dash lights come on when I depress brake/no brake lights
 

Thanks for reading about my issue. This question pertains to my 1966 GMC short bed. Hope you can help. I took my truck out of storage this week and discovered a new issue. I'll try to be brief. First, I've read a lot of forum material and came up with some good tips. That being said, I was wondering if anyone has had my specific prob? All suggestions welcomed.

PROBLEM: I don't have tail lights or brake lights. However, when I depress brake pedal (engine running and off) the dash lights go on. Still not brake lights.

WHAT I'VE DONE: 1.) I wiggled a few connectors under dash. No change.
2.) I followed a wire from rear driver side to its plug on the upper right side of fuse panel. I pulled the plug and wired off both socket and plug. Fuse looked ok.

3.) I removed the two screws holding the fuse panel to the fire wall. I wire cleaned screws and thread openings and reinstalled fuse panel.

4.) Fixed. I depressed brake pedal and no more dash lights and tail lights worked.

BAD NEWS: I went out today to check the repair. Well, as you might guess, the problem is back. It's like the power to the brake like switch flows directly to dash lights. So, now I'm coming to you.

PAST: I've owned the truck 3 years. It has a few gremlins to say the least. The first year I owned it, the right tail light did not work coming out of storage. I cleaned up connections including the mount to fender, and, light worked. Thought this was worth mentioning as it was a grounding fix.
A couple of times I've heard the horn honk while turning right. Yikes -- but certainly not a regular occurance.

POPS

Re: dash lights come on when I depress brake/no brake lights
 

Well, I don't know if you have a printed circuit board behind the gauges or not. I am assuming you are talking about gauge illumination bulbs. You have a gray wire for the bulbs. The gray wire goes thru a instrument panel connector to the fuse panel. On the Fuse panel it is near a green wire that goes to the headlight switch. One of the wires from the brake switch (orange) goes to the headlight switch also. That orange is a hot wire I think. So some how via those connections or at the fuse box, somebody is touching somebody they shouldn't be. We could never tell you exactly what's wrong there. Just letting you know you need to study a wiring diagram and focus on those wires. Also be sure your actual brake pedal arm is not hitting/moving wires when you push on the brake. That arm and it's linkage or clutch arm can be right near all that wiring birds nest and physically forcing a contact between wires or fuse terminals. The evidence for this is the fact you jiggled it and it changed the wires enough but now they are getting smashed/torqued again. Don't know.
My wire colors could be wrong or your wires could be changed. So don't go by colors, go by the function and a wiring diagram

Your cleaning of the panel mounting screws have no bearing on anything. The fuse box is not grounded. All grounding is at the component. From battery to motor to chassis to body. Other than those connections, there are very few ground wires running around. Fuse box is all hot. It sounds like you need to completely take out fuse box someday and "refurbish" all wiring and connections. With the history I read, your truck is NOT reliable for a road trip.

Just keep reporting your progress and we will be glad to stay with you.

Re: dash lights come on when I depress brake/no brake lights
 

I believe the problem is a grounding issue at the rear of the truck, or maybe between the bed and the frame. When you step on the brake the power travel through your brake light then through your tail light back the your dash light to ground. By not have a ground at the brake light it seek the ground through the tail light circuit. To check this theory place the truck in the garage with no visible light on (total darkness). Have someone step on the brake. The dash light will come on and while someone else is looking at the tail light it should glow very dimly (the current is limited by the bulbs in the dash). Or you can run a jumper wire from the battery ground (Negative terminal) to the base of the tail light and see if the problem goes away. The grounding problem can be cause by either the tail light assembly not making a good ground to the bed or the bed is not grounded to the frame (or maybe a little of both).

Hope this help. :thumbsup:

Re: dash lights come on when I depress brake/no brake lights
 

Thanks for responses gentlemen.
James I hope you are right. I have read of individuals who changed their entire wiring system because they couldn't find out what was causing lights to work and not work. It has become almost universally understood that ground gremlins are the source of most problems.

Earlier this evening I was cleaning and re grounding wires under dash. No change. I went to driver's tail light assembly and pulled the boot off the back of the brass bulb parts and noticed corrosion (boot was not properly installed on the bracket so moisture got in). I brushed and cleaned contacts and even the two bolts that hold the bulb housing. I added some dialectic grease and reassembled. Tuned on lights - still no tail lights. I pushed the bulb in and noticed a faint glow.. Hurray. I will do more grounding work around tail light assembly tomorrow. I think you are definately moving me in the right direction. (Is wire brushing contact points or using dialectic lube a bad idea?)

