Dash/Instrument Illumination: Step by Step Search

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dibbons

dibbons

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Most all the on-line discussions about electrical glitches eventually end without the original poster ever resolving the problem and leaving the reader with the same/similar problem still without a solution. So my intention is to follow this thing through to the end.

Regarding the '65 Plymouth Valiant Signet convertible, I am beginning my search to uncover the problem with two of the dash lights (the one to the far right upper corner of the gauge pod is working fine, as well as the console shift indicator lamp). As far as I can tell, all three lamps use the same positive battery source via the fuse panel, head lamp switch, and finally circuit board. In other words, the dash lamp located directly below the turn signal indicator and the lamp for the speedo pod are out of commission for reasons unknown at this point.

I recently had removed the gauge cluster and replaced all of the mini-lamps in the cluster which are #158. I tested the lamps separately (loose) while in their little black plastic sockets using jumper wires and battery voltage. They worked during that "bench" test.

When the dash was installed, the two in question failed to work (along with a failure of the oil pressure warning lamp). Yesterday, I crawled under the dash and was able to remove the two instrument lamps and the oil pressure lamp. I bent the pair of little brass colored tabs in the plastic bases to insure better contact and replaced the lamps back behind the dash where I had removed them (a little tricky, but possible with a little determination). The brass was without any visible corrosion, but I did shine them up a little (they are very tiny little things). When I tested again, the oil pressure light came to life with the ignition "on''. The two dash lamps still failed.

When it got dark tonight, I crawled back underneath the dash (using a flashlight) and attached a wire with alligator clip ends to the screw that secures the circuit board to the instrument cluster on the speedo side, which just so happens to be right alongside one of the lamps that failed (and looks to me like it also provides a ground for that lamp). The other end I attached to several body ground points in the interior of the vehicle. However, this test effort was still not successful in coaxing any light from the two stubborn dash lamps. But that one lamp over above the gauge cluster still working like a champ and thumbing its nose at me time & time again. Grrrrrrrr ...

I also touched a wire to several of the heads of the four chrome Phillips screws that hold the instrument bezel to the dash frame and grounded the other end, but that did not help anything either. To be continued.

lamp 158.jpeg


65 inst cluster.jpeg
 
Are the bulb holders origional or new. Reason I ask is there are two sizes, both will fit but only one size will stay inplace.

Also there MIGHT be a crack in the cir board to the lights in question that is not allowing the lights to work.

If removing the dash again is posable that would make fixing the problem much easier.

Like removing the front seat to work under the dash. Seems like a PITA but makes the job SOOOOOO much easier.
 
You are overthinking this ............there are only basically 3 types of lamps hookups in the clusters
1...Dash illumination. These are the lamps that light up any instrument such as speedo, the shift quadrant, the radio dial (factory radio) and so on. They all have ONE voltage source, and here is how that works
.The headlight switch has TWO power sources.

A.... One is unfused, comes from the ammeter circuit, and goes direct to a breaker in/ on the light switch and powers ONLY the headlights, nothing else. That circuit is not part of this problem

B.... the other light switch power source comes from the tail light fuse/ circuit and powers the parking, tail, and instrument lamps. That power goes through the "park/ tail" section of the switch, into and out of the dash dimmer control, and then comes out on a TAN wire and goes TO the fuse panel where that now dimmer controlled power goes TO the INST fuse. FROM that fuse, all dimmer controlled lighting is distributed.

IF YOU HAVE an illumination lamp in the cluster that does not light, then the problem is right there at the cluster. Either one of the harness connector pin/ terminals, or a loos pin on the circuit board(s) (some clusters use two boards) or a dirty copper area on the board where the lamp socket contacts. Weak/ corroded socket, or bad lamp or corroded lamp terminals.

2...OTHER TYPES OF lamps. These are fed separately. The headlight "bright", the turn indicators are all grounded, just like the illumination lamps These are all fed independently from each circuit in question.

