Dash Panel Issue

[Classics Fan]

Before I pull the dash panel in my 71 Jimmy I’m hoping someone has some ideas of what to look for to fix the problem I’m having.
This is a duplicate post from the 1969-72 Blazer and Jimmy forum to get more eyes and hopefully, thoughts and ideas.


When I bought the Jimmy in late 2018 it had an intermittent problem where, when the headlight knob was pulled out, the panel lights would go dim, the high beam indicator would illuminate when the headlights were on low beam (and would go out when they were out on high beam), and both left and right turn indicators would glow. In this condition when the turn switch was flipped in either direction the corresponding dash indicator would flash off and on (normal operation is the indicator is unlit until activated and then flashes). Until recently a rap or two with knuckles on the top front center of the dash panel would fix the problems. However this isn’t the case any more. All the conditions I’ve described are now constant and not intermittent.

My thought is either the printed circuit has a problem, there’s some sort of short in the circuit, or a bad ground. Anyone run into this before? Thoughts, ideas or suggestions?

[PanhandleShantyman]

When I got my '69 GMC 1500 last year, it had a similar issue with the indicators turning steady on whenever the headlight switch was activated. The turn signals themselves would work, as yours do, but would also flash significantly slower with the headlights on than when the headlights were off.

In my case, the problem turned out to be lack of ground at the turn signal lamp bulb housings themselves at the front of the truck. One side had the original lamp housing and just needed sanding down to clean metal to restore ground. the other had a replacement lamp housing with an actual ground wire (not present in the original housing) that had never been connected anywhere. I fixed those issues and the indicators worked correctly after that.

I had already corrected bad grounds at the taillights when I did that trouble shooting, so I don't know whether bad grounds in the rear would cause the same issue.

Even after squinting at the wiring diagram for a long time, I can't say that I understand WHY this issue occurs when the headlights are on and the ground at the front turn signal lamp bulb is disconnected, but in my truck that was definitely the case. I used test leads from the turn signal bulb housings to ground, connecting and disconnecting them and replicating/solving the problem reliably in the ungrounded/grounded state. Lack of ground on either side always made the indicator light on that side come on when the headlight is on. I don't know if this is a peculiarity of the circuitry as designed, or whether some break/fault/short elsewhere in the system, perhaps in the dash cluster as you were wondering, lets juice to the headlights ground through the indicator circuit if they lack a better ground? Maybe a wiser head at electronics can enlighten us as to why it happens! Anyway, what you describe makes me suspect that your turn signal lamp housings at the front of the vehicle just need a good scrub down.

The other issue with the high beam indicator coming on incorrectly, I have not encountered. But I will say that when I got my '69, half the lights on it didn't work right , but aside from correcting a wiring polarity switcharoo the PO had committed, and replacing a flasher unit and a couple of burned-out bulbs, all the other electrical problems in the lighting eventually turned out to be bad/dirty grounds. Things get crusty after a few decades I guess.

-Will

[Classics Fan]

My electrical aptitude is best described as adequate so long as the problem is not overly complicated. The problem you describe about your dash signal indicators traced to a problem with grounds reinforces in my mind that my problems lie in a grounding issue somewhere as well. Given the multiple problems I’m having, and how they would all be temporarily rectified with a rap or two on the panel, further leads me to the conclusion it lies somewhere in the panel. I have a busy week or two ahead of me. My plan is to pull the panel as soon as I can make time and start by looking at all electrical connections. Thanks, Will, for your interest and reply.

[LockDoc]

-
Here is a pretty good thread on ground strap locations:

http://67-72chevytrucks.com/vboard/s...d.php?t=422234
.

[Classics Fan]

Appreciated, LockDoc!

[LockDoc]

Originally Posted by Classics Fan

Appreciated, LockDoc!

No problem.
.

[dmjlambert]

Here some additional hints and tips about the instrument cluster. By looking at the wiring diagram and studying the printed circuit and how it is attached, and looking at various forum posts, you will find the ground connects to the instrument cluster by a black wire in the connector plug. The other side of that back wire goes to a clip that pinches the sheet metal in the instrument cluster opening in the dash. You can use alligator clip test wires to add a more reliable ground connection on clean metal to see if that wire is a problem.

