Need help with tachometer install

I'm having problems getting a tachometer to work on my 1045A2. It has the 200 amp alternator and I'm hooking up the signal wire to the AC post, yet getting no movement on the needle. I have the same exact tachometer on my LMTV and it works fine when installed there, so the tachometer is good. I'll try to explain each picture below.

Tach is exactly like this one, single signal wire, and works fine when hooked up here on my LMTV.

Here is the 200 amp HMMWV alternator showing the AC post for signal hookup. With engine running, I get 13.3 volts AC.

Here is the LMTV alternator, AC post voltage reads 13.7 volts AC and the new tachometer works fine hooked up to it.


Any suggestions or ideas? According to this, it should work fine with the signal wire driven from the yellow AC post

View attachment Tachometer-A2.pdf

2 types of Hmmwv tachs...Buss bar one connects to the tach drive on NA motors, and round connector type connects to Alternator.

What Greg said...use the Tach drive off the back of the motor, oil pressure gauge tap for power.
the pic of the instructions you posted are of the cannon plug A-pillar mounted Tach, that’s not what you have.

Retiredwarhorses said:

What Greg said...use the Tach drive off the back of the motor, oil pressure gauge tap for power.
the pic of the instructions you posted are of the cannon plug A-pillar mounted Tach, that’s not what you have.

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Tried it today; no luck. I'm not getting any type of reading off of either wire with a DVM.

there are 5 wires to hook up
first is key on power- spliced off the power feed on fuel gauge
second is ground- connected to back of instrument gauges gound
third is light-spliced off of instrument gauge light feed
the next 2 wires are signal feed wires for the pulses,the tach drive in the rear of motor is where they hook too,it does not matter which goes where,they are just pulses and work the same if reversed
hour meter count engine running time
it would not work hooked up to

My tachometer only has 1 signal wire terminal.

Andyrv6av8r said:

My tachometer only has 1 signal wire terminal.

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Can’t help you on that Tach...I only use the hmmwv specific Tach....

Retiredwarhorses said:

Can’t help you on that Tach...I only use the hmmwv specific Tach....

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Understood. I was hoping with this thread that some electronics guru could explain the differences in the alternator AC outputs between the two trucks.

Andyrv6av8r said:

Understood. I was hoping with this thread that some electronics guru could explain the differences in the alternator AC outputs between the two trucks.

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I know this is an old post but did you ever get this figured out? The tach I'm trying to hook up only has a single wire signal input.

Jessmillx1 said:

I know this is an old post but did you ever get this figured out? The tach I'm trying to hook up only has a single wire signal input.

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I ended up ordering a different tach and it has been working fine.

Search for this on Ebay

M998 HMMWV HUMVEE BRAND NEW TACHOMETER Gauge 12469030