Need Tach clarification for 73 Merc 850

[rickdb1boat]

Re: Need Tach clarification for 73 Merc 850

Tach Hook up

 

[Jumper]

Re: Need Tach clarification for 73 Merc 850

It's got back lighting but it's on it's own wiring. I haven't been able to put the water on the boat yet to find out what the WOT rpm's are either. I'm hoping to do that Friday after work. But I don't remember the needle moving at all when I turned the key. Just stuck on 200. I know idle rpm's are around 1100 and the manual says the rpm's in gear while idling are around 500-600. I may put the motor in gear tonight and see what it reads. Or I may just forget all this headache and buy a new one!!

 

[Jumper]

Re: Need Tach clarification for 73 Merc 850

Ok. why did that post twice?

 

[Jumper]

Re: Need Tach clarification for 73 Merc 850

Thanks Rick. I actually had downloaded it the other day and was using it as reference. But Thanks for the effort!!!!! Glad to see someone is taking the time to help a boat rookie!

 

[rickdb1boat]

Re: Need Tach clarification for 73 Merc 850

Let me know on your progress! I'm getting curious as to what's going on with it. Hope it works out. 1000 RPM'S in neutral would be close and 700 in gear would be good! Let me know how it goes! Good Luck,

 

[Jumper]

Re: Need Tach clarification for 73 Merc 850

Rick<br />Not much progress to report as of yet. I did however, take the tach apart and basically "moved" the needle to where it sits back on zero again. Probably not the right way or smartest way to do it, but.... I'm going to hook it up tonight and see what rpm's I get now. I talked to a mechanic yesterday while picking up a new bilge pump and he said in neutral it should idle around 800-900rpms. I may get one of those "tiny tachs", hook it up to the motor on it's own and compare the two tachs to see which is right. Ever use one of the tiny tachs?

 

[rickdb1boat]

Re: Need Tach clarification for 73 Merc 850

No, I have not used them, but have heard good things about them! I think you are on the right track by checking with a different Tach. Let me know how it goes! Good Luck,

 

[mellowyellow]

Re: Need Tach clarification for 73 Merc 850

if your merc has the "thunderbolt" ignition it<br />requires a special tach. I would call teleflex<br />and ask them if your's is compatible. <br />perhaps you just have the wrong tach?<br />mine plugs directly into the front of the<br />control box and runs from there to rectifier.<br />looked in my seloc manual, but it doesn't tell<br />me what wires are what.<br />good luck,<br />M.Y.

 

[Jumper]

Re: Need Tach clarification for 73 Merc 850

It has the thunderbolt ignition, however, the tach was hardwired into the boat. I'm not even sure if the thing registers correctly which is why I'm gonna have it checked against another tach. If mine is bad, then I'm going to look for a tach with the MercControl plug to make it a little easier. So we'll see what happens! I'm hoping to have it checked out next week or maybe even tomorrow. We'll see. The boat shop closes at five, and I have a tournament on Saturday.

 

[mellowyellow]

Re: Need Tach clarification for 73 Merc 850

just trying to cover all the bases for you.<br />the tinytach is a good idea. <br />just 2 wires, plug wire and eng. ground and it<br />also measures engine hrs.

 

[Jumper]

Re: Need Tach clarification for 73 Merc 850

I definitely appreciate the info mellow! I wish it had the plug on the end of the tach but it only has two wires. I'm going to buy all new gauges this fall and the tach will definitely have the plug (I hope )