electical demon

[69 red fastback 20]

I hope some of the electical experts here can help me with this problem, everything works as it sould I.e. gauges, lights, horns, except when I turn the headlights on it will actually kill the car, I've put on new alternator, voltage regulator. What am I missin, could it be a ground issue, a short somewhere? Any help would be greatly appreciated, Thanks

[SA69mach 39]

Not an expert, sorry. 

The headlight switch is an important electrical component, as it controls and feeds many other components.  They also can often be the cause of electrical failures, so I would suggest to remove the switch and check it thoroughly for connections and functions, or just try another unit.  Available from most any parts store.

If you are handy with a multimeter, and 12 volt power feed, and also have a test light, this diagram of the switch terminals may help you. 

​

 

With the headlamp switched to off, perhaps you can test for power at the IGN terminal, and then pull the headlamp switch to ON, and see if you have an interruption, or failure at the IGN terminal.

 

I would change out the switch and try that first, if it were me, then test the old switch for faults.  Best of luck.

[69 red fastback 20]

Thanks for the reply, I forgot to mention that I have already change the headlight switch also, but I will take it out and give it a good checking

[RPM 1,190]

I recently read of this same issue on another forum, maybe mustang steve or vmf, but I don't recall. May want to google with those names included.

[1969_Mach1 333]

That is an odd issue.  Are all the grounds in place.  Headlight grounds are good, there are good ground straps between the engine and body?  The headlight harnesses have plugs in front of the radiator, If you unplug the headlight harnesses so the lights are inop then turn the headlight switch on does the engine still shut off?

[danno 128]

You could have a hard short between the wires to your headlights and chassis ground.  That will kill the engine. But I have some questions to narrow this down.  When you turn on the light switch and the engine dies, do the headlights actually turn on? Can you turn on the headlights with the engine off?  What do they do then?  Pull up the carpet by the hi beam/lo beam switch on the floor and look at it. It is common for a short in either the wires to it.  For that matter, disconnect the  wires to it and see if it still happens?

[69 red fastback 20]

Thanks guys for the replies, I have

[69 red fastback 20]

Sorry for the last one, my fat thumb hit the send button, I haven't tried unplugging the headlight harness yet, that was my next thing to try,:I should add that it is an automatic and it's when I put it in gear is when it will die, I have checked my grounds and all seem to be good, and yes the headlight will still stay on when it dies, and they will come on with the engine not running. The funny thing is that when I turn just the parking light on everything is fine, it's just when I turn on the headlights. I will pull up the carpet and check the dimmer switch to see if it's the culprit. I would also like to add that when I did a voltage check at the battery and the coil, running I had 14.6 at the battery and 12.6 at the coil but when I turned on the headlights the battery was about the same but the coil was all over the place and I mean anywhere from 12.6 to 119.5 and yes you read those numbers right, thats the part that I don't understand

[1969_Mach1 333]

Aside from the headlight issue, if you are still using the stock points ignition system you shouldn't have 12.6V at the coil when it is running.  It should be closer to 6V because the power feed wire to the coil goes through a resistor wire to reduce the voltage at the coil when running.  Maybe a previous owner bypassed the resistor wire.  Some tough issues.  Check grounds and engine to body ground straps.  The headlight ground attaches to the rt. inner fender below the starter solenoid.

[69 red fastback 20]

Thanks for the response, I'll check my grounds again

[Raven R code 281]

Contact Midlife.

[69 red fastback 20]

Thanks Raven R code I'll send him a pm

[Midlife 814]

I read this early in the morning and really didn't want to reply without my 4 cups of coffee.  I PM'ed him with a couple of questions (halogens?) and provided a trouble-shooting tree by removing all bulbs on the headlight circuitry (headlamps, running lamps).  That should isolate where the problem is: most likely with a near short.  Otherwise, his voltages sound reasonable so long as the headlight switch is not on.

[69 red fastback 20]

Well thanks to Midlife we narrowed it down to the halogen lights, so now my guestion is, is it worth staying with halogen lights and putting a relay on them or just go back to the incondesent lights. If I go with a relay, can anybody recommend a good relay kit.

Thanks in advance

[69 red fastback 20]

Well I found out my problem was the pink resistor wire going from the ignition switch to the coil. So I did away with the pink wire and ran a 12 gauge wire from the ignition switch to the coil and all is good.

Thanks to everyone for all of the advice.

[RPM 1,190]

Good news! And thanks for posting the cure.

[danno 128]

You better be careful, because that pink wire is the resistance wire for a reason, you need a resistor wire there.  A 12 gauge wire has essentially no resistance.  You can blow up your coil if you hook the full voltage up to it all the time, and this will happen only when the lights are off.  For a short time you can do it, but it will die eventually.

 

So either

1. your resistance wire is bad, and needs to be replaced by another resistance wire

2. your voltage at the ignition switch is low with the lights on, and so by the time the current goes through the resistor wire, it is too low to run the car.

 

I would guess the problem is #2.  You are solving it in a different way by using the #12 wire in place of the resistor wire.  That is not the correct solution. This will blow the coil eventually when you drive with the lights off.  The problem is a combination of things, but the halogen lights are the biggest cause of the problem.  Get the relay kit for them and all will be better. Until you get the relay kit, if you leave the 12 gauge wire in, drive the car with the lights on all the time!  That way the voltage to the coil will be lower.

 

Let me explain it a bit differently.  There is resistance in all wires, some more than others. Resistance drops the voltage, and the amount of voltage it drops depends on how much current is in the wire. So the high current needed for halogen lights drops the voltage at the ignition switch to a lower voltage.  Then you also have a wire from the ignition switch to the coil, and it also has resistance. It is designed to have a high resistance for a wire, and will typically drop the voltage down about 3 volts. So with your lights off, you have 14 volts at the battery, 12 volts at the ignition swtich, and 9 volts at the coil.   You turn on the lights, and the voltage at the ignition switch drops to 10 volts, and the same 3 volt drop in the wire from the ignition switch to the coil means the coil only gets 7 volts.  7 volts is too low to run the car, but 9 volts is.  The voltage numbers I mention are what it could be, you could measure slighttly more or less.

[Rsmach1 71]

I've always ran 12v to the coil, and have never had an issue. The reason these cars had a resistor was because they ran points. With an electronic ignition and aftermarket performance coil it's preferable to run 12v.

[danno 128]

Rsmach, I know that running 12 v without a resistance wire can be done with solid state ignition and a good coil.  I was thinking 69 Red had standard points and coil.  Even with solid state ignition and with a standard coil, running full voltage to the coil will cause it to be a lot warmer than what it would be without the resistance wire. Running a coil hotter than it should be will shorten its life.  You are also right in that most ( or all?) aftermarket pecformance coils are designed to work on 12v, not the reduced voltage with a resistance wire.  So the critical question for 69 Red is what coil is in the car?  Standard factory coil or aftermarket performance coil. 

[69 red fastback 20]

danno,

 

Thanks for the explanation, that is how I came to the conclusion that the resistor wire was the problem. I am running the MSD 8352 ready to run distributor and the MSD 8202 Blaster 2 coil, I had the Mallory 29216 coil on it, and I think that is what I did was burn it up, after doing some research the Mallory coil likes the resistor wire, and I think that's why my car was running like crap, because sense I bypassed the resistor wire and put on the msd coil the car has never ran better.

 

Thanks for the responses

 

Joe

[danno 128]

OK, sounds good.  I am glad you got that figured out!