Key on 12v power

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Jul 22, 2020 | 06:58 PM

Grandpa's66

Thread Starter

Mountain Pass

Joined: Apr 2018

Posts: 104

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Key on 12v power

I have a tach hooked up to my MSD 6A box and it doesn't seem like it's reading quite like it's supposed to. Giving a quick and heavy blurp on the throttle barely makes the needle move up to about 2000 but it seems like it revs up more than that. It is an Equus, budget option from Autozone so that may explain it, but I want to make sure that I'm getting a good 12v constantly if that makes a difference. I have the 12v power in and the light hooked up to the ACC post coming out of the ignition switch. I do have an EZ wiring fuse box with some extra circuits available if I need to switch it to something else, but just want to make sure that the ACC post is a good constant 12v (again if that makes a difference).

Jul 22, 2020 | 07:56 PM

Thunderkiss1965

Fleet Mechanic

Joined: Jun 2019

Posts: 1,899

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From: Southern California

On the back of the tach there should be a switch labeled 8-6-4. Make sure it is in the 8 cylinder position. Unless you have a six-cylinder, then it should be on the six. ;-)

Jul 22, 2020 | 08:41 PM

Grandpa's66

Thread Starter

Mountain Pass

Joined: Apr 2018

Posts: 104

Likes: 1

Quote:

Originally Posted by Thunderkiss1965

On the back of the tach there should be a switch labeled 8-6-4. Make sure it is in the 8 cylinder position. Unless you have a six-cylinder, then it should be on the six. ;-)

Thanks for the reply. I completely forgot about that but went and checked and it is in the 8 cylinder position. Thanks though great thought

Jul 24, 2020 | 04:00 PM

chiefdave

Tuned

Joined: Oct 2011

Posts: 312

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From: Warsaw

I have always used the accessory terminal for powering every thing except the ignition. Key on run for the ignition only. Some ignition systems don't play well with other accessories and will only work properly with a dedicated power source. Once had a truck that I could drive or listen to the radio but not at the same time until I switched the radio to accessory power.