Tachometer not working

[Ron Brassord]

One by one, I have been fixing the problems in my recently acquired 1988 C30 caused by neglect. I have been very happy with the boat generally, and the problems have mostly resolved. Since buying the boat in July, the tack has not functioned. The hour meter does work.I got the U 25 xp cleaned up and running great.  The alternator did not have a tack wire on it, and I found the end of the original tack wire laying in the bilge. The previous owner evidently installed an automotive alternator without the wire. I bought a new higher amp unit, and had the wire installed. I tested the red wire to make sure it was the coming from the back of the tack, and it is. However, I get no response running the engine, and the rpm needle is still non functioning. When I turn on the key, the rpm needle does jump to 3000 rpms, and is peged there until I turn off the key, and it returns to zero. Question, do I go for a new tack? Any other test I can run? Is this tack repairable? I looked at the Torreson parts list, and it shows a replacement cost of over $350? Marine stores have tacks for under $100? Someone suggested a "Mighty Mite" which takes a reading off an injector feed line at $70? I'd like to stay original if possible and use the same hole and wiring, but not at $350. Anyone had and resolved this problem? Good sailing Ron B

 

[David Ladd]

recheck the wire to the tach from the alt

Hi,I am not an electrician, but I have worked on getting my tach to work and I have made some mistakes with ground wires. Its sounds to me that if the tach immediatley pegs to 3000 as you say when the switch is on that you may want to recheck which wire you have connected to the tach. There is an AC tap on the alt which should be going to the tach. If by chance that wire is grounded or you have the wrong wire going to the tach that would be the indication you have. Under normal conditions, when you turn on the switch the RPM needle should stay where it is until it comes up with the correct RPM or it should float down to zero until it comes up. In any case something is grounded that shouldn't be.

 

[J. Tesoriero]

Could be ......

Could be a mis-match between the type of tach and the RPM sensor on the engine. There are tach's that sense RPM's directly from a number of different engine sensors (magnetic, etc.)and there are tach's that run off the alternator. It is not clear from your post, what kind of tach you have. In addition, assuming you have a tach that will run off the alternator, when you upgraded your tach to a high output, the new alt. may have a different number of "poles" than the original - thus giving a different output signal to the tach. You would need to re-calibrate the tach to conform to the output signal from the new alternator. There should be an adjustable calibration setting on the tach but you will need to know the correct engine RPM. You can borrow an RPM tach strobe from your yard or use the old fluorescent bulb technique. I can give you the details in another post - ask if you need them.

 

[Ron Brassord]

Tack not working

I would think the original tack in my instrument panel worked off the original alternator, and it should work off a new alternator? The new alternator was specifically wired by a professional with a "tack" wire. I agree the higher output alternator might give a different reading and an adjustment is needed, but there is no responce at all in the tack.  West Marine lists two "alternator" tacks for $90 and $190. Is my next step to just purchase one and hook it up and hope? I haven't found any source to test and or repair the original. I cruise my C30 at 5 knots and the engine seems to be at about 2/3rds throttle,and the engine not straining, and very smooth, but, what rpm? I can't believe I am stessing the engine, but it would be nice to know for sure the actual rpm. Ron B