1977 70Hp Johnson tach question

[Tacklewasher]

So, I picked up a new to me boat this week that came with a 1977 70hp Johnson. Model # 70EL77S.

The boat also has a rather old looking Airguide Tach.

Of course the Tach doesn't work. Mind you none of the gauges work for various reasons (no pickup for the speedo, no fuel tank for the fuel gauge). The tach basically pegs to full sweep when the motor is running.

Now, my plan is to make sure this motor runs well and then sell it. I have a 1981 Evinrude 115 that I want to replace it with. The boat is rated for 150 so I have no issues there.

I have a nice manual for my 115. I don't have a manual for the 70. I don't want to buy one for the 70 but I would like to get the tach working.

Is the wiring for a 1977 similar to a 1981? The controls are different, but mostly because the trim switch is not on the controls but is on the dash. I'm thinking they can't be that different. Once I toss a voltmeter on to be sure the motor is charging, can I troubleshoot the tach with my 115 manual?

Any help is appreciated. And no, I won't be buying a manual for it (sorry).

 

[wilde1j]

Re: 1977 70Hp Johnson tach question

If the tach has a pulse setting, it needs to be set for "6P" ... there's only two wires that count a black ground and a grey wire (int illumination will add an extra lead for the lamp.) If it's connected correctly and doesn't work, time to try Ebay, etc.

 

[jtexas]

Re: 1977 70Hp Johnson tach question

yes, the 1977 and 1981 tach wiring is the same. SND = gray, IGN = purple, GND = black

if the rectifier is original, it might have one yellow and one yellow/gray wire, instead of 2 yellows, doesn't make any difference though.

 

[Tacklewasher]

Re: 1977 70Hp Johnson tach question

Well.

I ran the motor on muffs with a voltmeter attached and running at a medium idle (gee, I wish I had a tach so I knew how fast it was idling) I saw no change in voltage.

I did not get the chance to check the rectifier but I'm assuming it's toast.

I'll test it tomorrow if I get the last bit of laminate installed. I really should do one project at a time.

 

[wilde1j]

Re: 1977 70Hp Johnson tach question

Other probable choice is stator. Measure across the yellows ... should get > 20 VAC. Note this is AC, not DC. Low or no voltage here means the stator needs to be replaced.

 

[jtexas]

Re: 1977 70Hp Johnson tach question

to test your rectifier:
http://forums.iboats.com/showthread.php?t=190638

 

[Tacklewasher]

Re: 1977 70Hp Johnson tach question

Yeah. I have that printed out.

Just ran out of daylight is all.

 

[Tacklewasher]

Re: 1977 70Hp Johnson tach question

Oh well.

The rectifier tests fine.

Time to look deeper.

 

[Tacklewasher]

Re: 1977 70Hp Johnson tach question

Well.

I let it run for a bit and it's charging fine. So I just need to track down the tach issue and the motor is not the problem.

Hmmm.

Time to pull the tach out of my other boat and see if it is the fix. Sure is nive having a spare parts boat of the same vintage/brand etc.

 

[Tacklewasher]

Re: 1977 70Hp Johnson tach question

Problem solved with the tach off my old boat.