I read of people adding ground wires from tail light assembly to frame. Do you recommend? Also would your use one of the existing bolts on the tail light brackets? also, what guage wire would you use?
Thank you sir for any and all help.

Re: dash lights come on when I depress brake/no brake lights
 

Ken. I agree with your input. I didn't notice any wires getting bumped by clutch or brake pedal. I did notice that one connector was fine but the plug was a little loose. Otherwise no obstructions or weakness evident from appearance.
I would be more secure with a new panel. are they available. wouldn't be hard to change unless I missing something. do you recommend a parts source?

Re: dash lights come on when I depress brake/no brake lights
 

I would recommend adding a 10 gauge wire (using ring terminals) between the rear of the bed and the rear of the frame (a short run of wire with enough slack for flexing a little). Once the metal is clean to the metal and the wire is secured, spray primer over the connection to help protect the connection. The hardware that hold the light assemble to the bed are known for corroding, make sure it also clean/new. Also make sure from the battery negative to the frame as well as the battery negative to the engine is good. Same goes for the battery positive to the starter. In summary if it look corroded/dirty its not making a good connection.

I heard of several cases where the engine ground was bad and the only ground path from the frame to the engine was through the transmission linkage. The transmission filled up with metal particles because the starting current ate up the parts (from electrolysis).

Dialectic grease is good for the inside of the connectors and bulb sockets.

Hope this fixed it for you.

Re: dash lights come on when I depress brake/no brake lights
 

Sooo, this morning I reexamined the driver side tail light assembly. What I found is that the brass tube that holds the bulb and pushes through the tail light housing was gritty and a tad rusty. I removed the tube and cleaned the tube and the hole that it slides through. I turned on the lights and they worked; both sides. Hurray. I turned on the turn signals and they worked on the right only. Dash light still shows when i depress brake. I will get to grounding frame to bed and then install a new bulb on the left. Progress! Hope this helps others. by the way, I have aftermarket tail light assembly and it doesnt seem right to me that the brass tube would turn at all??? junk assembly??

Re: dash lights come on when I depress brake/no brake lights
 

Do you have pictures of old vs. new light assemblies?

Re: dash lights come on when I depress brake/no brake lights
 

FYI: You should also check the light sockets in the hood too. I believe your 66 is the same as mine 64 in regards to the turn signal and dash indicator. You only have one indicator for both side. If this is true that indicator bulb get it ground by the front turn signal bulb that is not lit up (bulb connected in series). So if the left turn signal is flashing, the power that feeding the left front signal is also feeding the indicator bulb. Then the indictor ground through the right turn signal bulb (the right side does not lite up because the indicator bulb is limiting the current).

Hope this does not confuse you, if it does let me know we'll fix it.

Re: dash lights come on when I depress brake/no brake lights
 

Feedback from 6066 members has been a blessing to me. Thank you and God bless. I can only imagine how much you saved me had I dropped this off at a shop.
So here's the report. Hope it's a help to others:

1. As indicated above, the brass socket was lose where it exited the tail light housing. This was part of problem. See #4 below.
2. I put a circular wire brush on drill and cleaned (to bear metal) existing holes on frame and tail light brackets that would be used for grounding; also brush-cleaned bolts, nuts, and washers. Also sprayed with electrical cleaner.
3. Used 10 gauge wire and ring terminals to ground the frame to light brackets, and, frame to rear of bed (3 wires in all; nothing excessive in length). I didn't have ring terminals large enough to use in existing holes in frame so I stripped about 3 inches of wire jacket, twisted the wire and then rolled it around the bolt that was sized appropriately (about 1/4") for the hole in the frame. I then took the bare wire in its rounded shape and melted solder on it (this worked great and it didn't break or distort when bolted down between the two washers). I used flat washers and lock washers at each bolt area.
4. When all was completed, I was pleased to see blinkers, tail lights, brake lights, and NO dash lights.:upyes:
5. I put the lenses back on and went to try everything out just to confirm a done deal. Dash lights were back when I depressed the brake and left tail light was malfunctioning. I wiggled the tail light boot at back of housing and the light worked fine. So, I removed the lens, got my drill out and drilled some material away to clean spot at edge of brass socket and housing to assure the solder would join the two components. Spot soldered the socket to housing. As of this typing, NO issues found at dash or rear lights.
6. Per the advice of forum helpers, I'm going to reground front of truck and anything that deals with headlamps. Also, I will be skimming the bear metal areas with silicone or prime to inhibit rust or corrosion.

THANK YOU - and God bless you helpers. Very helpful forum support!

Re: dash lights come on when I depress brake/no brake lights
 

Kudos to James.