Im not sure it’s a surge…. I suspect a drop. I’m not sure this is an obvious issue cause I’ve not seen any posts with an issue even like this.

 

This is what I suspected as well. I do have a 69 diagram, and I got my crayons out highlighting the paths of direct battery/alternator power, power out of the ignition switch, and where the power to the headlight / high beam switches come from and where they go.

Based on what I see, yes the power going to the lights and the ignition switch seem to be on the same circuit …. So I’m suspecting a voltage drop in that circuit when I turn the lights/highbeams on, and the drop is effecting the power in the ignition circuit, hence the ignition trigger going to the MSD box…. I think we’re Getting somewhere!

 

Yeah it seems like a quick loss of 12V to me. Get a clean 12V to the ign. wire on the MSD box and that will tell you for sure. And its an easy test with just a jumper wire.
I also agree with 4Vettes that you should wire in some headlight relays, but I would like to pinpoint your actual problem first.

 

Id also clean the main ground cable connections to the frame and battery.. I'm thinking if this is weak it could cause issues but I would also think you would have starting issues from time to time if this was an issue also.

 

I think the main ground cable and ground to battery is fine. I recently connected connected the MSD box to the main ground cable to the frame and disconnect and reconnected the battery ground (cause I disconnected it when I replaced the alternator). Both are tight and clean.
However, I am going to check the ground for the headlights itself in front of the car… I haven’t looked at the in probably forever.

 

Checked all grounds:

They are fine.

Connected the MSD Box’s ignition power wire to the horn relay:

The bucking issue did NOT occur when turning the lights or high beams on.


So…. I went ahead and put relays for the headlights and high beams…..
Problem NOT solved…. There is still a buck when turning the headlights and high beams on….

BUT…. The problem is definitely isolated….. there is definitely a split second voltage drop in the ignition circuit when turning the headlights and high beams on.

So the question now is…. What could be causing it? And how do I fix it?

 

Are you using stock sealed beams?

 

Yes

 

....


I think I know why now.....wire your MSD directly to the Battery, and the trigger wire to the fuse box IGN spade. Whatever it is connected to on the ignition switch may be getting interrupted by the light switch. THe power for most of the cabin electrics come into the headlight switch and then are routed out to the fuse panel and the ignition switch, just like the horn relay is a buss bar. ....I dont know what year they changed this but it does it in a 68 and obviously a 69. The ignition switch is just that, a switch and the power coming in is just rerouted from other sources, which is probably from the headlight switch.

Like yuou said that old analog system probably wasnt as sensitive to that quick trip

My MSD Digital 6AL is wired to the battry for clean power and I have a second small fuse box directly powered by the battery but has a relay that is trigggerd by the IGN spade.

 

The MSD is already powered directly from the battery…. I have a direct dedicated line from the starter.

As for the ignition power… the power for this comes from the horn relay, that line splits, one goes to light switch and the other to the ignition switch.

There is no voltage drop at the horn relay, based on my test of connecting the MSD trigger directly to the horn relay.

And now my lights are powered directly by using relays, so now that power isn’t coming from a switch that is powered in the split to the ignition.

So the ignition switch still has a voltage drop somehow. I’m not understanding how this can be.

 

one you are coming off a common lug on the starter, not the battery...even though you are connected to the battery you are sharing that power with other circuits so it is a dirty power.
two, the ignition switch doesnt get power from the fuse panel, it gets it from the light switch depending on what you are tapped into. the IGN spade comes from the ignition switch but I dont know from where, it may be a cleaner source.

you need to rewire your MSD box power sources

 

The problem is not the power to the MSD box. I’ve tested and established this.

The problem is isolated to the power going to and/or coming out of the ignition switch, which is what the MSD trigger wire is wired into. I was able to isolate this by connecting the MSD trigger wire to the horn relay, in which case the bucking issue when turning on the lights does not occur.

So, what I’ve done so far is remove the headlight’s power draw from the headlight switch…. Which is where the ignition switch gets power. I did this by adding relays to the headlights…. The headlight switch is now only activating the relays. The headlights get power from the horn relay. And because when the trigger is connected to the horn relay the buck is gone, we know the power at the horn relay is ok.

But even after all this, when I connect the trigger back to to ignition, the problem remains.

So where I’m stumped is why there is still an apparent voltage drop in the ignition circuit?

 

Obviously you cant read...good luck, I'm done here.

 

Ok relax there squid, I can read just fine. But maybe I’m not understanding you, or you’re not understanding me.

So help me out and explain why you think there is a momentary voltage drop in the ignition circuit… where the MSD trigger wire is connected to, when I turn on headlights.

Please assume the following:

1. The MSD main power is fine connected to the starter, dirty power or not, this circuit is fine. There is not a voltage drop here. I’ve tested to ensure the issue is not here. Take this out of the equation.

2. The issue does NOT occur if I take the MSD trigger power away from the ignition circuit. When connecting the trigger wire to another 12v source that is NOT on the ignition circuit, the issue is gone. Meaning I’ve isolated the issue to what comes out of the ignition circuit.

