Burnt tachometer - Team Camaro Tech
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post #1 of 16 (permalink) Old Aug 6th, 18, 01:42 PM Thread Starter
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Burnt tachometer

Hi
I own a 67 Camaro with the RS option.
Now I have a electrical problem and I need some help.
Last Friday I had a terrific smoke in my car and I found a burnt resistor on my tachometer. As you can see on the attached picture. Well, I found the reason for the smoke, but the biggest question is, why is this resistor burnt?

What happens; as I said, last Friday I decide to take the Camaro for my drive to work early in the morning. I turn on the light and I haven't heard the noise of the RS headlight doors. So I stopped the car and saw, the doors are not open. The light was on. So I decide to open the doors by hand. No problem. I drove the car for around 20 minutes to my working place. Turn off the lights and bring the light doors into the closed position.
Later I took the car for lunch and start driving (without light on). After a short time I smell there is a problem and one minute later the gauges are fully with smoke. So I stopped the car immediately.
I have no idea why the doors are not working. I never had a problem with them.
What do non-functioning doors have to do with a burnt tachometer?
Is that a coincidence? I can't believe that.

For information, for a couple of months I installed a Petronix Ignition Ignitor III with a new Petronix Flame - Thrower coil. The car runs very nice and I never had a problem with the tachometer or something else. I don't think it's coming from them.

My wiring on the car is new and looks good.
A resistor can only burn if the current is too high or the voltage is too high.

The RS front light doors circuit is very complicate and there is also a diode in this circuit. I don't know what happens if the diode is defective?

Another incident I had: During a long drive with the car, I decide to switch on the headlight. Then I pulled the head light switch a little slowly. Then at a kind of a middle position of the switch, the ignition stops working and a big bang was coming out of the exhaust. An I recognize a misfire. But just for a short time. Since then I pull the head light switch very fast. No problem anymore. But this incident is the only thing to do with the light and the ignition.

The tachometer is connected with the pink wire from the ignition switch and from the brown wire from the coil. Where is the problem came from? From the pink wire or from the brown wire?

Has anyone an idea whats going on with my car? Where should I start searching?

Greetings from Switzerland
Daniel
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post #2 of 16 (permalink) Old Aug 6th, 18, 06:57 PM
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Re: Burnt tachometer

Well sounds like for you have some issues with your electrical system.
Lets start with the headlight doors - Daniel fill in the missing parts - Are these RS headlight original to the vehicle or aftermarket?
If original factory, have you checked the relays on the boards? If aftermarket, who makes them? Yes diode issues can keep doors closed or open but so can a defective floor headlight dimmer switch. If you turn on the headlights doors do not open, if you hit the high beam floor switch do the doors open?

Headlights have full power at the headlight switch and it sound like your switch is causing a dead short in certain positions and circumstances.
You say the wiring is new, is the switch? Is this a factory replacement harness or an "Update" using new style "blade" fuses or old school glass?

As to the tachometer the resistor does look like it took way too much voltage and cooked. Is the tachometer "new" reproduction?

Brian


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post #3 of 16 (permalink) Old Aug 6th, 18, 10:33 PM Thread Starter
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Re: Burnt tachometer

Hi Brian
Thank you for your answer.

The car is an original RS car. The RS doors, motors, switches and relais are looking like new, but installed like factory. I think no modification is done, just replace with new relais, new wiring, new switches and so on based on the original. All the parts are looking too good for such an old car. The car has the old school glas fuses. I think also the tachometer was replaced once with a new one. As you see on the picture, it looks very clean, abart from the burned section....
All these was replaced during a restoration more than 8 Years ago. I bought the car this way, and the previous owner has no idea.

I think I should start with the headlight doors. I will check the dimmer switch this evening and others. I'll check if the relays are activated or not. Where is the diode placed? I haven't found it.

I will replace the head light switch for sure. Also this switch, he looks new.

Strange, everything was working very well before.....

Daniel


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post #4 of 16 (permalink) Old Aug 7th, 18, 11:22 AM Thread Starter
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Ok, one step forward. I found the reason why the headlight front doors are not open anymore. The circuit braker is doing his job and brake the circuit. If I short cut the circuit braker, the dors are working well.
How does this circuit braker work? Is this a kind of fuse and is burned and need to be replace? Is it the same as at the firewall?
I hope someone can give me more information about this part.

Daniel


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post #5 of 16 (permalink) Old Aug 7th, 18, 11:54 AM Thread Starter
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..and the battery junction block behind the battery is also melting. Reason for this, the nut was loosy and the cable where loosy as well. Really bad conntact brought heat at the plastic part starts melting.
Could this be the main problem?


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post #6 of 16 (permalink) Old Aug 7th, 18, 01:03 PM Thread Starter
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Re: Burnt tachometer

..and the picture of the melded battery junction block.
Could this be the reason for all the electrical problem I have described above?

Daniel
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post #7 of 16 (permalink) Old Aug 7th, 18, 01:26 PM
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Re: Burnt tachometer

Cant say for sure but it is real possibility.
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post #8 of 16 (permalink) Old Aug 8th, 18, 05:48 AM
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Re: Burnt tachometer

I would start with that loose and melted junction point, then troubleshoot further, if needed. You just may have found the issue. However, the tachometer circuit board will need to be replaced or repaired. Not sure if you could simply identify the burnt resistor ohms value and solder in a replacement. I see in the picture there is a chip, a diode, and other circuit components that may have cooked due to that resistor getting hot. Without a schematic of that circuit board, its a guess.

