Is this true or not?

-
cruiser

cruiser

Well-Known Member
Joined
Feb 26, 2016
Messages
832
Reaction score
925
Location
Bloomington, MN
Simple question: Does it harm your electrical system (1974 Duster, totally stock in my case) to leave the ignition switch in the "run" position for any length of time with the engine off? When I want to listen to the radio with the engine shut down, I move the ignition switch to the "accessory" position and everything works just fine. But my buddy says that to listen to the radio with the ignition switch in "run" with the engine off will damage the electrical system. The owner's manual doesn't address this issue. And why would it damage the electrical system with the engine not running, but not harm anything when the engine is running? Ideas, anyone? Thanks - cruiser
 
I have heard that it will damage the ECU. I'm not sure but think that is because it is designed to be constantly triggered and if the engine's not running, it is not triggered at all and something about it gets overcharged.
 
Do you leave your light switch on with no bulb in socket? Or off? That's essentially what leaving key in run position is doing. If radio listening is your fancy turn key 1 click back and listen away.
 
Old points distributors usually didn't like sitting energized without running. Using ACC was really important back then to not end up with points welded together

Ignition module being live and exciting the alternator are the two things that might be a draw. Doubt the ecu would be hurt by being live without a signal being sent.
 
Big.J.007 said:
Do you leave your light switch on with no bulb in socket? Or off? That's essentially what leaving key in run position is doing. If radio listening is your fancy turn key 1 click back and listen away.
Click to expand...
No bulb means no circuit. I don't think that you could say the same about a charged electrical system. If current is flowing (circuit), something is going to get hot I would think. I agree with @Uncle Bob on that one.
 
cruiser said:
Simple question: Does it harm your electrical system (1974 Duster, totally stock in my case) to leave the ignition switch in the "run" position for any length of time with the engine off? When I want to listen to the radio with the engine shut down, I move the ignition switch to the "accessory" position and everything works just fine. But my buddy says that to listen to the radio with the ignition switch in "run" with the engine off will damage the electrical system. The owner's manual doesn't address this issue. And why would it damage the electrical system with the engine not running, but not harm anything when the engine is running? Ideas, anyone? Thanks - cruiser
Click to expand...
That's why they have "Accessory". No need to power all the run circuits just because you want to listen to your radio.
 
The alt rotor is charged and creating huge draw and heat.
Without the alt fan turning, and the engine fan, - the alts gonna get hot, and drain the battery pretty quick, much faster than just the radio in acc..
 
crackedback said:
Old points distributors usually didn't like sitting energized without running. Using ACC was really important back then to not end up with points welded together

Ignition module being live and exciting the alternator are the two things that might be a draw. Doubt the ecu would be hurt by being live without a signal being sent.
Click to expand...

Exactly. To the OP Cruiser: Yes, the transistor and related stuff is energized in the run position. your friend is correct. Some good, old style 70-80's boxes may not care about being energized in the "On" position. The crap, fake transistor boxes surely will fail quicker. My stupid opinion.

I run points in my Jeepster Odd Fire 225. I left the key on one day last summer by accident, it welded the points. Fact.
 
cruiser said:
Simple question: Does it harm your electrical system (1974 Duster, totally stock in my case) to leave the ignition switch in the "run" position for any length of time with the engine off? When I want to listen to the radio with the engine shut down, I move the ignition switch to the "accessory" position and everything works just fine. But my buddy says that to listen to the radio with the ignition switch in "run" with the engine off will damage the electrical system. The owner's manual doesn't address this issue. And why would it damage the electrical system with the engine not running, but not harm anything when the engine is running? Ideas, anyone? Thanks - cruiser
Click to expand...

Just put your radio on a switch so you have power to it constantly.
That way when the switch is on you can listen with zero draw from anything else.
And when the switch is off it’s definitely off.

I put one right next to the lighter in the ashtray compartment.
It switches the stereo and the amplified antenna.
 
If you turn the key to ACC, no power to the ECU or field of the alternator.

With the key in run you have power to both.

No reason to put car in run unless the engine is running.

Will it cause a melt down, probably not, the OEM certainly designed the system to handle the oops when someone leaves the key in run for hours
 
It most certainly can burn a coil up with the key in run and engine off. I don't know what else it might do. Ballast resistor, maybe?
 
That is why there is an 'Accessory' position on the switch. So that accessories, cig lighter, radio etc can be used without the rest of the elec system being 'on'.
Only drawback is draining the battery if used for too long...
 
IDK guys The ECU system works just like points. Power goes to the Coil from the run circuit thru the ballast; but the other side is open circuit until the ECU closes it and without a signal from the trigger, the circuit stays open. Right?
but yeah IDK about the alternator. My guess would be that as the battery falls below a fixed threshold, the Regulator will close the field coil, and a modest current will flow. Without the cooling fan turning, she is likely to get warm.
I think it's a moot point tho, just use the ACC position and done.
 
It is like Russian roulette. We don't know where the points or reluctor stopped when the engine last ran, so it can cook the coil/closed circuit.
 
MV8 said:
We don't know where the points or reluctor stopped when the engine last ran, so it can cook the coil/closed circuit
Click to expand...
I may be wrong but the electronics are looking for a peak or a valley to trigger the coil to fire.

Does the coil charge when the engine is not running but the key is in the run position????
 
It depends on if the trigger threshold is on going high or going low. On an HEI, it is triggered ON/closed going high or around 1.6v depending on the module internals and OFF/open around 1.4v. If the value is between the two states, the module can end up in either state.
 
Last edited:
MV8 said:
It depends on if the trigger threshold is on going high or going low. On an HEI, it is triggered ON/closed going high or around 1.6v depending on the module internals and OFF/open around 1.4v. If the value is between the two states, the module can end up in either state
Click to expand...
That kind of makes my point

The reluctor is creating a voltage but only when it is rotating and if it is below a level it results in an open to the coil meaning no charging of the coil.
 
Note my last sentence. There is a current without the reluctor moving and the relative position of the reluctor affects the field. A bias voltage at low (and zero) rpm provided by an HEI to support low dwell time (around 1.3v). If it is above 1.4v and less than 1.6v (ambiguous) when powered up, it can be in either state until it actually crosses a threshold.
 
You must log in or register to reply here.
-

Back
Top