distributor replacement

[oltronj]

I need to replace the distributor on my 91 crew cab with a 454. ,I am told there is a wire I need to disconnect and then set the timing with a timing light and then reconnect the wire. I have never done this on a computer controlled engine so I am just looking for a little guidance. This truck is the old square body style and I also need to know where this wire is at. Any help is greatly appreciated.
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[ChevyTech]

To set the timing you must unplug the set timing connector.

On a square body, the connector is by the brake booster.

Look for a single Tan wire with a black stripe/tracer on it. On some square body trucks (I think 1987) the set timing wire is tan with a white stripe/tracer. Doing this will cause the check engine light to come on and will set a trouble code 42 in the computer. Clear the code after you are done checking or setting the timing.

[oltronj]

Ok I will look for the tan wire. Thank you. I should be able to reset the code just by disconnecting the battery correct? Also is it correct to set the timing at zero with the light? Or is it better to advance it a little bit?
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[ChevyTech]

Disconnecting the battery will clear the code. Make sure the key is OFF when disconnecting and re-connecting the battery.

I think the big block (454) timing specification is 4 Degrees before TDC.
Small blocks are zero degrees.
It should show the spec on the emissions label under the hood, if it is still there.