Instruments panel lights up when brakes applied?

[wwotr]

I've got my 72 GMC Shortbed Fleetside at the shop.
One of the things my mechanic asked me was to post on the board about this problem:

When the lights are off and the Brake is applied, the Instrument Panel Lights- Light up.

Now they also go on as they should when the Headlight switch is pulled out and I notice,
NO DIMMING of the Instrument Panel Lights when the Brake is applied.

I seem to remember a similar problem on my 67 C-10, but that was so many years ago.............. (and another Mechanic).

I thought some of the better informed 67-72 owners might know...like "
Oh hell yea thats a common problem on those Trucks. Just take XXXXX and do XXXX and your good to go".

I wanted to hopefully find out what it is a have my mexchanic remedy it BEFORE I pick it up on Monday.
Any Links/thoughts/opinions would be appreciated!

Roger
"RATIKLE"

[cparman]

my first thought is that you have a turn signal bulb/brake light bulb that if back feeding voltage thru the instrument cluster. I have seen this a time or two. Visually check all of the bulbs to be sure that there is not a damaged element in one of them

[Blazer1970]

It could be a bad bulb, or more likely a bad/missing ground in the tail light harness.

[El Jay]

I'd start out by checking ALL your grounds.

I know it sounds stupid, but a bad ground in one place can do really weird stuff in a totally different area.
Don't just "eyeball" the ground connections. Take them apart & make sure everything is clean & shiny for good connectivity.

[ajcan]

I am new to this forum and to the older trucks but I have been an import mechanic for 15 years.I have seen single element bulbs in dual element sockets and vise verse cause many lighting problems.
That is by far the easiest thing to check.Another way to tell is see if your parking lights are coming on and you just don't realize when you hit the brakes.Just my 2 cents.Hope it helps.

AJ

[ERASER5]

This use to happen once in a while at dealerships on new cars. Some yo-yo would put the 1156 bulb in the 1157 socket. When the brake is applied, the power back feeds the parking light circuit including the dash. Sounds like your problem.

[STOCKISH]

Usually means the wrong bulb was put in the taillight socket. I'd start there for sure. See it alot around here for some reason.

[Longhorn Man]

like many of the others said, I would start with 2 brand new 1157 bulbs in back.
The ground thing, not likely. Easy enough to fix though, but the electricity would take the path of least resistance, and that would be through the back up lights 9 times out of 10. See it all the time on trucks at work.

[Tx Firefighter]

When I first read the post, I was thinking I've never heard of a mechanic asking his customer to post on the web looking for repair advice. Seems like it would undermine the customer's confidence.

[Longhorn Man]

so true! Esp for something that is more likely than not, just a bad bulb.
Was anyone else learning this stuff in high school?

[kamikazekyle05]

I posted about this not too long ago. I had the same problem put some new bulbs in the taillights and problem solved

[wwotr]

Thanks to ALL of you who came out of the woodwork to help me with this problem.

Upon CLOSER INSPECTION, I found :
Drivers Side Tail Light: No 1156 Back-up Bulb in the Socket.
Passengers Side Tail Light: An 1156 Bulb in the 1157 Socket.

I'm putting new lenses/Bulbs when I get back into town on Wednesday (next week).

On top of THAT, when I took out the old ("Under Dash Stereo"),
it had 3 Ground Wires that were screwed in under the Dash.
I didn't pull them out yet, because I THINK they may go to some of the Gauges. I'll need to take a look at that as time alows.

Thanks Again to EVERYBODY!
Roger

[ERASER5]

Originally Posted by Tx Firefighter

When I first read the post, I was thinking I've never heard of a mechanic asking his customer to post on the web looking for repair advice. Seems like it would undermine the customer's confidence.

I never heard of that either. If I have to educate my mechanic, he'd better have a particular machine that I don't, like a tire machine. A parts counter guy, I don't mind educating. Nicely. If I start getting warm, it is time go to the next store.