how to set timing on a 90 cadillac seville?

Answer 1

If I remember right you have a brown wire behind the plastic cover along the firewall,disconnect it and set the base timing to factory spec on sticker.reconnect and the computer takes over. If that's wrong you may have to disconnect the flat wide connector coming out of the distributor to do the same as above.

Answer 2

This model Cadillac requires that you jump the ALDL connector under the dash at terminals "A" & "B", adjust the base timing to 10° BTDC, secure the distrubutor and then remove the jumper lead.
The connector is located under the center of the dashboard, at the transmission hump, below the HVAC controls, to the right of the ashtray. It is hidden behind a plastic door "flap" and is defficult to see clearly.
It is easier to buy a "code Key" from a discount auto parts store and use that, because the tool is rigid and is properly spaced.

Good Luck and Merry Christmas