only the right one does now. 

- Rheostat function of the headlight switch to control dash light brightness works.

- Full turn click to turn on the cab light works. 

Work I have done so far-

- Cleaned the engine bay grounds. B- terminal, B- to radiator support, radiator support to driver side light assembly, B- to alternator, B- to frame.
- Sprayed out headlamp connectors with WD-40 and plugged/unplugged several times as well as taking some sandpaper to the headlamp spade terminals.
- Verified ground connectivity to associated ground points via ohmmeter between those points and B- after cleaning.
- Probed headlight connector (three prong) with test lamp when the switch is set to low beam, no result (expecting no power to switch at this point).

I have bought a new headlight switch just in case, but that seems to be rarely the problem. I have glanced at my fuse box, and seen some concerning items (like a spade connector plugged directly into a fuse slot- will get pics soon). I have a distinct feeling the P.O. probably wired the stereo into the headlamp switch instead running a new circuit, and the original owner had done quite a bit of his own splicing for a trailer that is half removed.

I also have an intermittent Service Engine Soon light issue- but when I took it in to read the code, the scanner would not power on with the truck in the "Run" position. Tech told me to fix getting power to the diagnostic port and then try again. The SES seems related to an occasional miss I get from time to time, but I am thinking that might get fixed when I do a tune up- especially since a couple of the spark plug wires are lying directly on the exhaust manifold.

Pics to follow. Think my first step is to pull the headlight switch and check all it's connections. Thinking I will just yank the stereo and associated wiring for now- speakers are blown any how and I want to make sure all the wiring is legitimate before attempting a new unit.     

[bd]

Headlamp switch has three positions: 1) pushed in > OFF, 2) middle detent > running lamps only, and 3) all the way out > running lamps plus headlamps.  High beam versus low beam is controlled by the dimmer switch.

Begin by replacing any bulbs that display broken or melted filaments or measure open as indicated by an ohmmeter.  There are two B+ feeds into the headlamp switch - one B+ feed (for running lamps and dash lamps) is protected by the 20-amp TAIL/CTSY fuse in the fuse box, the other B+ feed (for headlamps) is protected by one of the fusible links in the engine compartment.  The dash lamps are redundantly protected by a 5-amp INST LPS fuse in the fuse box.

The fact that the dash lamps illuminate is evidence enough that the 20-amp TAIL/CTSY fuse and the 5-amp INST LPS fuse are both functional.



Color coded to the factory wiring (and image), headlamp switch connections are:

RED - B+ feed from fusible link into headlamp switch for headlamps only

WHITE - Courtesy/dome lamp switched ground

YELLOW - Power out to headlamp dimmer switch

GREEN - Rheostat controlled power out to INST LPS fuse and dash lamps

BROWN - Power out to running & tail lamps

ORANGE - B+ feed from TAIL/CTSY fuse into headlamp switch for running, tail & dash lamps

After replacing the necessary bulbs, recheck the grounds for all of the front lamps on both sides - right and left - headlamps and park/turn lamps.  Use a voltmeter to measure voltage delivered to the headlamps with the headlamps plugged in and switched ON - both high beam and low beam.  Then measure the voltage drop between battery B- and the ground wires for the headlamps at the headlamp connectors with the headlamps switched ON.  Repeat the voltage measurements at the dimmer switch connector yellow, light green (high beam) and tan (low beam) wires.


Edit:  refer to the 1987 Wiring Manual Section 2 Page 1 (forward lamp wiring) and Section 7 Pages 1 & 2 (dimmer switch & headlamp switch wiring, respectively) for additional details.

[arby87]

Thanks bd- will be looking into those checks as soon as I can get away from my small children. Seems neither the twins want to sleep more than 3 hours at a time these nights and is driving their mother and I crazy.

Here are some pics, and a little bit of an update. I did have the left indicator lamp working for a little while, but now it has stopped working. I am pretty sure if I go back and re-check it's grounds it will work and will have the dash indicator light glow like the right one does when headlights are on. I do have rear running lights working, but not until the headlight switch is pulled completely out (third position). I still get nothing except dash lights and radio on the first pull.

you say high beams are controlled by the rheostat function of the headlight switch and only when pulled all the way out? I was under the impression running lights and low beams on first pull, then highs on second pull.....

EDIT: Is it feasible/better to change out to a relay setup for the headlamps instead of running all that load through the headlight switch?

[bd]

It sounds like the headlamp switch is faulty and/or the wiring has been altered.  Check the wire connections to the headlamp switch using the color codes previously provided.  Ensuring good grounds and viable lamps are a good beginning.

The dash instrument lamps are controlled by a "dimmer rheostat"  that is integral with the headlamp switch - rotate the headlamp switch knob clockwise to dim instrument lighting, counter-clockwise (CCW) to brighten.  Full CCW rotation of the headlamp switch knob, to its detent position, also turns on the cabin dome/courtesy lights. 

Headlamp switch operation:  Pushed In = off, Pulled Out to Middle Position = park/tail/instrument lamps, Pulled All The Way Out = park/tail/instrument/headlamps.  High beam and low beam are controlled by a separate, steering column mounted "headlamp dimmer switch"  that is operated by the turn signal lever.  Pull the lever toward you to "click" then release to switch between high beam and low beam, alternately.

Light-duty truck headlamp switches of the 73-87 (91) vintage are a notably weak point in GM's engineering.  They generally function, but right at the edge of their current handling capacity.  You will gain luminosity by converting to relay operated headlamps and heavier gauge wire.  Plug-N-Play relay conversion kits are available commercially, or you can fabricate your own.  Commercial kits are often the less costly approach if you don't already possess the materials and tools needed for fabrication.