1973 115HP tach question

[ErikF]

I picked up this outboard last week and have been working on getting it running on my boat, an 18' Blue Fin Sea King, I have the motor bolted up and running but when I get out on the lake I feel like it's not getting up to full RPM. The outboard came with a tachometer that looks like it wires in with two wires, I've consulted my Clymer's shop manual and going off the wiring diagram it looks like this might be correct with one wire being signal and the other being ground. I have two wires coming out of the control box that I believe had been hooked up to the tachometer, I connected these wires both ways with the engine running and got nothing registering on the tachometer.

That's the extent of my messing around. What's the next step? Where does the tach signal come off the engine? Pictures are appreciated as I'm not too sure of myself looking at the wiring diagram. What do I need to do to test the tachometer itself and the wiring on the engine side?

Any advice is greatly appreciated. I'm planning to buy a TinyTach for this engine and other projects but would love to get this gauge going to complete my dash panel or at the least definitively test it bad and get rid of it!

Thanks,

Erik

 

[Haffiman]

Re: 1973 115HP tach question

It should be 3 wires.
B+, Neg (ground) and signal.

 

[emdsapmgr]

Re: 1973 115HP tach question

Most modern outboard tachs use a 3 wire system, plus one for the light. Very old (mid-70's) Airguide boat tachs used a 2 wire system. (Those old tachs were very accurate-jeweled movement.) Possible your boat was setup for that type tach. You will find one of your two existing wires is attached to a grey wire inside the control box. That wire was put in at the factory and was the signal (S) wire to drive the tach. If you use a more modern tach, you will need to find a pos and neg for the other two hookups. (plus the light-if you choose to connect it.)

 

[Haffiman]

Re: 1973 115HP tach question

If an old Airguide, go here:
http://www.classicboatwork.com/classicparts/gauges/airguide/Tach/airtach.html

Perhaps you may get a copy of the installation manual.

 

[ErikF]

Re: 1973 115HP tach question

Hello Again,

It's an Airguide gauge.

At the top of the frontside it says "P 6487" "4788" is on the edge of the backside, and "4GC" is written in yellow near the input wires.

Visually it looks identical to the model 666 A listed on the Classic Boat Work site.

Are there any simple tests I can do to verify whether or not the tachometer is working?