Idiot Lights

[kennerks1]

1976 Cadillac Eldorado - I have somehow lost all of my idiot lights (dashboard warning lights).  They are supposed to light up when starting the car and then extinguish.  They used to work and the bulbs are not all burned out (when you ground a sensor lead, the bulbs light up).  Any thoughts on a cause and/or remedy?

[Jeff Rosansky CLC #28373]

Sounds like you need to find where the cluster grounds and repair/clean the ground.  You could run a jumper ground, but if possible may be best to find the reason for the failure.
Jeff

[The Tassie Devil(le)]

Also, check for a burnt-out fuse.

Bruce.

[James Landi]

As long as each light glows when you ground them, then they are functioning.  The start position that causes them ALL to illuminate must employ a specific relay that "grounds" all of them for that instant when you're cranking, so if you have a wiring diagram, there has to be a relay that ONLY activates in the crank position.   In newer cars, many such functions are accomplished through multi-function generic electronic modules..If you have the tech manual, it should be relatively easy to find this problem.

[TJ Hopland]

I'm going from memory but I think there is a section or two of the ignition switch one grounds and the other is a +.  Those are sent to the instrument cluster which then has diodes to keep the various lights from back feeding each other.   A diode is like an electrical check valve, it only allows the flow to go one way so you can have something like a single ground for several lights for something like the test mode but they can still be independent for the individual sensors.   

I don't know for sure that a 76 was that way but I know it was done that way.   The module also sounds familiar, I can kinda picture that on the slightly later plastic clusters that had the membrane instead of individual wires.    Or did the membrane thing start in 74?

[kennerks1]

Fuses are all good - removed fuse panel to see if something was amiss on the back side - all is good.  Looked at the wiring diagram and don't see a relay anywhere in any of these circuits.  I do see what looks like a bulkhead connector, but am not sure where it is on the car. Thee idiot lights are not part of the instrument cluster, as best I can tell.  Still stumped.  We did replace a melted floor high beam switch, but I don't see how that could be related to this problem.

Paul

[dplotkin]

"We did replace a melted floor high beam switch, but I don't see how that could be related to this problem."

Here's how. The high beam indicator is one of those indicator lights that don't work. Melted wires and electrical failure are most probably related.

Dan

[James Landi]

Hi Paul,

Trying to be helpful here, so what Dan suggests may be related to the problem, and he might have nailed the issue; however, if you're still in the weeds and frustrated here are some thoughts.  GM electrics are often very hard to figure out as a circuit that you're looking for, which is a momentary ground through the diode set that was described above is hard to track down without an electrical "trouble shooter tree" that was part of tech manuals.  Assuming what you suggest-- that all of these constituent parts are visible, one approach would have you attempt to activate all the idiot lights simultaneously without cranking the engine.  You would use a continuity 12volt light, attach one lead to metal ground, and then probe the idiot light panel for the potential ground that would cause all of them to turn on.  You would have some indication that you have the correct single common ground connection when your probe light goes on.  IF and only IF you've convinced yourself that you have good cause to believe you've tracked down the common ground, then I'd use a five amp fused jumper where you used the probe. EIther the fuse will blow (because you've shorted a positive feed to ground) or  ALL the lights should glow and you now know you have the common, its color, and you might be able to trace that wire.  (or, you if you're anything like me, you can hook up a momentary push button under the dash, that would function for you to check the lights at your convenience.   (this advice comes to you from Mr. SHade Tree Mechanic and subject to review by more informed members)

[dplotkin]

I agree. I would first sit down in a comfortable chair with the wiring diagram and study all of the warning light circuits. Follow the high-beam indicator lamp wiring and determine how the high/low beam switch is related to it, and where, giving you the clue you need. Works for me nearly every time.

Dan

["Cadillac Kid" Greg Surfas 15364]

Paul,
What happens when you turn the key on?  Do any of the lights such as the Generator, Oil pressure, brakes. or seat belt light up?
Greg Surfas

[James Landi]

Greg brings up an excellent point... I think the "gen" light has to go on, because if it DOESN'T, then the alternator field is not activated, and the alternator will effectively be out of service-- and you battery will wear down quickly.  So, it's important, as Greg suggests ,to find out if any of these lights glow... the "gen" and brights and seatbelts should, I think, be lighting now.  If not, that's an important... serious... concern

[kennerks1]

