Sun tach sending unit - Impala Tech
Electrical & Wiring Troubleshooting electrical problems

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post #1 of 4 (permalink) Old 12-09-2014, 04:20 PM Thread Starter
Join Date: Apr 2014
Location: New York
Posts: 55
Sun tach sending unit

Hi everyone. In my '62 SS, I'm running a factory Sun tach and sending unit. The sending unit takes 2, 1.375 volt mercury batteries which are no longer available. I know these units can be converted over with modern electronics to eliminate the batteries. I've gotten prices to do this conversion from $265.00, which I thought was a lot, to $350.00 which I feel is outrageous and would never consider. I searched on line but couldn't find the exact voltage that I need. I did find double AA alkaline and lithium batteries at 1.5 volts each. Is anyone still using these factory units, and if so, did you convert or find another battery source?? I don't mind changing the batteries every few years but I don't want to damage the sending unit with more voltage. I can't see how .250 more volts, between the 2 batteries, would hurt anything. When I took my sending unit apart, it had 2, 1.5 volt Duracell Procell batteries, that someone had installed. I only ran the motor a short time before removing it, and the tach seemed to work fine. Any suggestions would be appreciated. Thank you, Carmine.
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post #2 of 4 (permalink) Old 12-09-2014, 06:26 PM
Join Date: Jan 2007
Location: Lewisburg, Ohio
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I know you want to keep the old tach. But if it were me Id replace it with something newer.
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post #3 of 4 (permalink) Old 12-09-2014, 06:55 PM Thread Starter
Join Date: Apr 2014
Location: New York
Posts: 55
Yes, I do want to keep it, and having it "modernized" is probably the way to go, just a lot of money.
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post #4 of 4 (permalink) Old 12-09-2014, 07:16 PM
Join Date: Jan 2006
Posts: 13,022
They are just going to put new tack in your old case. The Mercury batteries were discontinued because of the mercury getting from land fills into the water supply. You can use any battery you want and solder in a resister into the supply wiring to reduce the voltage, but to size the battery you need to know the amperage rating of the battery which I can not find using a quick search on line. I can easily find the amperage capacity of button batteries that are still made but not the old mercury cell. It wouldn't take a lot of OHMs to nock the voltage down as the batteries are so weak (compared to the power rating of a lead acid car battery).

Big Dave
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