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Old 02-15-2022, 10:59 AM   #1
gschroeder
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No Tail Lights or Rear Side Marker Lights

I have a freshly restored 1970 C10 with tail lights and rear side marker lights not working. Brake lights work, and turn signals work, but no tail lights or rear side marker lights. I confirmed with a test light there there is power coming to the tail light and side marker light socket. Side marker light grounds are hooked up, and bed is grounded to the frame. I tried using the test light as a temporary ground, but still could not get the tail lights or rear side marker lights to work. Any suggestions on what to do? Thank you for your help. Thank you
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Old 02-15-2022, 04:21 PM   #2
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Re: No Tail Lights or Rear Side Marker Lights

If you get continuous 12V at the socket when the lights are on - one test lead on bulb socket and the other on the + "nub" in the socket, I would think either the socket is corroded or the bulbs are bad?
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Old 02-15-2022, 06:32 PM   #3
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Re: No Tail Lights or Rear Side Marker Lights

Run a short wire from the brake/turn/tail socket to the marker light socket. If your brake /turn lights are working then their sockets are grounded and if you have 12v at the marker lights then their sockets are not grounded and the wire should ground them.

The tail light wire and marker lights wires are brown, so you may not be getting power to the tail light filaments in the brake/turn sockets because of bad sockets or those 2 bulbs might be bad as bhap has suggested, and your two marker sockets may not be grounded.


Here is a wiring diagram showing how the markers are wired and the tail lights.

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Old 02-17-2022, 08:48 AM   #4
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Re: No Tail Lights or Rear Side Marker Lights

bhap, VetteVet, thank you for your help. You were both correct with your diagnosis. Tail light bulb socket had a little corrosion, and side marker lights were not grounded well enough. I cleaned the tail light bulb socket, and grounded the side marker lights to the rear cross sill, and all is well. Thank you for your help.

May I ask for your help with another electrical gremlin. My reverse lights are not working. I tested the light socket on both sides, and I have no power back there. How can I troubleshoot this? Truck has TH350 auto trans. Thank you again for your help. Thank you
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Old 02-17-2022, 01:07 PM   #5
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Re: No Tail Lights or Rear Side Marker Lights

Maybe your reverse/neutral safety switch on the steering column has dirty contacts or it is out of adjustment. Do your reverse lights come on if you move the shifter lever slightly away from the reverse position in either direction? If yes, then you just need to adjust the position of the switch. If not, then you could jump the light green and dark green wires together on the switch connector with a short piece of wire. If the lights come on, then you know the issue is with the switch.
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Old 02-17-2022, 01:44 PM   #6
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Re: No Tail Lights or Rear Side Marker Lights

pjmoreland, thank you for your reply. I did try moving the column shifter away from reverse in both directions, and still could not get the reverse lights to come on. I will try jumping the light green and dark green wire on the neutral safety switch and see if they come on. If they do, I will replace the switch. Thank you for your help. Thank you
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Old 02-17-2022, 02:31 PM   #7
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Re: No Tail Lights or Rear Side Marker Lights

Be sure to check the dark green wire for power before you blame the switch. Don't forget to turn on the key switch.
If you do a continuity check on the NSS it will tell you if it is bad also.
I'll have to check the fuse panel, I can't remember if there is a back-up light fuse.

Yes there is a 10 amp fuse. Check it and be sure the clips that hold it are clean.
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Last edited by VetteVet; 02-17-2022 at 02:38 PM. Reason: more info
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Old 02-17-2022, 09:34 PM   #8
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Re: No Tail Lights or Rear Side Marker Lights

VetteVet, pjmoreland, thank you for your help. I jumped the dark green / light green wire at the NSS, and reverse lights turned on. I will replace the NSS, and that should take care of the problem.

Sorry, could I ask your advice on 1 more electrical gremlin? I recently installed a new fuel gauge because it was bad, but now the idiot temp light and idiot brake light turn on when I turn the lights on (and go off when I turn the lights off). I believe these idiots lights are only supposed to turn on when the key is in on position before start up (and of course if the engine overheats or brakes fail). They do not turn on when I put the key in the on position. Only come on when I turn the lights on. Any suggestions on how to trouble shoot this? Thank you again for your help. Thank you
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Old 02-17-2022, 09:50 PM   #9
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Re: No Tail Lights or Rear Side Marker Lights

Quote:
Originally Posted by gschroeder View Post
I will replace the NSS, and that should take care of the problem.
It could just be that the NSS slider isn't properly engaged with the tang on the shift tube. It could also be that the internal contacts are gummed up and just need to be cleaned. You can disassemble the switch by bending the metal tangs open on the backing plate. I had to clean the contacts on my current NSS. Personally, I'd rather have an original switch that has been cleaned up than a reproduction switch.
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Old 02-18-2022, 02:25 AM   #10
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Re: No Tail Lights or Rear Side Marker Lights

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Originally Posted by gschroeder View Post
I believe these idiots lights are only supposed to turn on when the key is in on position before start up
The brake warn and temp idiot lights should only turn on when you are cranking over the engine. The "Generator" and oil pressure lights, on the other hand, light up in the run position before the engine is started.

