1977 70 hp Evinrude 70773S

[fabieber]

Can a tachometer be connected to this engine? If so, where on the engine do the tach wires connect? I have read where some control boxes have a three prong plug below the friction bolt but mine does not. The engine is a transplant into a boat that previously had a much newer Honda with a tach and I would like to have a tach if possible.

Also, can a voltmeter be connected to the engine?

 

[dazk14]

What is the specific control box you have or post a pic. the grey lead is the tach lead and it, along with a voltmeter need a ground and switched +12 normally available in the control box. are the controls already mounted? other ways to do it as well.

 

[David Young]

I have the same model number motor as you do. I have a tach but I think it came with the boat when it was new in 1977.

 

[ezmobee]

dazk14 is right. Should be a grey wire in your control box which is the the tach pulse feed. There should also be a purple wire in there which is the switched +. There isn't a plug in deal on your vintage but the wires should be in there. I added one to my '73 years ago.

 

[fabieber]

Thank you gentlemen.
The controls are mounted and "ezmobee" you are correct - there is not plug in. I will take the controls apart to look for the wires you describe.
To that end, it raises another questions regarding gauges.
- I had to put a new ignition switch in as the key for the original was lost. It does not seem as if there is just an "on" position on the new switch. The first movement of the key energizes the starter and unless I ever so slightly turn the key back to the left, the starter remains engaged. I moved the wires one at a time from the original switch to the new one but wondering if the letters on the two switches are identical in what they mean. I realize this is a bit off topic but since I have to take the switch apart to find the grey and purple wires I thought I would ask for your opinions regarding my switch issues.

Also, would you mind reflecting on the voltmeter connection as well?

 

[ezmobee]

A voltmeter can connect to the switched + as well (the purple wire as well).

That ignition switch sounds suspect. It should definitely have an off, on, and momentary start positions.

 

[fabieber]

Regarding the switch being suspect, is it possible that one or more of the wires is not connected to the correct terminal?
If all weren't properly connected, would the switch still engage the starter and turn the engine off?

 

[fabieber]

I opened the controls, found the grey wire, ran a temporary lead from the grey to tach pulse, purple to the tach ignition and grounded. Voila....tach worked. That was two days ago.
Today I ran the permanent wiring with connections as described above and the tach needle did not move. Then suddenly the needle began climbing (engine at idle) pegged out at 7,000 rpms and stayed there.
I moved the setting on the back of the tach to every available spot but nothing changed.

I took a volt meter reading on the purple wire (at the controls) and only read 6.7 volts. Checked the sender wire (didn't know what I should get) and got a <-2.7> reading. I also hooked he ignition wire to the voltmeter and no movement of the gauge.

I would be so appreciative if you guys could tell me what to do next. Wondering if I messed up the tach somehow and also wondering why the voltage reading is so low on the purple wire.

 

[Strangeleak]

You must have a break, short or poor connection/corrosion in the purple wire. Or the ground you've chosen is poor. Clean all connections thoroughly.

Sender wire carries pulsed AC voltage which can't be accurately read without a multi-meter capable of peak/hold readings.

Not sure about the tach setting on that engine though.

 

[Strangeleak]

After some research it looks like the tach setting should be 6.