old ignition problem tach not working

[khybskid]

my

My stbd engine stopped running while out fishing. Got back to the dock with port engine. No spark!!! After dealing with old as dirt ignition i installed new elecrtonic ignition from sierra for big block chevy. Figured it all out but cant make the tach work now. I have the wire from the tach but it flutters in the zero range like its going backwards so i left it unconnected till i know what to do. Stbd motor runs well after sea trial

[h2ojst]

More than likely, the old ignition had the tach sender wire going to the coil negative. The newer electronic ignitions require the tach lead to go to a different wire. Read your ignition installation instructions or call their customer service tech person.

[khybskid]

Thanks for some good advice joe. Im going to look for that help now.

[khybskid]

I need someone to tell me how to get my tach to work with this new electonic ignition that replaced the old mercruiser distributor and thunderbolt ignition. Any one have this similar problen

[lobsta1]

If your boat had the original Thunderbolt 1 ignition, it's possible that Bertram modified the wiring harness to work with it, That's what my owners manual says they did on my 1978. My boat was converted to Mallory distributors & the tachs were way off. I installed new instruments on the bridge & ran new wires from the negative side of the coil to the tachs. My bridge tachs now read correctly at 3000 rpm while original lower helm tachs read over 4000 rpm.
Al

[khybskid]

Thanks for that info Al. I was hoping that there was some kind of switch,relay, converter or something easier than replacing and rewiring the tach.

[lobsta1]

Did you ever straighten this out? Did you try to run a temporary new wire from the engine direct to the tach? That will at least point you in a direction.
Al

[khybskid]

i have been out haddock fishing and havent taken the time to do that yet al. I just listen to the motors to sync them runs excellent with this new ignition. I have a diagnostics tach i was going to set up on it to see if it works I will let you know when i do try anything to fix it. Plus i have had a rush of people who are looking at the boat. Its still for sale for 13,500 but ive been using it more this year than past years.