By any chance did you leave out the plastic shield that sits behind the fuel gauge, shown below? Or maybe it fell out of position. If it's not in position, then the light from the gauge cluster back-lighting bulbs would shine through the warning light lenses when your lights are on. The photos below are of a full gauge cluster, but I believe the fuel gauge portion is the same as yours.
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Old 02-19-2022, 06:03 PM   #11
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Re: No Tail Lights or Rear Side Marker Lights

pjmoreland,

I took the fuel gauge back out, and the plastic shield was in place. However, apparently the manufacturer forgot to paint it, and the dash lights shined right thru the clear white plastic. I took the plastic shield out of my broken fuel gauge (that was painted), and installed it. Dash lights no longer shine thru.

However, my temp and brake idiot lights do not work. They do not illuminate when cranking engine. They also do not illuminate when I unplug the temp sensor and brake wire at master cylinder. I did confirm the bulbs are good. Can you help me trouble shoot this? Thank you again for all your help.

Thank you
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Old 02-19-2022, 08:42 PM   #12
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Re: No Tail Lights or Rear Side Marker Lights

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Originally Posted by gschroeder View Post
pjmoreland,

I took the fuel gauge back out, and the plastic shield was in place. However, apparently the manufacturer forgot to paint it, and the dash lights shined right thru the clear white plastic. I took the plastic shield out of my broken fuel gauge (that was painted), and installed it. Dash lights no longer shine thru.

However, my temp and brake idiot lights do not work. They do not illuminate when cranking engine. They also do not illuminate when I unplug the temp sensor and brake wire at master cylinder. I did confirm the bulbs are good. Can you help me trouble shoot this? Thank you again for all your help.

Thank you
The temp and brake lights work by being shorted to ground by the sensors, so disconnecting them won't make the warning lights turn on.

Check your fuse panel. I'm not at a computer right now, but I believe your warning lights and fuel gauge are powered by the same fuse - possibly the cluster feed fuse.
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Old 02-20-2022, 12:30 AM   #13
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Re: No Tail Lights or Rear Side Marker Lights

You can test the two lights by turning the key on and grounding the green temp wire and the brown wire to the brake master cylinder. The lights are illuminated normally by the wiring connections on the key switch which are separate
grounds from the hot wires on the key switch. If you don't have two green wires and two brown wires on your key switch it may be the wrong switch.

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Old 02-20-2022, 02:25 PM   #14
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Re: No Tail Lights or Rear Side Marker Lights

pjmoreland, VetteVet, thank you for your advice. I checked the fuse panel, and the 3 amp cluster feed fuse was blown. I replaced it, but still no idiot brake and/or idiot temp light working. I tried manually grounding the brown brake wire at the master cylinder, but could not get the light to illuminate. FYI, I checked the light bulbs again, and both do work. I put the lights in a different socket, and both illuminated just fine.

I also checked the ignition switch, and there are not 2 green wires running to it. I attached a pic of ignition wiring. There is red, purple, pink brown (large), and 2 small brown wires. No green. I'm not sure if I mentioned this earlier, or if it matters, I do have the factory deluxe CST10 dash with all gauges and tach.

Any suggestions on what to trouble shoot next? Thanks again for all your help.

Thank you
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Old 02-20-2022, 04:41 PM   #15
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Re: No Tail Lights or Rear Side Marker Lights

Just a quick note during a busy day - The temperature warning light is nonfunctional on a full gauge cluster. The brake warn light should light up when cranking the engine though.
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Old 02-20-2022, 05:54 PM   #16
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Re: No Tail Lights or Rear Side Marker Lights

I believe the two tan wires visible in the photo of your ignition switch are for the brake warn light. One goes to the master cylinder, and the other goes to the light. The ignition switch connects the wires to ground when cranking the engine.
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Old 02-21-2022, 12:44 PM   #17
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Re: No Tail Lights or Rear Side Marker Lights

pjmoreland, VetteVet, I wanted to let you know I will start a new thread for this idiot temp light - idiot brake light not working problem. Somehow I got way off topic from the original tail light thread. I appreciate all your help, and look forward to hearing any suggestions you may have on the new thread. Thank you
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Old 03-04-2022, 10:46 PM   #18
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Re: No Tail Lights or Rear Side Marker Lights

Guys, I installed the new NSS, and it solved the problem with my reverse lights not working. Unfortunately, I can only get the reverse lights to illuminate when I move the shifter past reverse all the way into neutral. I did adjust the NSS as far left (counter clockwise) as possible. I also double checked to make sure the NSS was aligned with the metal tab/slot in the column. Is there some another adjustment I can make somewhere else? Is my brand new NSS bad? I guess I could make the slots bigger/longer on the NSS, but it seems like I may have something else out of alignment. Thanks again for your help. Thank you
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Old 03-04-2022, 11:39 PM   #19
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Re: No Tail Lights or Rear Side Marker Lights

Maybe the shift rod that goes down to the transmission needs to be adjusted where it attaches to the steering column. If it isn't adjusted properly, then it will affect where the NSS needs to be positioned.

Last edited by pjmoreland; 03-05-2022 at 02:25 AM.
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Old 03-05-2022, 11:00 PM   #20
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Re: No Tail Lights or Rear Side Marker Lights

pjmoreland, thank you for the tip. I adjusted my steering column, and reverse lights are working properly. Thanks again for your help. Thank you
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