There are a couple places on the printed circuit where a screw goes right through the printed circuit trace and screws into the metal of the housing. That forms an electrical connection. The trace for ground is not complete from one side of the printed circuit to the other side without having a good connection through those screws and into the metal housing. You can polish the printed circuit traces where they are exposed to the underside of the screws and to the connector plug, I use some Brasso on a Q-Tip to do that. Make sure the underside of the screws are nice clean metal. The screws that make that circuit are right next to the connector plug and right next to the high beam indicator lamp.

Couple of threads that may be useful:
https://67-72chevytrucks.com/vboard/...d.php?t=709847
https://www.67-72chevytrucks.com/vbo...11#post8605411
I have experience with the gauge cluster and don't know much about warning light cluster, and I don't think you mentioned which you have.

[Classics Fan]

Appreciate all the information, dmjlbert. My cluster is gauges not warning lights. With all the tips, hints and information shared on this thread I feel confident I’ll find and correct my problems. I’ll post back with results and/or any more questions after I dig into it.

[Rick Bollinger]

There is two screws on the back going through your printed circuit that will cause most of what your issues are. It is a ground and can be reached while the cluster is in place. Just loosen and re tighten a few times to get a good contact. You must be careful not to tear your printed circuit when you tighten it up so don't go crazy with it. These screws go through the ground circuit and ground the pan to the circuit. I spent days cleaning connections and bulb sockets with no luck until I found this.

[Rick Bollinger]

Just an add to post If you use a meter to check the ground on the screws it will show a ground. But it is not making contact to the copper strip in the printed circuit where it needs to have ground. The ground comes through the bottom of the screws to the top of copper strip

[Classics Fan]

More good info, Rick. I’ll do the due diligence to ID the ground screws and see if I can access them without removing the panel. My truck has AC so space is at a premium. So far I haven’t figured out how to even reach the top of the headlight switch to depress the keeper button to remove the switch rod without removing some AC ducting but that’s a minor complication. Thanks for your post!

[Rick Bollinger]

Mine also has AC. And was doing the exact same thing as yours. I even had a new printed circuit in mine and not making contact.

[Classics Fan]

That’s encouraging to hear (corrected an identical problem). I want to avoid buying a new $70 printed circuit if it can be avoided.

[dmjlambert]

I don't think they are that expensive, and as with almost all parts often times you are better off getting a new-to-you used part. If you're a premium member here you can post want-to-buy ads, that is usually what I do. But Manes Truck Parts also has used parts such as printed circuits. If you examine your printed circuit, test it for continuity, and make any necessary repairs it will most likely be fine. I had a couple of traces that were delaminating from the plastic, and I glued them back down and it's been fine for several years now.

[Classics Fan]

So to close this thread: today I pulled the panel, replaced all the original incandescent bulbs with new LEDs, and made sure the two ground screws on the printed circuit were clean and tight. There is a ground wire from the back of the panel to the metal dash. One end looked suspect so I replaced that. The end result when everything was put back together is a brightly lit panel that functions as it should. Thanks to everyone who contributed with suggestions on what to look for!

[custom10nut]

Originally Posted by Classics Fan

So to close this thread: today I pulled the panel, replaced all the original incandescent bulbs with new LEDs, and made sure the two ground screws on the printed circuit were clean and tight. There is a ground wire from the back of the panel to the metal dash. One end looked suspect so I replaced that. The end result when everything was put back together is a brightly lit panel that functions as it should. Thanks to everyone who contributed with suggestions on what to look for!

Grounds, grounds, and more grounds.
These trucks a very dependent on ample grounding.
Your issue with Ted ash lighting is a common one,
The issue is that the dash panel is plastic.
On the advice of other members, I ran multiple (four, I think) grounds from the back of the panel to the steel dash.
Also attach multiple extra ground straps from the body to your frame.
This is the only was to fix the electrical issue

[HO455]

Good work! And thanks for posting your results. You should reward yourself with a frosty beverage.

[Classics Fan]

Originally Posted by HO455

Good work! And thanks for posting your results. You should reward yourself with a frosty beverage.

Done!