Tacky Tach Problem

[wil7483]

So heres the deal. I am in the process of restoring a 1988 Wellcraft Elite 222 XL and I have finally gotten to placing the new power plant into the boat. The boat was originally powered with an OMC system but I am converting everything over to a Mercruiser setup.

Anyway, while taking the old engine out I damaged the engine harness and had to replace it. I was able to get another harness end and splice it into the boats wiring harness. Once I got the wiring harness all spliced and connected to the engine, I try to start it and it cranks but won't start. I go over the wires, consult the manuals and everything looks good. I then start to systematically disconnect wires one at a time and crank it. Low and behold, once I disconnect the gray wire it cranks right up. The gray wire is the one going to the neg. (-) side of the coil. So although the engine starts, I have no tach or voltage readings on the dash. I've check the wire with the voltage meter and it shows no load going through it so I can't see where it is shorting the engine out when it is connected.

What could I be doing wrong or have done wrong? Could the gauges be wired incorrectly to cause this problem?

Help! !! !!!!

 

[Don S]

Re: Tacky Tach Problem

OBviously the engine was and 88 or 87 that came out but what was it 5.0, 5.7. 5.8 Ford, Chevy? ? ?
And what is going back in it. Specifically, year model and all the other good stuff.

 

[bruceb58]

Re: Tacky Tach Problem

Have you traced where the grey wire goes to on the dash?

Strange that you have no voltage readings. Sounds like a mis-wire when you rebuilt the harness.

A bad tach can also short out the ignition.

 

[wil7483]

Re: Tacky Tach Problem

I am sorry, the boat had a BB Ford 460 in it, I am replacing that with a SB Chevy 305.

The gray wire goes to the tach on the dash. I totally rewired the dash during the restoration. In all, I have probably totally rewired 90-95% of the boat with new wiring. This is the 1st problem that I have found during the entire wiring process.

I will go out again this weekend and test the wire with the multi-meter. I think what i did wrong was test it for a load in the start position but not while actually cranking it. If I find a current then I guess I will have to take the dash back apart and retrace those wires also and make sure something isn't touching that shouldn't be.

The restoration is available to see in the restoration section of iboats forums.

Thanks for the help.

 

[Don S]

Re: Tacky Tach Problem

All you have to do is a continuity test on the gray wire from the coil to the tach.
When I asked for model number, I was looking more for the Mercruiser Model or SN of your new engine so I could determine they type ignition system you have.
It's possible the OMC tach won't work with whatever ignition system you have now.

 

[bruceb58]

Re: Tacky Tach Problem

Does the wire go to the correct terminal on the tach? There are 3 terminals..one to 12V, one to ground and one to this grey wire.

When you disconnected the grey wire, did you disconnect it at the tach end or the coil end? The reason I ask is that if you disconnected it from the coil end it is possible there is a short to something between the tach and the coil.

 

[wil7483]

Re: Tacky Tach Problem

Hi again. The entire dash is new, the gauges are all new Teleflex gauges. None of the original OMC stuff remains in the boat.

Maybe there was some confusion earlier in the post. I had to splice a new wiring harness end onto the old harness due to damage. I m talking about the piece that plugs into the engine wiring harness. The harness wires all match up perfectly, same colors and same operation as the original harness. I will try to get a picture of what I mean to post. The problem is that the gray wire is shorting out the engine for some odd reason if it is connected.

See that plug that plugs into the engine. Well it had to be replaced, so I just spliced a new one on.

 

[Don S]

Re: Tacky Tach Problem

As bruce mentioned earlier, a defective tach will kill the engine. And trust me, new things can be bad right from the beginning.