Light issues, parks and turn signals

[1967KaiserM715]

So I am trying to sort out my truck, 1985 GMC K1500, with the single Headlight style system, Diesel. Headlights seem to work, forgot to check high beams; also have the rear harness disconnected, the harness that mounts to the truck bed appears to have a short somewhere between the brakes and parks/turns; I have not used my power probe to check the actual rear harness that runs from the fuse box yet, it is on my list to do.

My symptoms, no drivers/left side park lamps, passenger/right side lamps do work, no turn signals, hazards do work-I switched relays, everything remained the same. I have nothing on right side turn signals-no indication of wanting to flash, no dash light. Left turn is a little more fun, low coolant light flashes, seatbelt and buzzer flash, glow-plugs will flash, and dash left turn will flash. the left side dash turn will also stay lit, although it does it randomly. Lights still don't work.

Drivers bulbs are OK, but I will be checking again to make sure that the issue I'm having hasn't killed them. Dash lights appear to work fine as long as the rear body harness is disconnected-kept blowing a fuse, T/L CTSY, but the 5amp INSTR LPS circuit was fine.

I plan on double checking the inside ground, but I triple checked all the exterior grounds and gave an extra sanding to each location to make sure there was a good ground.

any insight is appreciated.

[1967KaiserM715]

Grounds checked, double checked, cleaned, several new grounds added with no change.

It also appears some of my gauges don't function correctly, oil pressure says at 80psi key on or off, doesn't move, fuel gauge is random and last two times needle drops to empty before slowly rotating and settling at about 3 o'clock past full. Engine coolant temp actually appears to be fine.

I will also add I used the stock harness from the truck-originally a 305 with a 700r4. I then proceeded to copy the wiring diagram from a 1985 6.2 Diesel and added the Glow Plug Circuit, Fuel Heater, Water in Fuel Sensor, and anything else need. For example, the Choke wire used the same circuit as the fuel heater, and with no choke I simply used the wire and spliced the right connector in place. Same with Fuel Shut off and HEI power.

I also added three gauges and used a LPS Circuit(green space) for lights(work and dim with gauges) and I also used a Bat spot and several IGN spots for various items(I believe a trip wire for fuel pump relay is biggest one.)

I'm stuck in doing anything else, I absolutely hate wiring, as long as I don't need lights or directional's or some gauges, everything else works great.

[bd]

...have the rear harness disconnected, the harness that mounts to the truck bed appears to have a short somewhere between the brakes and parks/turns....

My symptoms, no drivers/left side park lamps, passenger/right side lamps do work, no turn signals, hazards do work-I switched relays, everything remained the same. I have nothing on right side turn signals-no indication of wanting to flash, no dash light. Left turn is a little more fun, low coolant light flashes, seatbelt and buzzer flash, glow-plugs will flash, and dash left turn will flash. the left side dash turn will also stay lit, although it does it randomly. Lights still don't work.

...Dash lights appear to work fine as long as the rear body harness is disconnected....

Clarify please - do the symptoms occur with the rear lamp harness disconnected or connected?  OE thermal flashers have a minimum current load, below which they will remain on and not flash.  So if the rear lamps are disconnected, normal flasher function may be impaired, especially if the flasher is weak.

Regarding the rear lamp harness, inspect the section of harness inboard of the frame where it passes above the rear axle in proximity to the original small block exhaust pipe.  Severe heat damage to the harness is common in this area and can result in aggravating shorts and grounds.  Also, follow the harness along the frame and look for any spot where wire insulation may be chafed, such as where wires pass through frame clamps.

Remove and physically inspect all of the exterior bayonet base bulbs and sockets to verify that the CORRECT bulbs are PROPERLY installed and that there is no corrosion hidden inside the sockets.  Verify that each socket is properly grounded by probing the socket housings with the bulbs installed and lights switched on.

If no problems are discovered, disconnect the turn signal switch below the steering column and feed B+ via a 20-amp fused jumper to each of the dash harness pins while an assistant watches the external lights (turn/hazard switch harness colors: Lt Blu = LF turn, Yel = LR turn/brake, Dk Blu = RF turn, Dk Grn = RR turn/brake, Wht = B+ from brake switch, Ppl = I+ from turn flasher, Brn = B+ from hazard flasher, Blk = horn, Lt Grn & Tan = key warning switch pair).

[1967KaiserM715]

No turns with rear harness connected or disconnected, hazards worked fine when connected, fuse T/L CTSY blew immediately when turning on parking lights. With fuse replaced, and not turning parking lights on, the brakes would illuminate the rear parking lamps.

I will verify everything, plus pay special attention to how the dual function bulbs in rear work with hazards, although it will be a few days, currently out camping at a military vehicle rally.

I did replace a bunch of bulbs when a couple didn't light initially, before realizing there was some deeper fault. I had completely removed the harness, and everything did work previously, with exception of passenger rear brake.

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[1967KaiserM715]

So I found my short in the rear harness, a mistake of which I take full blame for not verifying proper wires, PO had a ring terminal on what appeared to be a black wire, it was much darker then the other brown, I assumed it was a ground, but it appears it is supposed to be maybe the license plate light.

So that fixed that problem, although I may need to find some bulbs, because it appears my drivers front parks still won't come on, but I haven't tested off vehicle again. I will follow through with your testing 'bd', and post results later, as turn signals are still non functioning.

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[1967KaiserM715]

So results, bulbs work fine out, good ground, but still no park lamps on drivers side.

Using a B+ 20 amped fused probe,  Lt Blu= LF Turns on, Yel=LR Turns on, Dk Blu=RF Turns on, DK Grn= RR Turns on, Wht=nothing, Ppl=Glow lights, Low Coolant, Seat belt lamps flash, glow plug solenoid turns on, no turn lights, Brn=nothing, Blk/I assume Dk Grey in my truck=nothing(also horn and windshield wipers do not work.) Lt Grn=nothing, Tan=sparks, blows probe fuse.

