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Help with tach wiring

Gerbow

Sr. Member
Joined
Jul 24, 2011
Messages
775
Loc.
Jacksonville
I picked up a tach and it says to splice red wire into any vehicle harness wire which is energized with the battery voltage ONLY when ignition key is in the ON (run) position. So, it seems everything is on in ACCESSORIES also.
Where should I splice into?? Also, should I ground it to the battery neg. terminal or is grounding to the frame/body under the hood ok?
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,835
Powering the tach off accessory will be fine.
And doesn't need to go to the battery, and the frame is generally the worst ground on a Bronco. Just ground it to the dash.
 
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Gerbow

Gerbow

Sr. Member
Joined
Jul 24, 2011
Messages
775
Loc.
Jacksonville
Its a '72 with 302. Im fine with wiring to accessories but directions say "DO NOT" do this.
 

Explorer

Bronco Guru
Joined
Mar 2, 2008
Messages
4,390
Loc.
Raphine, Virginia
Standard tach wiring diagram below. Don't quite understand wiring to accesory position of switch. Should be to run side of ignition switch.
 

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Gerbow

Gerbow

Sr. Member
Joined
Jul 24, 2011
Messages
775
Loc.
Jacksonville
Standard tach wiring diagram below. Don't quite understand wiring to accesory position of switch. Should be to run side of ignition switch.

Thats better than whet Ive been looking at. So I can just splice into wire under dash from run side of ignition switch? (going to engine?) would you grund to battery terminal or under dash. Directions say best to terminal for best tach performance.
 

Explorer

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Mar 2, 2008
Messages
4,390
Loc.
Raphine, Virginia
I've alway's grounded to dash making sure it's a good clean ground. Dash is mounted to firewall and firewall should be grounded to engine.
 

Explorer

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4,390
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Raphine, Virginia
Basically anything hot in run position of ignition switch. Like the radio etc. Everything hot in ACC is hot in run position. Exception being actual ignition wire is hot only in run and start.
 
Last edited:

Steve83

Bronco Guru
Joined
Jul 16, 2003
Messages
8,981
Loc.
Memphis, TN, USA, Earth, Milky Way
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Pull a new wire (DkGn) from the coil (-) to the tach input. Splice tach power to Bk/Gn at the ig.sw. or ICVR. Splice tach illumination into any LB/R at the instrument cluster or dash. Connect tach ground to the dash or instrument cluster shell.
 
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Gerbow

Gerbow

Sr. Member
Joined
Jul 24, 2011
Messages
775
Loc.
Jacksonville
Watchin football with my boy today. Gonna get on this 2moro. Hopefully I have it now. If not, I'll be asking again. I was just mostly concerned with the one above mentioned wire.
 
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