Blue Dingy Thingy

Blue Dingy Thingy

I do not recommend people discard the chime box. Doing this has come back to haunt people. While you may be a careful driver, other people often aren’t. With the exception of the seat belt chime, which I find insulting as well as annoying, I recommend all other functions be kept intact, especially the hand brake and headlight warnings.

  • The dash lights can be obscured by hand and steering wheel position or the light may be out. The audible brake warning provides additional driver notification. Yes, people have driven around with the hand brake on even with the light glowing, which usually results in major rear brake work.
  • It is a common practice in Fiero to disable the headlight motors in winter to prevent damage to the lift system. The headlight switch provides little visual feed back that it’s on. This makes it really easy to leave the lights on after driving in dreary weather unless the chime unit is working. (It’s not perfect… if the dash dimmer is off/broken the chime won’t alert for the headlights.)
  • The key warning is a toss up. If you want to disable this so you can work in piece, put a switch in the control line for that function. Even an experienced driver will leave the keys in the switch at times. (Of course this only matters if the switch in the steering column works… Many of them don’t.)

There are 2 reasons people need to mess with the chime wires. The first is to find the source of a problem the second is to customize a function. Custom function can be as simple as disabling a tone or replacing a tone with a new signal. The most common problem is “random tone” which is extremely annoying. Random Tone is the occurrence of one or two tones at random times. Since it usually doesn’t have any repeatable pattern it’s a royal pain to trace.

The most accurate list of chime contacts I’ve found is here-> Fiero Tech Zone He’s got good pictures too. There is another list at Michigan Fiero Club but it’s not right for any of the cars I’ve looked at. (In their defense MFC does have a number of other articles that are good.)

The best way I’ve found to alter the function of the box is to remove terminals from the socket. This is a fairly simple process. I do not recommend cutting the wires. The main reason is you may want to return the box to stock operation if you sell the car. The other is that in my case I was mainly trying to determine what line is the source of the “random ding” problem that’s been driving a bunch of people, including me, nuts. This way if the line I disable doesn’t solve the problem I can put it back and try another with no splicing.


This is likely the last update this article will receive as I have stopped all work on the chime box. Chime boxes are still available thru GM and AC Delco. (The part information is at the end of this article.) While at one point I did look into repairing them, it simply isn’t cost effective to offer that service. Millions of GM vehicles from 1882 -1996 used the boxes and new ones can be found at decent prices thru parts stores that carry AC Delco.

The front of the socket is the side the chime plugs into. I’m making sure we’re all on the same page since the “Front” is pointing to the right in some cars and down in others.

There is a manufacturing defect in the chime box. See the Defect Report about it farther down. At this time I believe this defect is the cause of random tones, chimes that sound like they have static, and most weak or dead chime units.

Disable a function without cutting wire.

First drop the socket off its bracket on the heating system. The ones that face right are held in place by 2 screws. The ones that face down are held by one screw and the other side is sort of wedged onto an ear on the bracket. Let the whole thing hang by the wires. Now you’ll be able to get to both sides of the socket easily.

Next remove the white plastic clip on the back of the socket. There’s one clip for the chime and another for the horn relay and hazard flasher. The clip slides out the side of the socket. (You only need the chime clip out.)

Look at the clip. Notice that one prong has a notched end. This side of the clip goes into the hole on the hazard socket side of the chime connector.

Look at the front side of the socket. Notice how each terminal opening is notched on one side. To remove the individual terminals slip a small wire or screwdriver into the notch. That will release the tab that holds each terminal. You may have to wiggle or pry your release tool a bit just be careful not to damage anything.

When inserting a terminal make sure it goes in the way it came out or it won’t lock and you won’t be able to insert the retaining clip.

When you’re finished playing with terminals put the clip back into the socket. The clip gives added support to the terminals so they can’t pop out when you plug in the chime.

That’s about it for the thermals.