Now I would have thought applying power to the B+ from brake switch would have powered the brake lamps-but didn't, same with Brn/B+ from hazard would have lit the hazards, but they didn't.

[bd]

If no problems are discovered, disconnect the turn signal switch below the steering column and feed B+ via a 20-amp fused jumper to each of the dash harness pins while an assistant watches the external lights * (turn/hazard switch harness colors: Lt Blu = LF turn, Yel = LR turn/brake, Dk Blu = RF turn, Dk Grn = RR turn/brake, Wht = B+ from brake switch, Ppl = I+ from turn flasher, Brn = B+ from hazard flasher, Blk = horn, Lt Grn & Tan = key warning switch pair).

Oops!  I got distracted and snarled my post, leaving out an important part at the * in the discussion quoted above.   Foolishly, I left out:

"Connect a fused jumper, in turn, to wires Lt Blu, Yel, Dk Blu, Dk Grn.
"Wht, Ppl and Brn are power inputs to the turn/hazard switch - probing these wires with power will backfeed the electrical system giving "odd" and "unexpected" results.
"Blk is the horn relay ground controlled by the horn button on the steering wheel.  Grounding this wire should sound the horn.
"Lt Grn & Tan are for the key warning buzzer and should not be probed.

Your tests indicate that the chassis wiring tor turn/hazard/brake is all intact.  Now, check for power on the brown wires connecting to all of the front park and side marker lamps.  If the brown wires are hot with running lights on and the bulbs are good and properly indexed in their sockets, but the bulbs still don't illuminate, probe the socket housings to see if your test light illuminates.

[1967KaiserM715]

"Wht, Ppl and Brn are power inputs to the turn/hazard switch - probing these wires with power will backfeed the electrical system giving "odd" and "unexpected" results.Now because I replicated the exact symptoms I am having with the turn signals, by probing the Ppl, could that indicate that my switch is bad and backfeeding?

I want to double check my cab ground, I can't remember if I made a cab to frame, and that my cab to engine ground is not enough/good through the engine.?? I plan on taking a test lead and running a wire straight from the battery negative to the under dash ground...or I can just run my multi meter negative probe to dash ground and check voltage at positive battery terminal, shouldn't see more then a .30V drop I would assume.

[bd]

Now because I replicated the exact symptoms I am having with the turn signals, by probing the Ppl, could that indicate that my switch is bad and backfeeding?

If you think the turn signal switch is the problem, plug a new one into the harness under the column.  You don't have to install it in the column just to check circuit function.  Purple is 12-volt ignition through the turn signal flasher.  Do you measure battery voltage on the purple wire when the ignition is switched on with the turn switch unplugged?  BTW - install a new turn flasher using one of the newer electronic varieties instead of the original thermal flasher.  Electronic flashers cycle based on an internal oscillator rather than current load (which is dependent on the bulbs), providing a very consistent flash frequency regardless of load.  In contrast, thermal flashers will not flash if the current load on the flasher is insufficient.

I want to double check my cab ground, I can't remember if I made a cab to frame, and that my cab to engine ground is not enough/good through the engine.?? I plan on taking a test lead and running a wire straight from the battery negative to the under dash ground...or I can just run my multi meter negative probe to dash ground and check voltage at positive battery terminal, shouldn't see more then a .30V drop I would assume.

Connect your voltmeter between the battery negative post and the common grounding point under the dash.  With symptoms occurring the voltmeter should measure <0.1 volt.  If not, there is a floating ground.

[1967KaiserM715]

Ok, so found a bad ground on the front turn signal, the grounding tab came out with the bulb, must have been weak, and my repeated pulling finally broke it off completely, and is why when probing the socket and checking ground continuity, it checked fine, bulb pressure on tab may have separated contact. So now no funny stuff, and left turns work, but still no right turns. New bulbs and swapping bulbs have no effect. I took an unknown working turn switch and plugged it in, but nothing worked, so likely that switch is bad.

I'm only partially tempted to throw a new switch at it now, hoping something obvious will pop it's head out soon.

Also do plan on getting LED bulbs, especially for brakes, so an electronic flasher is on the list.

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[1967KaiserM715]

OK Same D*** issue, left turn lights up the whole dashboard, nothing on the right, a new switch** does nothing(un-installed, just plugged in.) Brand New AC-Delco bulb socket, GOOD GROUNDS, adding extra grounds running directly to lights from batteries and to the in cab ground does NOTHING.

installed an electronic Flasher-Same thing.

** Hazards Work, grounding horn work, just turn signals do nothing.

[bd]

Electrical gremlins can be frustrating!  I'll try to help you through the weekend if you'll be available.  In a new unit of time, with the turn switch unplugged from the harness under the column, feeding fused B+ to the light blue and then the dark blue wires of the harness, describe what occurs - which lights illuminate.

[1967KaiserM715]

Dark blue-right front turn and side marker.

Light Blue- left front turn and sidemarker.

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[1967KaiserM715]

Only have 6v on ppl wire coming into turn switch- also realized the left turn works with key off and out-never put the key in today.

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[bd]

Dark blue-right front turn and side marker.

Light Blue- left front turn and side marker.

In either test, did the dash turn indicators illuminate?  Did any dash lamps illuminate?

Only have 6v on ppl wire coming into turn switch- also realized the left turn works with key off and out-never put the key in today.

Does the PPL wire measure 6 volts with the key ON or OFF?  So, the left turn works only with the ignition OFF and the right turn never works, yet all four corners and dash indicators flash normally when the hazard flashers are ON, regardless of ignition being ON or OFF?