Accessory switch position

[lutronjim]

I had to install a new switch because my truck would sometimes not start. The old switch would not go to the accessory position.

I have a ls conversion and the old wire to the coil must go to the computer - a friend installed.

Now when I move switch to the accessory position, the check engine light light comes on waiting for the start cycle just like when its in the run position.

Originally would the accessory position let you play the radio without running current through the coil and points?

[dmjlambert]

Some of the circuits get voltage when in accessory position, and some circuits get voltage when in in run position. When in run position the accessory circuits also get voltage. So, yes, accessory position does not normally power the engine components such as the coil or electric choke. I don't know in what positions a computer or check engine lights are supposed to be powered, as my truck doesn't have that stuff. But I'm sure others will chime in on that subject.

['68OrangeSunshine]

'67s and '68s don't have them stock. The ''ACC'' position is a later design function.

[LH Lead-Foot]

The "LS" conversion that uses a CEL, is hot while in run position at ignition switch as the PCM provides ground to turn it on when needed. In the ACC position, you may have to change your current wiring at the ignition switch, which is not too hard.
The "Bulb Check" circuit is a connection between RUN and Crank on many ignition switches and shown on schematics. With the switch removed, use a volt-ohms meter to check the back terminals for each operation and the identification is stamped on the back. Many have a terminal for grounding thru the ignition switch case to run a Bulb check operation for brake pressure switch and coolant switch. This will not work for coolant senders as they change resistance rather than open or closed like the OEM switch for dash lamp.
Most likely, you will just have to remove one wire and reposition with run terminal. Depending on your dash, OEM type or aftermarket digital, there are not of bulbs to check with the ignition switch.