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73-87 Chevy _ GMC Trucks => Electrical => Topic started by: Thesrvfan on April 05, 2019, 08:14:27 AM
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Hi everyone. 78 C10 has weird lighting problems. I have hazards on all corners BUT rear drivers side. I have a brake light on passenger side. I have both tail lights. I have no turn signals at all. I have replaced the turn signal switch and flasher. Any help would be appreciated! Thx
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Did you check all your grounds? Do you have the correct bulb wattage? If you "upgraded" your bulbs to led that could cause issues as well because they have very little draw and you usually need get a flasher ment for the led bulbs. How did the connections look at the wiring harness where the pigtail from the switch plugs into? Could they be loose or corroded?
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Thanks. I have standard bulbs and a new flasher unit on the fuse block.
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Welcome.
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Welcome.
Thanks!
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If you have only 1 flasher unit on the fuse block that is for the 4 way flashers. There is another under the dash for the turn signals
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Thanks Zieg, I have two flashers on the fuse block.
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check and clean the ground behind the left rear tail light
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Thanks Irish
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Download my scan of the 1978 GM Light Truck Wiring Manual from this post and possibly the Unit Repair and Service manuals as well.
http://forum.73-87chevytrucks.com/smforum/index.php?topic=30115.0 (http://forum.73-87chevytrucks.com/smforum/index.php?topic=30115.0)
The column switch depiction is centred toward the RH edge of the first wide page.
You'll note that there are two completely separate flashers in the 1978 cab wiring. The original flashers were bi-metallic heater strips with control contacts directly inline with power to the circuit that needs to be intermittently broken.
The Hazard switch flasher is mounted on the fuse panel. Output to the column is Brown Circuit 27. The Hazard flasher gets power from the 15A AGC fuse marked "STOP LPS". This is working so we're moving on...
I have no turn signals at all. I have replaced the turn signal switch and flasher.
I assume you changed the Hazard flasher and didn't know about the additional hidden Directional flasher buried in the wiring near the fuse panel.
The directional flasher is supposed to be hanging on a hook on a black a rubber band near the fuse panel or tucked up into the wiring nearby.
It'll look something like this Kawasaki flasher if it still has the original black rubber band after 41 years.
(http://johnnynightstick.s3.amazonaws.com/IMAGES/Kawi%20Relay%20with%20mount.jpg)
It'll have a Blue and a Purple wire with the funny 90° two terminal Packard 56 flasher connector, and the directional flasher, dangling from them. Get a flashlight and go looking for it. There is sometimes an empty directional flasher position on the lower LH side of some American Glass Cartrige fuse blocks but GM didn't originally use it.
Output to the column from this flasher is the Circuit 16 Purple wire.
The Directional switch flasher Ignition Switched power is on Circuit 38 Dark Blue wire it's spliced to the Backup Lamp power wire (Circuit 75 Dark Green) on the Packard 56 Neutral-safety/Backup-lamp connector at the base of the steering column.
There's a 15A AGC Glass fuse marked "B/U LPS DIR SIG" in the fuse panel. Check with a meter or a test lamp that both ends of that fuse have battery voltage with the ignition switched on.
Check for battery volts at the Dark Blue wire on the directional signal flasher plug.
If the socket has juice with the ignition on borrow the working 552 hazard relay to test. The original directional relay is a 224 (2 lamp model). I usually just use the 552 (2-6 lamp model) Hazard relay or an electronic relay.
I usually use a fat rubber band to hold the relay to the metal bracket but you can find an original-ish type rubber mount if you search for Honda, Kawasaki, Suzuki, etc motorbike directional flasher mounts.
I have hazards on all corners BUT rear drivers side. I have a brake light on passenger side.
The Brake switch power to the rear filaments is run from the pedal switch through the white wire on the harmonica plug, up to the column switch and out through the Dark Green LH and Yellow RH Bright filament wires to the bright filaments in the tails.
Since all four corners light up with the hazards. This means the wiring from the harmonica plug to the Bright filament of all four bulbs is working. It wouldn't hurt to remove the bulbs from the plastic taillamp housings and verify that the Bright Filament of the 1157 bulbs in the tails is really the one that's actually glowing.
Since both Tail Lamps light... likely the grounds to the bed sheet metal behind the LH & RH tails are OK but it doesn't hurt to check them both.
You have a right hand brake light but no left hand. You can check the column switch pretty quick right at the harmonica plug with a test light or a meter. The Dark Green and Yellow wires at the harmonica plug should have battery power when you push down the brake pedal. Since your LH BRAKE/DIRECTIONAL isn't lighting probe the conection on the Dark Green wire with the pedal down.
No juice? The column switch is knackered.
If it has juice then test for juice on the BRAKE/DIRECTIONAL terminal in the LH bulb socket. No juice there? Climb under the back and fish around on the LH frame rail for the butchery that U-Haul or Ryder or ... did to your tail harness. Worst case the 4 terminal molded disconnect is knackered but usually it's the result of some teenager with scotchloks and too little experience.
If the four position disconnect is completely knackered you can update it to the 1985 and later four position 2x2 Weatherpak connector fairly easily. Download the '85 or '86 wiring diagram for the factory pinout so you can make use of the Hopkins waterproof plug-ins for trailer wiring.
I've replaced the wire from the bulkhead plug to this connection. The original wires were skinny little 18ga wires. I use four 16ga SXL wires in factory colors... DK Green, LT Green, Yellow, and Brown with Male Packard 56 terminals on one end and Weatherpak terminals and seals on the other. Slip some 1/4" split poly or expanding mesh wire cover over the length of the wires to keep em safe and tie em off to the frame using the GM clips.