Electrical Tach Problems

[mxp01]

As you all know i have changed my alpine from Positive earth to Negative earth. My Tach was positive earth, I received the instructions on how to convert it over. Once the tach was converted i did the next step, i changed the loop of wire in the plastic coil. Now when i start the engine the tach starts to move slightly, when i rev the engine the tach just jumps around. (keep in mind the the car has an alternator now) if that has anything to do with anything. Any thoughts??

 

[Tom H]

Mike, Cade,

First step is be sure you have the metal U shaped piece installed inside the loop. That is the loop of wire must go around the metal. And the metal must be iron or steel- not aluminum or copper or brass. Next be sure the end of the metal piece makes contact -at both ends- with the little tips of metal you can see on the inside of the "transformer" the part that is mostly inside the tach housing. The metal piece outside mates to the metal piece inside and that forms the iron core of the transformer that couple the pulse from the white ignition wire to the electronic pulse meter inside.

Next try reversing the direction of the wire. Actually reversing the direction of the current through the transformer. You can accomplish that by undoing the loop and re-winding it in the opposite direction. Or keep the loop as is but change the ends so that the end that was connected to the coil is now connnected to the ignition switch. Might be the easiest way to try it. And if that works then re wind it. Almost surely you need to reverse the loop from what it had been since you now have reversed the polarity of the ignition

Lastly you might try looping the wire one extra loop.

Tom H

 

[mxp01]

Thank you Tom, I'll give it a try.

 

[Tom H]

Good, And let us know how Granddad made out on repairing the ammeter.

Tom

 

[Ken Ellis]

Mike and Cade,
Did the tach work before polarity was changed on the car?
Did you run the car in neg ground configuration while the positive ground tach was hooked up?
(You can probably see where I'm goin' with this...)

Ken

 

[lgurley]

negative earth

If anyone has complete instructions to change to negative ground I would like a copy. My SV has an alternator and is positive ground. I was told SV only came in negative earth. I get lost in electricity.
If anyone can help me my e-mail is larry@crossroadstrans.com

 

[Tom H]

Larry,

Here's a link to the site that Mike used ( I think) . I found it by doing a search for "tach" on this forum:

The article is pretty complete:

http://www.lotus-cortina.com/electric/convert.htm

Originally posted by Wombat.

Tom H

 

[mxp01]

Ken, The Tach worked great before the change. When I changed the polarity I discounected the Tach ( the Tach Never was hooked up after the change was made, I made sure of that ). By the way I have not had time to do what Tom Suggested earlier in this post. the Tach "Tries" to work, so I think its fine, from what Tom has said I think its with that little coil in the back. I Do have the Original peice of metal that goes around the plastic peice. The Ammeter works. Sometimes right when the car is started and I tap the gas the needle will go all the up above 30+ and get stuck, But with a tap of the glass it comes back and works fine until the next startup.

 

[Tom H]

Oh, and by the way. You'll note a critical piece of information missing from the article. It makes reference to the white ignition wire looping through the "plastic holder" and about changing the directiion of that wire looping through the plastic. What the article fails to say is that the METAL piece around the plastic loop is critical - ya gotta have it and it's gotta be iron or steel. In fact the metal piece is shown in the top photo installed on the tach - you can see the round knurled nut holding it to the curcuit board. In the second photo, that part is not shown, but you can see the two tips of the inner half of the transformer (to the left and right of the mounting post for the clip). These tips must make contact with the matching tips on the external metal clip.

The inner metal part and the outer metal part form the iron core of the pulse transformer that couples the signal from the ignition wire into the tach.

Tom H

 

[Ken Ellis]

Mike and Cade...
That's good news on both counts. We'll wait for your report on Tom's suggestions.

Good luck!
Ken

 

[mxp01]

The Tach works again, thank you Tom. The problem was the metal peice that went around the coil. It was not making good contact with the other side of the Tach. I took care of that and it works great now. Thanks for everyones help on this.

Cade Pennell