Chime “logic”

The Chime unit has 5 functions listed in the table below. The remaining terminals are Main Power, Ground, and a line that is tied to the ignition switch Run circuit to tell the box if the car is on or off so that it knows which functions are relevant. (Remember, there are 5 key positions ACC, Lock, Off, Run, and Start.)


Key Position

Function Controlled by

Key in Switch Warn

ACC, Lock, Off

Switches in steering column and A post

Park/Head Light Warn

ACC, Lock, Off

Tied to dash backlighting.

Brake Warn


Switches in parking brake handle and combination valve

Seatbelt Light


Always on for 10 Seconds after key on

Seatbelt Tone


Like above but only if driver’s belt not latched. Switch in the belt retractor.

The functions controlled by switches are all activated when the switches close a path to ground.

The seatbelt warning timer is part of the chime box. The seatbelt light will always activate for about 10 seconds when the key is turned to the run position. The seatbelt chime will activate at the same time only if the driver is not belted. The driver’s belt latch has a switch in it to detect that the belt is buckled. Fiero’s wiring doesn’t monitor the passenger seatbelt.

If the seatbelt sense line (line H) is removed from the chime socket then the seatbelt chime will never sound. The seatbelt light will still activate each time the key is turned to run.

If the Chime box is unplugged the seatbelt lamp will not light even in Lamp Test.

DO NOT depend on the chime to tell you the key is in the ignition switch! The contacts of the key sensor in the steering column can get out of adjustment resulting in unreliable operation of the chime. Some key cut patterns can also cause intermittent contact of the key sensor. Wear in the ignition lock can also be an issue with this. Fixing the key sensor or ignition lock is possible but requires tearing apart the steering column.

If the dimmer for the dash lights is off then you will not get a chime if you leave the park/head lights on when you shut off the car. This is how GM chose to wire it. The only reason I can think of is when you have to leave the parking lights on. This way you can kill the chime while you pump gas or work in/around the car. (It doesn’t kill the key buzzer. If the door is open with the key in, the chime will still ring.)

I don’t see any reason to change it but one possibility is to run a new wire from the parking light terminal on the headlight switch to the chime. Not exactly easy but it would make sure the chime always activates.

The Random Tone Problem

Note: This section has been left in only for historical value. If you are having this problem read the Defect Report farther down this page first.

As I said above this is annoying as hell. Hearing a chime out of nowhere for no reason really gets on your nerves, especially if it happens several times during a short trip. The simple fix of pulling the chime isn’t good because it disables everything. For those of us that lock the headlights up in bad weather this can be a problem because the switch doesn’t give you much of a visual clue that it’s on. It looks pretty much the same on or off.

The current definition of the Random Tone problem is 1 or 2 tones sounding at random intervals. The interval can be a few minutes or days. There has been no evidence of the pattern being repeatable. No one has reported seeing any of the dash warning lights active when this occurs. In my testing it does not appear to be related to the hand brake switch since the tones still occur with the switch disconnected. It doesn’t seem to be the chime box itself since replacement of the box doesn’t fix the problem.

That I can tell there are only 2 signal lines that should cause this, all the other functions seem to be disabled when the key is in the on position. The seatbelt line could do this if there is a problem with the seatbelt timer. The other is the brake warning circuit. Problems with the hand brake switch or the wiring could cause random tones but not pass enough juice to light the warning lamp

Determining the problem line becomes a process of elimination. Unplug the control terminals one at a time until the problem stops.

Once you figure out what line is the problem you need to decide what you are going to do to fix it. You have 2 choices. Trace the circuit looking for problems or leave the terminal for that line unplugged. I can’t give you much other answer than that because tracing the circuits is allot of work even if you know where they all go but leaving a chime dead presents other problems, like people too stupid to look at the dash and see the brake warning light is on and check the hand brake. If the chime is also screaming at them the light is a little harder to ignore.

