Need some mechanical advise, tach on 92 astro scx18 w/merc135 acting up. Acts like it is getting a signal part time only at higher rpm. Checked all fuses and connection that are known to me, need some advice on exactly were the signal is generated from for the tach. Also the temp water temp gauge has died with tach.

The tach signal comes from the Rectifier or voltage regulator..The temp sensor is in a cyl. head. Since you have problems with both I'd guess that it is a main harness issue or it's a faulty ground or power wire to gauges.. Does it have a panel (flush) mount control box or side mount control box?

If it's a side mount it has a harness that plugs into the control box and connects to the tach etc

Thanks, it has a side mount control... will check out tomorrow during daylight.

There is a test you can do, when the eng, running,take a volt teast on the craken batt, it schould be reading 13 volts or higher. I have a 200 hp merc and I had to disconnect the volt reg, it would short and take out the rectifer. IF you have ever shorted you power feed to the batt. it will take out the fectifier.  I would get a service manual,it will have all the steps you need to take to find the problem.

;)My dad had the same problem with his boat. I think he said the Marina replaced the wire coming from the voltage regulator. I'm not sure though I'll ask him about it and get back with ya.

Tight Lines,

Fatdaddy151

I did the test on the regulator from my seloc manual today and the it failed one of the ohms test, will replace this weekend and see if that clears it up. This has to be it, no other explaination.

Not sure how you made out on this but I just joined the group and went through the same thing this spring. The answer was a control module that I believe is located under the fly wheel. It is a little deck of cards sized hunk of epoxy sealed electronics and when it starts to fail strange electronic things start to happen. Such as the Tach giving you some very odd readings or no reading at all. I think it ran about 150-160 to get changed but it made a large difference.

Problem was fixed with a new voltage regulator, easy 35$ fix and runs fine.

Congratulations!!  I wish every boat/motor repair was $35 or less.  I'm not that lucky.

Your lucky, most boats I've owned or have been on do not have working Tach's.