3. The ignition circuit’s voltage drop only occurs when turning the headlight or high beams on. And I understand that both the headlights and ignition share a common post for its power supply.

4. To take the load of the headlights off of the circuit supplying both the headlight switch and ignition, I installed relays. The headlight switch now controls those relays, which takes minimum power. The headlights themselves, get power directly from the horn relay. Which as mentioned earlier, does not have the voltage drop, because if I connect the MSD trigger wire there, there is no problem.

So, the problem is still in the ignition circuit. Even with the headlights no longer connected to the headlight switch, the ignition circuit momentarily has a voltage drop.

I don’t understand why this is, since the power to the headlights is not coming from the switch anymore, which is what shares the supply to the ignition switch.

Could the small amount of power to control the relays cause it?

Could the trigger wire be picking up…. Idk some kind of interference because it sits along the headlight wires? (note it does not sit along the headlight wires when I connected it to other 12v sources)… hmmm… I’ll test this. So in this scenario it’s not the ignition circuit at all…. Just the path that particular wire takes.

I wonder if this happens when turning on other high demand components on the ignition circuit…. Like the blower fan, etc… another thing to test…. Which may help confirm the interference theory.

Appreciate your thoughts with the additional context.

 

What I am trying to get you to understand is that regardless of what your headlights are doing with a power drop it isnt part of your problem in reality. You are being distracted by the headlights. You keep saying you are taking power from the ignition switch which may be getting power through the wiring associated with the headlight switch. The switch is mechanical and the voltage drop, interruption or whatever you want to call it is probably from the mechanical action of the headlight high beam switch or may be a ground issue somewhere in the circuit.....and again isnt your real problem. Your problem is you need a clean source of power for your MSD. YOur are taking it off the back of the ignition switch which you shouldnt.

First Ignore the headlights, find a better source of power for your trigger. Ive been trying to explain that you should look at the IGN spade on your fuse block and get away from your ignition switch. Do you know what exactly you are pulling the trigger power from on the back of the ignition switch....you said the previous owner wired it up, correct? Why are you trusting them? This is the easiest thing to do first and saves you a ton of troubleshooting and wiring nightmares

Take a meter to that spade and see if it is effected by the headlight switch, it should not. IF it does then all bets are off but we may be able to work around it. Take a relay and use the power from the IGN to trip the relay. Supply the relay directly from the battery, power the trigger from this relay and see if the headlight issue translates to the relay. If it doesnt then heres your clean power and you dont have to worry about the headlight switch.


If the work around doesnt work
.......disconnect the relays from your headlight switch so nothing is connected and then operate the switch so that moving the switch doesnt transfer any power. If it still effects your ignition system then good,,,disconnect the highbeam switch and try again. Then unplug the headlight switch and see if you loose power to the ignition switch or at least the wires you are taking trigger power from. you may have a bad switch, headlight or high beam or bad wiring. Atleast you will know that your power is not running its intended path. At this point I would make sure all the grounds are all good as well.

Bad news is if you cant find it this way you may have a short to deal with and you will have to disconnect everything and start tracing wires to see if there is cross talk somewhere. At this point you would have to disconnect all the wires and start ohming them out to each other...


when you say you have a voltage drop, how much of a drop do you see on your gauge and how long does it last. Do you have your dash off or are you doing all this from underneath?

 

What wire is this in the quote that is in red...IVe been believing you tapped into the ignition switch...is this a coil wire that went to your coil and is/ was cloth covered? Got a pic of it?

 

yes the wire is/was cloth covered. It gets 12v when the ignition switch is on.

and no …. when I say that I’m on the ignition switch I’m just referring to anything that is on the circuit after the ignition switch…. Basically there is power when the ignition switch is closed, and no power when the switch is open…. I should have been more clear there. I’m sorry.

In case it makes a difference…. Please Note that this car was originally equipped with the transistor ignition system….

 

I am with you now. Just one dumb question.
does the ignition spade on the fuse box have power all of the time? Or just when the ignition switch is on?

if the latter, that means it get its power after the switch…. Couldn’t the interruption in that circuit still also affect the tripping of the relay you’re suggesting I put on there?

 

So the original cloth wire according to the wiring diagram for TI would have come from the pulse amplifier and shows a resistor. How has this wire been modified to eliminate the resistor and the pulse amplifier? Diagram in link below.
TI Diagram.

 

Yes the spade is tied into the ignition switch but may be clean power. BUT

Now that I know you are tied into the old cloth covered wire those had a voltage drop when the car was started...Dont know how the light switch being an issue there but it is explicitly stated not to use those wires on an HEI distributor. The back of the ignition switch has a lot of different sources so that is why I was saying that it could be coming through the light switch. The IGN post should be a clean source from the battery or the horn relay. I havent traced it. I take it you are running your MSD under the hood in the engine compartment so try this...

This may be a solution for you. Use the Ignition wire you are currently using trigger a relay and take a direct power line off the horn relay buss bar as power for the MSD trigger through that relay. Y0u already know that is not an issue and the ignition wire voltage at the trigger side of the relay may be sufficient to keep the relay closed while you are running.
this will keep you from having to run a wire through the firewall