Before Posting, Please Read Our Posting Guidelines Below.
1. Use the full 4 digit year for everything you are asking your question about. Example: 1962, 1988, 2000, 2011 2. Include the correct name of your Whaler model. Example: Montauk 17, Montauk 170, Outrage 26, Outrage 260 3. Include the length when necessary. Example: 16, 17, 18, 20, 22 4. Do not post your email address anywhere on this site as it is already in your user profile.
Have a 1988 175 Mariner on a 21' Revenge. Engine runs well but tach is only accurate @ speeds below ~ 3000 rpm (separate tach verified). After that it either shows 0 or a silly high number in cruise (8500). Tach is properly set-up for engine and have changed tachs w/ same result. Also noticed today that several times in cruise, the charging system dropped out after hitting the trim button (voltage dropped to 12.4) and would not start charging again until engine was dropped to idle. At idle, voltage came up as expected (~ 13+V) and in cruise returned to ~14.7V. Hit trim, voltage drops to ~12.4V and stays. Drop to idle and systems starts charging again.
Dash voltmeter and voltmeter on GPS display agree.
Wiring from battery forward is new and solid. All new gauges w/ everything properly secured and terminated.
Have gone thru the engine wiring harness looking for shorts, cleaning and tightening all terminals, etc but no smoking guns. Starting to think the rectifier itself might be the issue.
Next step before just changing out the rectifier is to run a temporary wire directly from the rectifier to the tach bypassing the engine harness and see what the tach says then. But that still doesn't explain the charging system dropping out after a heavy load (trim motor).
I have essentially the same engine on one of mine (1988 Merc 150) and your problem is definitely either the voltage regulator, rectifier or stator, or possibly all three.
Update: Spent some quality time w/ the Whale today w/ a VOM after a good friend said the voltage issues sounded like a bad ground between the regulator and the block.
Hmmm. VOM didn't find any obvious problems but out of desperation added an additional ground wire from the voltage regulator body to a main ground on the block.
Lit up the engine on the hose/muffs and tach started working properly and the charging system came on line as expected. Trimming dropped the system voltage a bit but came right back up.
I think it's fixed. Will splash the boat tomorrow to confirm. Life is good.
