Mariner 75hp 4 Cyl Trim Gauge Problem

[Glastron1987]

Last spring I picked up boat with a (roughly) 1984 Mariner 75hp outboard. It is a 4 cylinder. Appears to be 2/3 of an inline 6. Anyway, it appears that a trim gauge had never been used on it as the trim sensor on the swivel bracket was missing. I installed one (the sensor) and a gauge. It does not work because the swivel bracket is not properly grounded. When I manually ground the swivel bracket, it works fine..so I did install everything properly. I see a grounding strap connected between the lower part of the swivel bracket and the bolt for the motor mount on the mid section which is grounded. The strap appears the be good and tests out fine. The problem is that the mounting bolt is connected to the mid section with rubber, so that is where the connection ends. Anyone know how the ground is supposed to be completed? I don't see any other grounding straps in that area that would complete the connection.

 

[achris]

Re: Mariner 75hp 4 Cyl Trim Gauge Problem

As you suspect, there should be continuity between all major parts of the engine... There should be a ground strap between the drive-shaft housing and the through bolt for the lower mounting...

Have a look for item 16 on this diagram...

http://www.mercruiserparts.com/Show...7&bnbr=180&bdesc=DRIVE+SHAFT+HOUSING+ASSEMBLY

 

[Glastron1987]

Re: Mariner 75hp 4 Cyl Trim Gauge Problem

The strap pictured there looks like the one I see connecting the swivel bracket with the end of the mount bolt just under the nut. That all seems good, but then the continuity ends at that bolt, as though the bolt does not actually contact the drive-shaft housing. I wonder if I'll have to pull that mount out to see what is going on in there.

 

[Glastron1987]

Re: Mariner 75hp 4 Cyl Trim Gauge Problem

In the picture, there is continuity going from the swivel bracket to where the grounding strap connects (my finger), through the strap, and through the mounting bolt. Continuity ends at the mounting bolt, because of the rubber surrounding it and does not travel into the drive shaft housing back to the engine. To me it appears that it is a mercury/mariner design flaw that only becomes apparent when someone tries to install a trim sensor and guage.