Need advice/help with new Tachs that don't work with Thunderbolt Ignitions

[Tin Pangas]

I made the mistake of letting a so called marine electrician replace all of the guages on the flybridge. He can't gewt the new tachs to work and says it's cause the Thunderbolt ignitions take a special tach that is no longer made. He wants me to get new alternators so he can hook the new tachs up to them. There is nothing wrong with my alternators. I'm at my wits end.
I would like to find someone willing and able to do the job. Any advise is greatly appreciated.

 

[kindafishy]

http://www.offshoreonly.com/forums/general-q/234009-thunderbolt-ignition-tach-wire.html

 

[bman440440]

if he is trying to get you to do that he is trying for more $$ out of you... just hook the tack up to the negative on the coil and your good to go!

 

[Tin Pangas]

i saw that forum response and many replies of hook it up to negative on the coil. Problem is...my Thunderbolt coil is encapsulated in a switchbox (# 332-2986A22) and I just spent the day with Marine Electrician #2 and still couldn't get modern tachs to work. I can hook the ancient 'Thunderbolt tach' back up that reads inaccurately, but reads something where any modern tach just simply doesn't read. Should I just resign myself to buying new alts and hooking the new tachs to them?
I know that my fix is probably similar to the outboard fix of hook it up to the neg on coil but my inboard 454s have that switchbox. Any help here is tremendously appreciated. I would owe somebody bigtime if they could help me with this one!

 

[kindafishy]

what thunderbolt do you have, year & hp. inboard/ outboard

 

[Tin Pangas]

MERCRUISER (330 MIE GM 454 V-8 1977-1980) sERIAL NUMBER RANGE 4623115 - 5889913

 

[kindafishy]

https://faria-instruments.com/products.php?calledGauge=1_tach

how about a tach with a magnetic pick up? looks like those alternator tachs need to be calibrated to your engine with a existnig, working tach.

 

[bus kid]

maybe upgrade your switch box if its cheaper then 2 new alts.

http://www.marineengine.com/newparts/part_details.php?pnum=CDI114-2986

 

[bman440440]

you still have a coil on your motor don't you?? the negative lead on that is what you hook your tack to.

 

[kindafishy]

or go full on redneck and use a timing light to provide signal to the tach.

 

[JUST-IN-TIME]

Grey wire is all u need

What tach are u running, the grey wire comes off wire harness by throttle controls or trim switch