My bus has no outside door under the driver's window. On the inside is a panel with a dozen switches. Inside is 1 std 4 wire relay. I'm looking for the 5 wire crank relay. Down by the drivers left foot are 3 std relays. Outside on the firewall are 3 identical std relays for ECM, IDM, and XMSN AT.
The manual for "1997 3800" points to the interior right side firewall-dash area. No wiring or holes to mount relays. I've seen relays there on larger international trucks.
No build thread but pictures and text are at