I would like to check the timing on my 91 F250 w/ 7.5L 460. I have timing light, and know how to unclamp and rotate distributor cap and know about timing marks (10BTDC). The sticker on the hood has some basic instructions, warm up engine, then unplug something, then check timing. I do not know whether it is an electrical or vacuum line I unplug. From past experience with other cars, this is some type of timing advance vacuum or electrical signal.

As I recall, I clamp the timing light onto #1 plug wire and battery +. Any help in what I need to disconnect would be welcome.

Thanks,

Regan

 

There is a spout connector (square plug) usually near the distributor in the wiring going to the TFI module on the dizzy. By unplugging this, the computer will not advance the timing and you will get an accurate base timing setting with a light.
Yes, the timing light clamps around the #1 plug wire, usually as clost to the plug as you can and then a + and - to the battery.

With the spout plug in, the timing will show way advanced with a light.