Did I fry my tach?

MoaByte

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Dec 13, 2014
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Moab
 
I installed Holley Sniper late last winter along with a desmog surgery. I didn't hook up the stock tach as the LCD screen from the Sniper has a digital one. I was going to send my distributor for recurve but couldn't leave the truck sit, so I stabbed a HEI until in there.
AC wasn't working, but if I ran a jumper wire from the compressor to the battery, it worked.
Found out that the tach wire needs to be connected for the AC amp to send power to the compressor.
Okay, so I woke up this morning, drank a cup of coffee and proceeded to hook the black tack wire to the tach signal wire that goes from the HEI (coil -) to the Sniper (Or so I thought). Started the engine. Tach isn't working, compressor doesn't engage.
Take another look and notice I hooked the tach to the switched 12v from the ignition switch.

Hooked the tach wire to the right wire and tried again. Still no tach, no compressor engagement, engine still runs. WTF? Now what?
 

Seth S

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Jan 4, 2011
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Vermont
 
From the 85 wiring diagrams:

1589825192641.png


Looks like Black -Yellow Stripe wire is power from the ignition switch and Black is neg coil through igniter to Tach

1589825365005.png
 
Last edited:

MoaByte

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Dec 13, 2014
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Moab
 
Thanks Seth. These are the connections on the passenger side fender well that went to the coil. FSM says it was the black wire, but attempting to read a PDF on my phone about gave me an aneuryism. Honestly, I lose understanding of circuits looking at diagrams. Didn't help that I left my multimeter at work.
 

MoaByte

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Dec 13, 2014
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Moab
 
The VSV doest work with the EFI. Would it hurt to connect the compressor to the VSV wire?
 
Joined
Nov 25, 2014
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Western victoria Australia
 
The VSV doest work with the EFI. Would it hurt to connect the compressor to the VSV wire?
Probably not wise. The vsv wire is pretty thin. If you must, a relay would be advised.
edit strike that. I read it as activating the comp from the vsv wire.
Activating the vsv from the comp clutch would be ok.
 

MoaByte

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Dec 13, 2014
Messages
513
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Moab
 
Just to follow up. I believe the tach is fried. I got the AC to work by cutting the diode out of the AC amp circuit board per the FAQ. Thank you @TrickyT
 
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