3...WARNING LAMPS. A warning lamp such as OIL pressure IS NOT GROUNDED. This type of lamp is fed full battery switched power from the "key" and then the low or ground leg goes to the sender such as oil sender. This sender provides a ground when the oil pressure is low
 
IF YOU CAN provide a good sized photo of the rear of your cluster it will help. I do not have a source for that other than "accidently" finding such a photo on the internet. As an example, my 67 originally had two separate in-line harness connectors feeding two boards to make up the complete cluster. This means that there is at least one lamp on both boards, so one feed path might be compromised.

1...Clean and solder the harness connector pins or obtain "repop" boards. Use a good "electronic" solder and buy yourself some liquid flux which matches. "Flux pens" are a good option.
2....Loosen/ tighten the gauge nuts as they get corroded and lose contact with the board.
3...You are on your own on the gauge regulator/ limiter as I'm not familiar with early clusters
4....Get an abrasive eraser or maybe even very fine sandpaper, perhaps 500 or 1000 grit to clean the board contacts around the socket holes.
5....Clean the socket contacts or replace them, along with the bulbs I would suspect corrosion in this area, board to socket, socket to bulb, and amount of pressure at the contacts. Bend them "spring" to make them tighter contact
6....Clusters are notorious for poor grounding. Make sure boards are grounded to the cluster and add a grounding pigtail which you bolt to the dash frame or column support. Again, if you have two boards, make sure the pigtail grounds both
 
I'd pull the cluster and do the bench testing with everything in place. That way you eliminate the circuit board and sockets as the problem. Use the cannon plug pins (make sure they're not loose) and the housing ground(s) as your test points. You can also test the sockets in the cannon plug for the correct supply juice too.
 
67Dart273 said:
IF YOU HAVE an illumination lamp in the cluster that does not light, then the problem is right there at the cluster. Either one of the harness connector pin/ terminals, or a loos pin on the circuit board(s) (some clusters use two boards) or a dirty copper area on the board where the lamp socket contacts. Weak/ corroded socket, or bad lamp or corroded lamp terminals.
Click to expand...

OK, I made two more tests: A) Turned the head lamp switch to "parking light" position and crawled underneath to wiggle the dash light closest to the driver's door. Result: nothing doing. B) Removed the bulb/socket in test number "A" above and swapped it with the turn signal indicator bulb/socket. Result: The turn signal indicator functions with either mini-lamp/socket and the dash light nearest the door does not work with either one.

Conclusion: I don't see any other way to place the blame for the dash light problem except for it being a defect of some sort with the circuit board. To be continued.

We still need to see if the coolant temp and fuel gauge are working-those I did bench test and they both worked outside the vehicle. Ammeter works OK.
 
It could very well be a break/ crack in the board. But you can fix that, easily. That is, if you can solder. As I said for this type work, and really, ANY automotive soldering, you should not only have "the usual" --a good iron or gun, and "radio" type solder, but you should have some liquid made for electrical soldering flux. THE PASTE you buy at plumbing and other places is ACID, do not use it. And you may not need it.

You can scrape places clean say, every couple inches and move your ohmeter along the trace to find a break. Then just solder a wire jumper across the break, or across the whole trace.

I agree with cudamark---bench test it. Get your wiring diagram and identify and mark the switched key power going to the board, and make a note paper of the connector pins. You can jumper power to such as the turn or high beam indicators, the gauges, use resistors as senders to check the gauges, everything.
 
I don’t know about early A’s but there are three or four separate grounds on the cluster on my 69. They are grounded to the pot metal housing by screws. If they are all not grounded good, some of the lights won’t work. Sometimes there is corrosion where the screw touches the circuit board.
 
Mike69cuda said:
I don’t know about early A’s but there are three or four separate grounds on the cluster on my 69. They are grounded to the pot metal housing by screws. If they are all not grounded good, some of the lights won’t work. Sometimes there is corrosion where the screw touches the circuit board.
Click to expand...
Yet one more reason to mock it up on the bench
 
Dash issues can definitely drive you crazy. I did exactly what Del said. Tested everything on the bench. I soldered all the pins to the board and put star washers under all the screws. A pencil eraser cleans up copper board traces nicely.

A old computer power supply makes a great 5 & 12 volt supply to provide battery power & gauge power. Used ones are easy to come by, often free, or a few dollars. Lots of YouTube videos how to do it. They are pretty high powered so use a fuse.
 
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