OK, finally got the Eldorado and the service manual out of the shop (replaced leaking rebuilt non-original water pump and off center installed thermostat - how did they ever get that sealed?).
Did a little poking around:  Cadillac calls idiot lights "telltale lamps."  The shop manual does provide a diagnosis tree for each light - after some preliminary poking around, looks like I need to take the dash apart (which I have done before and is a PITA) to start tracing wiring and to check voltages.
There are 12 locations for telltale lamps on the top of the dash - my car should have 8 of them (washer fluid, seat belts, engine temp, coolant temp, oil pressure, generator, trunk open and brakes).  And not have: security system, fuel economy green, fuel economy amber and air cushion restraint (air bags ?). 
Of these 8, exactly one works:  brakes.  It works to show parking brake is on and flashes on when car is started. 
All others: nothing in any mode.
When you turn the key on, the brake telltale lamp lights and the buzzer sounds.
High beam floor switch works and high beam light in the instrument cluster lights.  All other interior and exterior lights work properly.  Fuse (5 AMP) for telltale lamps (and all other fuses) is/are good.
Paul

[TJ Hopland]

Does the diagram show that the 'lamp check' signal from the ignition switch is the same as the one that feeds the brake light is the same as the others that don't work?    I know that stuff got pretty complicated and seemed to change year to year.   One wire off under the seat can mess it all up because the seatbelts are tied to the brakes are tied to the parking brake to the park neutral switch to the buzzer to the door lights to the knee bone to the leg bone and I'm my own grandpa.   I don't have a 76 manual so I don't want to confuse things by looking at a 75 or 77 manual that may be different in some critical way. 

[kennerks1]

Back again.  Dash is apart and clock is out for overhaul.  Idiot light/telltale lamp problem persists.  I should have seven working (washer fluid, seat belts, engine temp, coolant temp, oil pressure, generator and brake).  The brake light works (put on parking brake and brake telltale lamp lights).  Short the engine (metal) temp light to ground and the buzzer sounds, but no light.  All light bulbs have been removed and tested - all are working.  The other 5 - nothing.  I am beginning to think the printed circuit film is kaput?  Can't get to the film or the multi connector without significantly more disassembly.  If it comes to that, I will probably pack it in.

[James Landi]

Paul,

THere may be "a way" around this... each of the tell-tale lamps connects through a sensor to ground.  Once you determine which "side" of EVERY lamp is fed by 12 volt, (I would guess that would be the brass/metal outside) and if all the lamps a mounted and electrically connected that way... you might consider tracing that common positive and simply cutting that wire.  At that point, simple ten dollar relay hooked into your ignition switch would provide you with tale tails when ignition is on. And a push button on the dash could provide you with a "manual test" mode.  Just a thought.  James

[kennerks1]

I hereby nominate myself for the title of dumbass of the week (or maybe the month).  As noted, took the dash apart over the weekend, with no result.  Poking around the dash innards this morning and what do you know - idiot lights!  Seems the central printed circuit connector was not properly seated.  Seating it properly, we get seat belts, oil pressure, generator and brake.  No joy on engine metal temp (buzzer only - no lamp) and low washer fluid.  The coolant temp lamp has been disconnected in favor of a temp gauge.  As long as I have a buzzer (and a coolant temp gauge), I can monitor engine overheating.  I will probably survive even if the washer fluid runs out without warning.
Sometimes it really is the simple solution.

[James Landi]

As the great Bard would say,  "All's well that ends well."

[kennerks1]

It gets even better. Pulled the service manual out and went through the steps for washer fluid (key on, wipers wiping, press washer button and pull float unit out of tank) - low fluid light works.  And, I discovered that the driver door must be open (why ?) for the engine temp light to light - it does!  We are now 100% on idiot lights/telltale lamps.  Life is good.

[mgbeda]

That engine temp light should still come on with the buzzer if you ground the switch at the back of the engine.

They did use the engine temp light and buzzer also as the key-in-ignition warning.  (Who knows why)  And often the key-in-ignition sensor gets worn and might always think a key is in there.  That buzzer/light only comes on when the driver's door is open.

-mB

[bcroe]

That engine temp light should still come on with the
buzzer if you ground the switch at the back of the engine.

They did use the engine temp light and buzzer also as the key-in-ignition warning.  (Who knows why)  And often the key-in-ignition sensor gets worn and might always think a key is in there.  That buzzer/light only comes on when the driver's door is open.    -mB 

Well yea the key buzzer is supposed to only work with the door open.  Here people have
been known to get out the other side, so that door has a second contact to also do it. 

The electronic alternator doesn't come on immediately if the GEN lamp doesn't supply
some power.  But the alt will get started anyway if you rev the engine (the way I do
on an entrance ramp).  Found that out when a hot A/C clutch bearing melted some
wires and blew the fuse 5 states from home, made it anyway.  Bruce Roe