The Ford relay will not allow you have the Mopar Neutral Safety switch system in circuit and operating properly.
If you don't want to use a meter then use a 12v test light and do this sequence of tests:
1) Put it between the brown wire from the start relay and ground and turn the key to START. If you get a light, then the starter is the problem. Otherwise:
2) If no light above, then ground the G terminal of the starter relay and try again. (This simulates the neutral safety switch being closed to ground as it should to allow starting.) If it starts, then the NSS (neutral safety switch or its wire is the problem. If still no start:
3) Connect the test light between ground and the I terminal of the start relay (the yellow wire). Turn the key to START and see if the light lights, If yes, then the problem is the starter relay itself. If no light, then the problem is in the ignition switch or the yellow wire.
If you have around a 74 or 75 they had a seat belt interlock that will open the yellow wire circuit and prevent starting. So let us know what year car you have.