Re: how to install a trim and tilt on my1979- 70hp johnson which doesnt have one
I added the same unit to my 1978 70hp Johnson. Good score on the T&T unit. To mount it you do not need to take your motor off. Tilt the motor up and engage the traveling support arm. Suggest you place a 2 x 4 to hold the motor up in addition for safety. Now remove the left (port) mounting bracket and you will be able to install the T&T unit in place of the tilt assist unit. While you have the bracket off, suggest you go ahead and drill and tap the 2 bosses on the inside of bracket for 1/4-20 or 32 screws to mount the T&T sensor should you decide to add that. The bosses have a dimple marking the location for the screws.
Your still going to need a T&T relay box, cable (can make yourself), connectors, and T&T switch. If you have the older controller, TH Marine makes a nice T&T switch that goes in place of the plastic cap on the throttle lever. Used that on my first boat. Didn't say whether T&T motor is a 2 or 3 wire version. This will affect which relay box you need I believe.
Here to help should you need further.
-- Jeff