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56 Dash Indicator Light and Gauge Wiring Issue

Started by stzomah, May 08, 2020, 03:50:43 PM

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stzomah

I have a 56 coupe that had an intermittent operating temperature gauge.  I restored the original one a few years ago but it did not work.  I recently bought an instrument cluster and pulled the temp gauge to replace mine.  I took my dash apart and pulled the cluster out far enough to replace the gauge using a mirror and shore blade screwdriver.  It was a challenge and I pulled the cluster around quite a bit during the ordeal.  When I put it together and started the car, the regulator light lit up dimly.  The new/old gauge worked but it read a bit high.  I reached behind and pulled the pink wire off and the regulator light went out.  I am figuring that I have a semi shorted coil in the gauge.  As I began to fish around to check everything, I pulled on the emergency brake and the gen light lit brightly and the gas and temp gauges dropped half scale.  I pulled the E brake tan wire from the switch and put a fluke on it measuring resistance to ground.  As I pulled the bulb socket around the meter went crazy.  It looks like there is a bad wire in the loom.
With all this happening at once, I’m a bit flustered:
•   Is the Gauge bad (shorted)?  But even disconnected the E brake will make the Gen light go bright and pull the gauges down.
•   Did I disturb the harness wiring and cause a bad wire connection.  Possibly shorting one of the pink 12v wires?
•   Did the generator or regulator just decide to go south.  I measured the voltage at the battery while at idle and I’m getting 13.2 volts.  I use a battery cutout and wondered if I need to re-polarize the regulator since I took voltage off it?  I’m reading about 10 volts at the pink lead on the temp gauge (disconnected at the gauge).  Am I getting enough voltage at the dash?
Has anyone had similar issued with their 54-56?
I attached the schematic with some highlighting..
1956 Series 62 Coupe
owned since 1975

J. Gomez

Wayne,

Hmm I knew I recognize the diagram you posted, I compile it and uploaded at the old Mid-Century site.   ;)

Quote from: stzomah on May 08, 2020, 03:50:43 PM
•   Is the Gauge bad (shorted)?  But even disconnected the E brake will make the Gen light go bright and pull the gauges down.

I do not think so but the gauges do required the cluster to be properly grounded and they will read erratically if there is a poor connection. Unfortunately the only source for it is via the four attaching screws. You can clip a wire to a good ground source to the cluster and see if anything changes.


Quote from: stzomah on May 08, 2020, 03:50:43 PM
•   Did I disturb the harness wiring and cause a bad wire connection.  Possibly shorting one of the pink 12v wires?

It is all possible that when you pull the cluster out the bulk of the wire hardness got stretched and wires may had loosen up.  With the age and the way the hardness is twisted in the area anything is possible. However I’m not sure there is a short but … ???

Quote from: stzomah on May 08, 2020, 03:50:43 PM
•   Did the generator or regulator just decide to go south.  I measured the voltage at the battery while at idle and I’m getting 13.2 volts.  I use a battery cutout and wondered if I need to re-polarize the regulator since I took voltage off it?  I’m reading about 10 volts at the pink lead on the temp gauge (disconnected at the gauge).  Am I getting enough voltage at the dash?

Do not think your gen and/or VR is bad on this case. However anytime you disconnect the battery you must re-polarize the generator (the VR does not required to be polarized, since sometime the polarization is done on the VR it is also assume the VR also gets the same treatment).

If you read 10 volts at the pink wire at the cluster which is the main feed for all of the items you are having issues with that wire is feed from the ignition switch. Although the ignition switch wiring is not near the cluster the wires to it goes up on the main hardness which is behind the cluster.

From memory when I did my rewiring the pink wires are all bundle together and solder and taped inside the hardness so the connections should be fine but like with age everything can go hay-wire.

I hate to say but if you do not want to pull the cluster all the way out to start troubleshooting your gremlins one alternative is to pull the dash pad. It is a bit more work but it would give you clear access to everything around the dash. Check the Service Manual under section 14 to remove the pad.

