Need wiring for Motorola tach

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sc2dave
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Need wiring for Motorola tach

Post by sc2dave »

I have a Motorola low rpm tach that i need a wiring diagram for. The part no. is 7ATH24042. It goes up to 40000rpm and it also has an hour meter. It might be for a boat or 18 wheeler. One of the threaded studs is PI, another is B+, GND, SIG. It also has 2 wires coming out, 1 is Brown, another is Yellow. I hooked up power to B+, ignition tach wire to SIG, and ground to GND.Nothing happened. A sticker says ALT/HOUR/TACH. I'm wondering if one of those wires also has to be hooked up with power in order for it to work.
superpursuit
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Re: Need wiring for Motorola tach

Post by superpursuit »

sc2dave wrote: Thu Oct 18, 2018 11:51 pm I have a Motorola low rpm tach that i need a wiring diagram for. The part no. is 7ATH24042. It goes up to 40000rpm and it also has an hour meter. It might be for a boat or 18 wheeler. One of the threaded studs is PI, another is B+, GND, SIG. It also has 2 wires coming out, 1 is Brown, another is Yellow. I hooked up power to B+, ignition tach wire to SIG, and ground to GND.Nothing happened. A sticker says ALT/HOUR/TACH. I'm wondering if one of those wires also has to be hooked up with power in order for it to work.
That's real funny there. 40,000 rpm is low rpm? Sorry, couldn't resist. :D

I would try to Google it or contact Motorola themselves for this info. Sounds like it may be an aircraft gauge with the ALT being for altitude.
sc2dave
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Re: Need wiring for Motorola tach

Post by sc2dave »

Ooops, didn't doudle check what I wrote. 4000 rpm
mag2555
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Re: Need wiring for Motorola tach

Post by mag2555 »

Your playing with Fire there!
Don't assume that because nothing happened when you hooked it that you did not harm any semiconductors that may be in the Tach!
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
grandsport51
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Re: Need wiring for Motorola tach

Post by grandsport51 »

It uses the alternator output as a signal to make it functional and is calibrated to the specific alternator
Seems like a hopefully inexpensive paperweight
Link attached for general info

https://youtu.be/pdkFqAsAcgY

Thanks
Dave B.
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