New Bosch "Red" Coil is Burning me Up

[Atazman]

I installed the "123 Electronic Distributor" a number of years ago and continued using my old "black" coil which measured 2 ohms.  The old resistor was removed from the circuit.  The car ran great.  Well..... I had $50 to burn so I just bought/installed a Bosch "Red" Coil.

It started right up but soon shut down and I had smoking wires.  It melted the insulation around the +12V ignition wire connected to the + side of the coil.  Turned the key back to "On", and the wire got hot again.

I removed the capacitor (maybe called a condenser) that is mounted on the coil bracket and is also normally connected to the + terminal on the coil.  All is good without the capacitor.  Took care of my fried wire and the car runs good again.

What happened to me today?  Why would this happen with the "Red" coil when the capacitor was connected on the "Black" coil for several years?

All thoughts are appreciated.

[teahead]

So what all wires are going to the + side of the coil?

what all wires are going to the - side of the coil?

Your old points condensor was still hooked up all this time before putting on the red coil?  Very odd.

[Atazman]

I will answer your questions, Teahead. 

Three wires went to the + terminal on the coil:  (1) red lead from the 123 unit; (2) +12V wire from ignition switch; and (3) the wire out of the capacitor.

Only one wire connected to the - coil terminal:  (1) black lead from the 123 unit.

I might have confused you, Teahead.  My123 ignition system has been in use several years and it has worked perfectly.  I just decided to install the new "Red" coil and hook it up exactly as described above.  I always thought the capacitor was for noise suppression on the radio. 

In thinking about all of this, I am wondering whether the capacitor just disguised the real problem.  My new theory is that I somehow grounded the +12V ignition wire when I connected it to the + coil terminal.  Either that or the wire had a fray in it and grounded out against the body of the car.  I think grounding it out is the only way for it to have gotten so hot that it melted the insulation.  I will test this theory tomorrow.

But........... do these coils really run hot?  After driving the car today (after fixing the wire and removing the capacitor) the coil was so hot I could not hold my hand on it.  Just wondering?

Fixing the wire from grounding out is what I believe solved the problem; I first thought eliminating the capacitor is what solved the problem.  I will check this theory out tomorrow by hooking up the capacitor again and watching it very closely.

[mdsalemi]

The function of a condenser (capacitor) in a coil ignition circuit is to reduce the spark at the contact points as they open in the distributor and thus minimise burning and pitting of the points. If you don't have breaker points (such as with a Pertronix, which is what I have) there generally is no need for a condenser in the circuit.

I still have the condenser, but it's only mounted for show. The resistor in the circuit isn't used either; I use it only as a "tie point"; several wires that need to be connected all meet on one end. I don't have the other end connected to anything.

From the 123 information I've seen, they recommend the Bosch Red coil, but there is no condenser shown in their wiring diagram.

For the Pertronix I have, I took their advice and got the Flamethrower coil. Never had an issue. I have not taken a temperature reading of the coil however.

[teahead]

I'll have to check next time my car is driven to see if the red coil gets hot.  I would think some, but not scorching.

Hmm...

[Tyler S]

The capacitor mounted on the side of the coil bracket and hooked to coil + is a radio interference capacitor installed on cars that had such code listed on the data card. When they fail they short to ground. It was probably already on its way out and the extra load switching of the 123 and red coil did it in. You can leave it removed as it serves no purpose with the 123 transistor circuit.
Also be sure your new coil has at least 1 ohms resistance and is a 12 volt internally ballasted coil. IMHO the red coil is a current hog and overkill for our engines.

[Atazman]

Thank you, guys, for your comments and thoughts.  I did some more testing today..................

My capacitor mounted to the bracket on the new "Red" coil reads "infinity" when checking ohms from the wire to the mounting bracket (the ground).  I conclude it is not shorted out.

My new "Red" coil measures right at 2 ohms from the - to the + terminal.  Conclude this is normal.