Good luck..!
J. Gomez
CLC #23082

stzomah

Hi Jose,

Yes, plagiary is a sign of flattery!  Having good internet searching skills is a must for old car enthusiasts...  I figure the only common wires to all of those items is the pink 12v wiring.  I ordered some 18ga high temp GXL wire in 10 colors.  I will make a new pink "buss" and tie into it at the load side of the fuse.  I'm thinking that original large solder joint may be failing and i'll just replace that whole feed.  I found a source for the 2 wire 5/8" bulb sockets (fits fords and corvettes circa 63-76).  Found for $12.99 each on ebay.  I have a spare instrument cluster i will use to fabricate the new "pink buss" in the shop.  I'll solder all the connections and use heat shrink.

I too was wondering about the "ACC" connection on the ignition switch.  The wiring appears to be solid on the switch.  I'll trace as much as i can but when i restored the dashboard a few years ago, i redid all of the harness wrap.  Looked real good when i was done :).

I have the dash top off and disconnected most of the cluster.  I had to disconnect: left vent cable, speedo cable, and the trip reset cable.  I dropped the steering column a inch to pull out the painted column cover so i did not scratch it.  I used the beauty mirror from the sun visor to reach the 2 blade screws for the temp gauge.  It was very tedious and took over an hour for both screws.  All that to find that i now have a wiring problem.  Very disappointing but i'll get it..

I'll report back in a week to two.  Shipping is slow on the items i bought..

Thanks
Wayne
1956 Series 62 Coupe
owned since 1975

cadman56

Jose is correct.  I feel your pain.  It is am absolute nightmare under the dash.

I  worked under the dash of 4 56's  and  made 2 complete new harnesses front to back.
That pink wire, in my estimation, is powering too many things.

As a side note to all at this point, one thing one can get from dismantling a 56 is all the plastic wire ends and connectors.  The more you can get the better off you are if you do have to make a new harness.
1956 Cadillac Coupe deVille (sold)
1956 Cadillac Convertible (sold)
1956 Cadillac Eldorado Seville (sold)
1967 Cadillac Eldorado (sold)
1968 Cadillac Convertible (Sold)
1991 Cadillac Fleetwood Brougham dElegance
Larry Blanchard CLC #5820

stzomah

This is what I found today.  Reading the shop manual section 13 and looking at the schematics, I started to follow the pink circuit more closely.  I wondered if 12V was interrupted (break in the pink power wire) to all 5 items (3 lights and 2 gauges) how could it get power?  I read the operation of the GEN light circuit.  It is wired through the light bulb to the regulator.  If the regulator is putting out 12V or more, the circuit current will not flow and the light will remain out.  It is a type of voltage differential circuit.  The voltage/current will not flow to the bulb unless there is a difference between the brown (regulator) wire and the pink 12V wire.  It dawned on me that the fuse was blown in the INSTR circuit (pink).  The voltage for all 5 items now was being back fed from the regulator through the GEN bulb (hence the 10V-2V drop i was reading on the pink wire).  When i grounded the BRAKE light by pulling the handle, it created such a voltage drop that the gauges dropped 1/2 scale and the GEN light went full bright.

As intuitive as it may seem now, i did not check the INSTR fuse.  Since I was getting voltage at the pink wire (albeit 10V) I believed it to be intact.  It was not..  I must have shorted the circuit while installing the gauge.

This was so confusing since i was getting power but when i pulled that parking BRAKE, everything went haywire...  It was as simple as a blown fuse but normally a blown fuse would indicate no voltage to the circuit.  This was a bit tricky!

One last observation that also had me confounded...  These lights should illuminate when you turn the ignition switch 1 spot (ON) to the right to check for blown bulbs.  You should also see the temp and gas gauges jump to the low position.  That was not happening and had be scratching my head.  It made sense that if the GEN differential circuit was not putting power out, there was not voltage until the engine started and the generator was charging.