Defect Report


It has come to my attention that there are 2(TWO) versions of chime box! At this time the 2 boxes appear functionally identical and they should be interchangeable. The GM part #’s are printed on the box but may have faded off.

The Old style one has square corners and a door that opens to expose the whole back of the chime board. It is unknown at this time what if any defects apply to the old style box. If you have problems with this version, replace it with the new one. (The GM part # for this box is 10024379. I don’t believe this unit is still available anywhere.)

The New style has rounded corners and a door that opens on the small end opposite the terminals. (It is pictured in the Fiero Tech Zone pictures.) It is the new style box that has the defect. (The GM part # for this box is 10037040 and is still available thru some dealers.)

The Chime box has a minor manufacturing defect, which can make the box appear dead, cause weak chime sounds, cause chimes that come and go, and random chime. This problem is easily corrected.

If you wiggle or squeeze the box and it affects the chime sounds then you likely have this problem. This problem can be aggravated by vibration and by handling the box.

The problem is the metal “bridge” that supports the chime disk on the circuit board. This bridge is being used to make electrical connections on the board. The end of the bridge closest the terminal end of the board is not soldered well because of an incomplete circuit trace. This poor joint cracks and screws up the chime. Note that this joint can be cracked with little visual evidence.

View Picture of defect area. (Large Image, 138K.)

Reworking this connection should help cure most if not all the problems. You will need a soldering iron/gun in about the 100watt range. You need to heat the area quickly or you’ll lift the copper off the board. (Hold the iron on the bridge and let the solder carry the heat to the board.) Low wattage irons will have trouble heating the bridge quickly enough because of its mass and by the time the bridge heats enough the trace is too hot and will likely be damaged. If the trace is not firmly attached to the board then likely the board will fail again in the near future. Do not bridge solder to any adjacent terminals.

This problem likely affects a very large number of chime boxes. It is caused by poor design on the circuit board and use of high speed soldering machines to assemble it. The bulk soldering equipment used to make the board commonly has problems if the eyelets of the copper traces are not a closed loop. In this case there isn’t enough room to close the eye and keep enough space between other traces. (If traces are too close the solder will bridge the gap and make a short circuit.)

Because of the nature of this problem don’t be surprised if new or used replacement boxes have the same problem. New boxes may work when you first get them and die in short order. To prevent this problem avoid handling the chime box by the large faces.

How was this problem found?

Several Chime boxes were tried in order to eliminate the random tone but none of them did the job. Some were better but the random tones where still there. In addition some boxes gave weak tones. Others were intermittent, one second you’d get a good strong chime and the next you could hardly hear the thing. (I’ve tried at least 5 boxes over the last year.)

Since multiple chime boxes have given similar results I suspected the socket or a damaged terminal. To eliminate this I removed the terminals from the socket one at a time and plugged all of them onto the chime board. While checking terminals I held the box by the large sides and the tones changed. When I let go of the box the tone changed again. Squeezed the box again and sure enough tones changed.

Since I knew all the terminals where good now I put them back into the socket and disassembled the box. I got the board out and looked for things that could move when the board was flexed. The most obvious things are the terminals and the chime support. Sure enough one end of the chime support was loose. Soldered that back in place and now the box works perfect.


The defect joint is part of the main ground circuit on the board. Just how bad problems caused by this joint cracking is hard to predict because there is more than one way for a crack to form. The box can appear dead, make really faint sounds, and half a dozen other things.

Why would the box make random tones if the joint cracks? The main reason I suspect is the seatbelt warning function. When power gets interrupted it can scramble the seatbelt circuit enough for it to let out a tone. If the power interrupts long enough then it can even make the seatbelt light come on until the timer runs out again. (The tone will also sound if the seatbelt isn’t buckled.)

Parts Sources

The new style chime unit, 10037040, is available thru some GM/Pontiac dealers and GM Parts Direct.


81 comments to Blue Dingy Thingy

You must be logged in to post a comment.