As to your question on circuit breakers and relays, relays work as a high current switch, and a circuit breaker works as a high current fuse. Because the head light doors require more current to operate, a relay and circuit breaker are used to protect this electrical circuit. Typically, anything requiring 20 amps or more can use a relay and a breaker. A relay uses a low current "trigger" (the head light switch in this case) to open/close the relay. The relay will have a large gauge wire connected carrying voltage (current) to the 'input' of the relay, and the circuit breaker is protecting this. A smaller, lower current gauge wire (from the head light switch) will operate the contact in the relay, and allow the high current 'input' to be switched to the high current 'output' of the relay, to the headlight motor.

A switch, such as your headlight switch would not be able to carry the higher current load of the headlight door motors without burning up its contacts quickly, so relays and circuit breakers are used.

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post #9 of 16 (permalink) Old Aug 8th, 18, 08:18 AM
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Re: Burnt tachometer

The headlight door circuit breaker is designed to reset after being tripped. I replaced mine along with the relays for under $40 with parts recommended in the attached link. I had a hard time finding one to fit the stock bracket, but I made a larger CB work after modifying the bracket. Any two pole auto circuit breaker should work for you. If I read this quote from the link correctly, it looks like a 30 amp CB is required for a convertible.

Quote:
The RS circuit breaker is rated at 10 Amps. Do not replace it with the identical looking convertible circuit breaker rated at 30 Amps. To check the circuit breaker connect a test light from ground to the orange wire terminal, if the test light does not light the circuit breaker is bad. Note: years of use can weaken the circuit breaker and cause unintended tripping even if there is no short in the system. An identical replacement is hard to find, but similar post-style circuit breakers can be purchased at your local parts store for about $10.
https://retro-electro.net/FAQ67.html
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post #10 of 16 (permalink) Old Aug 8th, 18, 03:11 PM
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Re: Burnt tachometer

Quote:
Originally Posted by elan71 View Post
..and the battery junction block behind the battery is also melting. Reason for this, the nut was loosy and the cable where loosy as well. Really bad conntact brought heat at the plastic part starts melting.
Could this be the main problem?
That would explain the headlight switch killing the engine. Big current draw through a bad connection interrupting power to the ignition circuit. That connection feeds every circuit in the car except the starter motor.

The resistor fried because it was carrying more current than it the circuit was designed for. It's a big resistor - probably 3W or more, and drops a lot of voltage. Something downstream from the resistor shorted - if I had to guess, I'd say IC1 shorted. (2 or 3 diodes there as well that could have shorted) If it shorted it will probably remain unknown as to why - sometimes they just fail. It's possible it shorted due to the interrupted power supply due to the bad connection at the junction block. Be sure and check the condition of the pink wire that supplies 12V to the tach - it likely got very hot as well.


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post #11 of 16 (permalink) Old Aug 8th, 18, 10:14 PM Thread Starter
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Re: Burnt tachometer

Thank you for all your answers.
I have ordered all components now and wait until they arrive. Following the parts list, it is a 10A headlight door circuit breaker for the RS headlight. Unfortunately, I quickly found only a complete tachometer. The PCB board is too burnt to repair. It still smells very bad...Yes, I think it was a 3W resistor.
I'm pretty sure the bad conntact is the problem. If the voltage drops, the current increase and the resistor is getting hot.
All wires are still looking good, but I will double check all wires again.

Daniel


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post #12 of 16 (permalink) Old Aug 9th, 18, 09:38 AM
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Re: Burnt tachometer

The AIM only shows one part number, 4749164, for the circuit breaker (AIM pg. 427/UPC Z22-B7). An exact reproduction part is available if your concerned about originality or exact fit. I can't find any reference to a different part number for the headlight CB for convertible on any of the sites I searched.
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post #13 of 16 (permalink) Old Aug 9th, 18, 01:33 PM
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Re: Burnt tachometer

Kind of sounds like the alternator voltage regulator has failed causing the alternator to output a voltage higher than the normal 14.3V. This would explain why both the headlight door circuit breaker, tach resistor and the melted junction block connector.

Try measuring the battery voltage with the engine running. Also check that the alternator bulb still works as it may be burnt out now.

Last edited by blitzer454; Aug 9th, 18 at 01:45 PM.
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post #14 of 16 (permalink) Old Aug 9th, 18, 04:23 PM
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Re: Burnt tachometer

If the Voltage Regulator is at fault and it is a factory style mechanical you can adjust the output. It is a dying art these days but when I was a kid you had to adjust the VR all the time to compensate for age of lead-acid batteries and weather. Or the best solution these days is to replace the mechanical VR with a solid state such as a Wells/AirTex unit. I know the shipping to Switzerland might be four times the cost of the actual unit, but well worth the price if you are not able to local source one over there.


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post #15 of 16 (permalink) Old Aug 16th, 18, 12:23 PM Thread Starter
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Re: Burnt tachometer

Just closure:
The cause of all the problems was the loose contact on this battery junction block screw.
I replaced this one and make sure the contact is good. Replaced the circuit braker for the light doors and the tachometer as well. I also replaced the light switch just to be sure.
Now everything is working fine again.
Well, just a screw brings so much trouble. I will check this frequently from now.
Thank you all for your support and help. Great forum!!

Greetings from Switzerland
Daniel
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