I don't have the correct fuse so i now have to wait to get one.  After i can close everything up, i'll give a final report..
1956 Series 62 Coupe
owned since 1975

J. Gomez

Quote from: stzomah on May 14, 2020, 01:52:19 PM
This is what I found today.  Reading the shop manual section 13 and looking at the schematics, I started to follow the pink circuit more closely.  I wondered if 12V was interrupted (break in the pink power wire) to all 5 items (3 lights and 2 gauges) how could it get power?  I read the operation of the GEN light circuit.  It is wired through the light bulb to the regulator.  If the regulator is putting out 12V or more, the circuit current will not flow and the light will remain out.  It is a type of voltage differential circuit.  The voltage/current will not flow to the bulb unless there is a difference between the brown (regulator) wire and the pink 12V wire.  It dawned on me that the fuse was blown in the INSTR circuit (pink).  The voltage for all 5 items now was being back fed from the regulator through the GEN bulb (hence the 10V-2V drop i was reading on the pink wire).  When i grounded the BRAKE light by pulling the handle, it created such a voltage drop that the gauges dropped 1/2 scale and the GEN light went full bright.

As intuitive as it may seem now, i did not check the INSTR fuse.  Since I was getting voltage at the pink wire (albeit 10V) I believed it to be intact.  It was not..  I must have shorted the circuit while installing the gauge.

This was so confusing since i was getting power but when i pulled that parking BRAKE, everything went haywire...  It was as simple as a blown fuse but normally a blown fuse would indicate no voltage to the circuit.  This was a bit tricky!

One last observation that also had me confounded...  These lights should illuminate when you turn the ignition switch 1 spot (ON) to the right to check for blown bulbs.  You should also see the temp and gas gauges jump to the low position.  That was not happening and had be scratching my head.  It made sense that if the GEN differential circuit was not putting power out, there was not voltage until the engine started and the generator was charging.

I don't have the correct fuse so i now have to wait to get one.  After i can close everything up, i'll give a final report..

Wayne,

Welcome to the “Electrical troubleshooting world” nightmare this is reason our alcohol pantry needs to be well stock.   ;D

You have encountered a “one in a million” condition  :o when things just do not add up, lucky guy..!   ;)

You are correct, the “GEN” light at the dash connects to the +12V source “pink” wire for +12V source and “brown” wire for the ground, “only” when the engine is running turning the generator you will see +12V at this wire. Since there are +12V at both ends of the bulb the light is extinguish under normal conditions.

As you may be aware in some situation with low RPMs if the VR is weak or the generator produces a bit less voltage than what the battery has you could see the “GEN” light flicker. Some folks have added a diode on the VR “brown” wire going to the light bulb to stop the annoying flickering.

In you case as you noted you are 110% correct, with the generator turning there would be +12V at the “brown” wire of the light. If there is no +12V at the main power source “pink” wire, the filament of the bulb would pass the (resistance) voltage over to the “pink” when there is no power on it (as in your case a blown fuse).

So when you pull the “E/B” handle placing a ground on the “brake light” the voltage drop considerably causing all kind of strange things with the gauges and other lights.

So just my personal views, IF one has a “diode” on the “brown” wire for the “GEN” light what you had experience with an open +12V source do to a blown fuse the same would not occurred since the diode would block the +12V going up to the light bulb, only the ground would go by. 

BUT again this is just one in a million so it may not be worth the hassle since is much better having extra drinks while troubleshooting electrical problems.   ;D
J. Gomez
CLC #23082

Paul

This is very interesting. I have a similar issue with my cluster on my 59 cdv. The gauges don’t really work correctly. I also get a dim gen light after a few mins of operation. Then it goes full bright. But it is not on when the key is in the ignition before engine cranking. However if I ground the temp sensor wire the generator light goes full on bright instantly. I suspect I may have a similar issue. I will need to create a better ground for the dash cluster but as far as a blown fuseâ€" where would I look for this? The fuse box seems to be intact? Are there other fuses somewhere I’m missing?
59 Caddy, Seminole Red with Dover White top