Switched Ignition Source

[Elliott Taylor]

you need an underhood or underdash source?

Either, actually. Just a clean source

 

[Elliott Taylor]

You have to remember that when they are designing things, not always are the systems going to be put on pristine cars but could be going on cars with fresh brand new harness with minimal voltage drops or they could be put onto cars that the wiring harness is so shot and poor that there is excessive voltage drops to things. Case in point look at guys adding headlight relays. A lot of times it does work on older cars but not in all cases and if there is a difference, it might be so small you never see it.

IF for some reason the IGN terminal is dropping too far down on voltage, then the relay could be the answer but to confirm this one would need to take measurements at the IGN terminal and then at the battery to see how much difference there is.

I also have to think these systems have a working voltage window in that they should work with voltages between let's say 10V and 15V. Going above or below this might not have the system working like it should.

Just keep in mind that the IGN terminal (as well as the ACC, BAT, and LPS terminals) in the fuse block are protected by a neighboring fuse and one could add too many things to the "tap" as I call it and if it does become overloaded one just cannot pop in a larger fuse as the supply side of things is only so big.

Jim

This might be stupid.. but when you say check the voltage do I check it with both wires in the IGN terminal, or without anything attached ? I assume having the wires attached will bring the voltage down ?

 

[Jim Streib]

This might be stupid.. but when you say check the voltage do I check it with both wires in the IGN terminal, or without anything attached ? I assume having the wires attached will bring the voltage down ?

There is no such things as a stupid question. You just need to wrap your head around what needs to be in a spot for voltage and whether or not the car in different spots can supply that.

Basically you want to check before adding things to the IGN terminal and take some readings with the key being turned to the RUN position and then another reading when they key is turned to the CRANK position and the motor is being turned over.

There should be a specification that what you are adding needs to see at LEAST a certain amount of voltage and cannot drop below a particular number for it to work as designed. In other words if you measure on the IGN terminal 12.1V with the key on and then it drops to 10.5V when cranking over the engine, then this is what it is on the output of the IGN terminal in the fuse block. If now they say you need at least 11.0V for the setup while cranking over then the IGN terminal has an output that it too low by 0.5V which means things will not work as designed. If this is the case then one needs to do some more measuring at the battery to see how things are and it's possible that the battery may show a slightly higher voltage drop when cranking over than at the fuse block but if it is too low there also, then a relay is not going to help things at all. In other words let's say you measure at the battery and it measures 12.3 instead of 12.1 like it did at the fuse block with the key in the run position this is good but now while cranking over the motor the voltage at the battery might dip down but not to the 10.5V like it did at the fuse block but would drop to 10.8V, then even with a relay the voltage is not high enough for the system that needs 11.0V to work as designed.

Now these are just some random numbers to throw out but you can try using the IGN terminal for your source and if it stays higher than what the system requires, then things should work. If things do not, one could just try running a temporary wire out to the battery to see if things then would work and if they would then a relay can be added.

Once you get everything running and working then also do yet another voltage check with the engine at idle and then at a highway RPM to make sure the voltage does not go above let's say 14.5V-15.0V because if it goes to maybe 18 or 20 volts then things could also turn off due to excessive voltage levels.

Jim

 

[BonzoHansen]

Either, actually. Just a clean source

The pink HEI lead under the hood is hot in run & start. You could use that to trigger all the relays you need

 

[Elliott Taylor]

There is no such things as a stupid question. You just need to wrap your head around what needs to be in a spot for voltage and whether or not the car in different spots can supply that.

Basically you want to check before adding things to the IGN terminal and take some readings with the key being turned to the RUN position and then another reading when they key is turned to the CRANK position and the motor is being turned over.

There should be a specification that what you are adding needs to see at LEAST a certain amount of voltage and cannot drop below a particular number for it to work as designed. In other words if you measure on the IGN terminal 12.1V with the key on and then it drops to 10.5V when cranking over the engine, then this is what it is on the output of the IGN terminal in the fuse block. If now they say you need at least 11.0V for the setup while cranking over then the IGN terminal has an output that it too low by 0.5V which means things will not work as designed. If this is the case then one needs to do some more measuring at the battery to see how things are and it's possible that the battery may show a slightly higher voltage drop when cranking over than at the fuse block but if it is too low there also, then a relay is not going to help things at all. In other words let's say you measure at the battery and it measures 12.3 instead of 12.1 like it did at the fuse block with the key in the run position this is good but now while cranking over the motor the voltage at the battery might dip down but not to the 10.5V like it did at the fuse block but would drop to 10.8V, then even with a relay the voltage is not high enough for the system that needs 11.0V to work as designed.

Now these are just some random numbers to throw out but you can try using the IGN terminal for your source and if it stays higher than what the system requires, then things should work. If things do not, one could just try running a temporary wire out to the battery to see if things then would work and if they would then a relay can be added.

Once you get everything running and working then also do yet another voltage check with the engine at idle and then at a highway RPM to make sure the voltage does not go above let's say 14.5V-15.0V because if it goes to maybe 18 or 20 volts then things could also turn off due to excessive voltage levels.

Jim

Hey Jim just thought I’d let you know your idea worked, and I got the car running yesterday. Short of a heater hose leaking, everything went well. I checked out several Holley videos over the past few days and they all agreed I’d have a small voltage drop in cranking(which I did to about10v). Thanks for all your help.

 

[Jim Streib]

Glad you got it going.

I know I've had my share of voltage issues through the years from installing car audio since the late 70's and all this stuff has an operating window. Go too low or too high and things don't work. You just want to make connections solidy and have reliability so that down the road you don't have issues.

Hopefully your heater hose leak is not from what a rodent can do when they chew through things (mine from last year).

Jim

 

[BonzoHansen]

i hope he drank the antifreeze

 

[Elliott Taylor]

Glad you got it going.

I know I've had my share of voltage issues through the years from installing car audio since the late 70's and all this stuff has an operating window. Go too low or too high and things don't work. You just want to make connections solidy and have reliability so that down the road you don't have issues.

Hopefully your heater hose leak is not from what a rodent can do when they chew through things (mine from last year).

Jim

Not quite that bad haha

 

[daustin]

Hello,
On a lot of these cars the ignition "on" dosen't supply power to the distributor while cranking. That was supplied from the second terminal on the starter solenoid. That jumper wire is commonly deleted, but is essential for distributor power while cranking. Usually a yellow wire. The reason is the distributor on points cars ran off either a ballast resistor or a resistance wire so the points would last longer, usually around 9v. The wire from the starter was 12v, higher voltage while starting.
Don

 

[BonzoHansen]

Hello,
On a lot of these cars the ignition "on" dosen't supply power to the distributor while cranking. That was supplied from the second terminal on the starter solenoid. That jumper wire is commonly deleted, but is essential for distributor power while cranking. Usually a yellow wire. The reason is the distributor on points cars ran off either a ballast resistor or a resistance wire so the points would last longer, usually around 9v. The wire from the starter was 12v, higher voltage while starting.
Don

HEI cars are different. No ballast either. Liks the OP's 77. I guess that change was mid-74 as HEI was introduced.