[masterhussey]

Car: 1974 Trans Am SD-455
Is there a way to test an ignition switch correctly (the one on the column, not the key tumbler)? Is there a specific process. I have been in the search of why my tach is acting strange. I have done the most common things you can think of and the car runs amazing. So far the only thing I have not checked is the switch. How much voltage is supposed to come from the switch to the coil? Is it a steady voltage? I don't want to replace the switch if I can figure out its something else.

[Bill Hanlon]

Points or electronic ignition?

[masterhussey]

here is what I posted to facebook.

Car: 1974 Trans Am SD-455
Update: So if you have been following a long with me. I'm trying to get my tach more under control. I have done the most common things you can possibly think of (if not please let me know if i missed something). the Tach is better but still not correct. I know there are some tricks with adding a resistor to the wire but i'm trying to figure it out before i get into hacks.
Grounds ✅
Points ✅
condensor ✅
radio supressor ✅
wire from distributor to coil ✅
coil ✅
Hooked up a separate tach ✅
checked cap and rotor ✅
check plug wires ✅
Things i'm unsure of....
what voltage should be coming from the ignition switch to the coil?
is that voltage a steady voltage or does it fluctuate?
How can I test the actual Ignition switch (not the key switch)
do i test it via voltage or ohms if ohms what are the correct ohms needed.
Is there a ground I missed somewhere?
You all have been so helpful.

[Bill Hanlon]

Originally Posted by masterhussey

Things i'm unsure of....
what voltage should be coming from the ignition switch to the coil?
is that voltage a steady voltage or does it fluctuate?

Given a points ignition the voltage on the coil + should be battery voltage when the points are open and around 9 volts when the points are closed.
The coil - should be battery voltage when the points are open and 0 volts when the points are closed.

[masterhussey]

what should the voltage be coming from the ignition switch to the coil?

[Bill Hanlon]

Depends on which end of the wire (coil or ignition switch) and if coil end, whether the points are open or closed.

At the ignition switch the voltage should be the same as read from battery + to ground. Refer to post #4 for at the coil + end.

[masterhussey]

awesome, thank you. do you know of any ways to test an actual ignition switch? I've only seen one video on youtube.

[Bill Hanlon]

If the voltages are as described in post # 4 and the engine starts of (ie. the bypass function of the starter solenoid is providing battery voltage to the coil + terminal when the starter is cranking) then the ignition switch is doing its job as far as the ignition system is concerned.

No guarantees as far as the ignition switch and the accessory system is concerned.