Reconnected the capacitor wire to the + coil terminal and everything appears normal with the ignition "on", and sending + 12 V to the + coil terminal.

My initial problem of melting the insulation on the +12 V ignition wire:  I'm concluding I shorted the +12V ignition wire when I first hooked up the new "Red" coil.  Repairing this wire appears to have solved my problem.

Still curious though.............. does your "Red" coil get hot enough to where you can't keep your hand on it?  Still concerned about this.

Thanks!!

[Nicolas Aristodemou]

I bought a coil with my 123 distributor from the 123 manufacturer..... no issues of overheating.... warm I would say but normal in an engine bay.....no suppression capacitors necessary...... Don't know the supplier of coils to 123..... could be Bosch, although they sell it for 2x the price of a Bosch high performance coil....

[teahead]

Just checked...my red coil maintained same temperature.  Barely got warm if at all.


Be sure you have no ground wires attached to the coil and/or distributor

[Atazman]

Thank you, gents, for your comments.  I will check my coil temperature again (away on vacation for 2 weeks). 

Come to think of it...... my coil was "hot" right after I cooked the insulation of the wires.  I would have to say it was shorted at this time, which could explain the temperature.

Appreciate your comments.

[Atazman]

Back from vacation and gave my 250 SL a good spin.  After several miles, I checked the temperature of my "Red"  coil and  I can barely hold my hand on it.  I would guess it at about 120-130 Deg. F.  Car runs good, but would invite others to "feel" their coil and get back to me with how hot it is running.

I'm still concerned something isn't right because of teahead's report that his "red" coil is running much cooler.

[mdsalemi]

OK, in order to do this diagnosis properly you’ll need to get away from subjective comments about temperature. Go to Walmart and buy yourself their non-contact infrared thermometer:

https://www.walmart.com/ip/Temperature-Gun-Non-contact-Digital-Laser-Technology-IR-Infrared-Thermometer

Of course there are a number of places where you can get similar items at all price points. Armed with that important tool, you’ll be able to make objective, not subjective judgments about temperature.

When you say your coil is hot, take a reading.

Now, since you are in an area where there are a number of 113 owners, arrange a visit. You can then compare various operating temperatures of coils. Also—perhaps most important, you can compare connections and the primary ignition wiring, seeing where various resistors and capacitors are located in the systems, and see how yours compares.

Don’t rule out getting another coil and doing a swap. I think I have two older coils in my kit-bag from before I went to the FlameThrower II coil recommended by Petronix.

[Atazman]

Thanks for all the good advice, Michael, but help me out some more.  What temperature range should the coil fall within?  Even having an exact temperature I have no idea if it is hot or cold, OK or not OK.  See what I mean?  If I do as you recommend (using a temperature gun) and get the temperature, can you tell me if the coil is OK at that temperature.  That's all I want to know.

Maybe I'm wrong, but I would expect my new "Red" coil to run hotter than my old "Black" coil.

[mdsalemi]

Thanks for all the good advice, Michael, but help me out some more. 

My Pagoda is in the museum but in the next few weeks before the snow files I'll be moving into my friend's service facility. I have an infrared non-contact thermometer and will tell you precisely what my coil temperature is.

I suspect all will be a bit different however--which is why I suggested meeting with other Pagoda owners. Also, I think you said you have the 123? Best to check their tech support and ensure you have all the right parts and all is wired correctly. Heat is never good for anything electronic...

From what I read the coils on any car should not be that hot to touch that they would burn you. Thus, they would have to be under 120F.

[Atazman]

OK.... back again with some actual temperatures of my new "Red" Bosch coil installed with a 123 ignition.  I conclude I do not have a "hot coil problem".

I used my Fluke IR temperature gun:

Coil temperature before starting the car:  65 Deg. F.
Coil temperature after a 45 minute drive:  113 Deg. F.
Fender temperature beside coil (after the 45 minute drive):  107 Deg. F.

If nothing else, this note might be used to compare your findings if you should be concerned.