Factory tach
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More Turbo
Joined: May 2008
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Factory tach
I'm sure this has probably been discussed before, but I'd like to add a factory tach to my '84 F-250. I have an instrument cluster with a tach already so that part is already out of the way, but I have a few questions:
1. Is the instrument cluster harness already wired for the tach since it was an optional accessory, or will I need to add a pin to the plug?
2. I'm currently using a Sun mini tach with a MSD 6AL ignition system. The tach is connected to the tach output terminal on the side of the MSD since you cannot connect a tach to the negative terminal on the coil with a capacitive discharge ignition. I don't think this will be an issue since the Sun tach reads accurately so I would assume the factory tach would as well using this same terminal?
3. If the wiring harness is already set up for a factory tach, I'm assuming all I would need to do is connect the original coil negative wire to the tach output terminal on the MSD?
1. Is the instrument cluster harness already wired for the tach since it was an optional accessory, or will I need to add a pin to the plug?
2. I'm currently using a Sun mini tach with a MSD 6AL ignition system. The tach is connected to the tach output terminal on the side of the MSD since you cannot connect a tach to the negative terminal on the coil with a capacitive discharge ignition. I don't think this will be an issue since the Sun tach reads accurately so I would assume the factory tach would as well using this same terminal?
3. If the wiring harness is already set up for a factory tach, I'm assuming all I would need to do is connect the original coil negative wire to the tach output terminal on the MSD?
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Joined: Jul 2010
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From: Marysville, WA
So long as you didn't mess with the factory Duraspark plugs on the drivers fenderwell, there should be a 2 wire plug with a black and a dark green/yellow stripe wire. The dark green/yellow is the coil - signal wire to the tach. Run that to the MSD tach port. Hook the black to engine ground.
Also, when you pull the old cluster out, look at the connector. If there is a dark green/yellow wire in position 11 on the connector, the truck is wired for it. If not, run a new wire from the I connection on the back of the tach cluster to the MSD tach port.
Mine was not originally equipped with a tach, but I just swapped clusters, got the factory coil wires for the tach, plugged them in and it worked. The truck already had the wire in the main harness. Hopefully yours does too.
Also, when you pull the old cluster out, look at the connector. If there is a dark green/yellow wire in position 11 on the connector, the truck is wired for it. If not, run a new wire from the I connection on the back of the tach cluster to the MSD tach port.
Mine was not originally equipped with a tach, but I just swapped clusters, got the factory coil wires for the tach, plugged them in and it worked. The truck already had the wire in the main harness. Hopefully yours does too.
Posting Guru
Joined: Apr 2011
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From: Orlando area
I installed a factory tach in my '82. As long as you currently have the instrument cluster "with the gauges", the tach will plug right in. No additional wiring necessary. I also run the MSD 6a. The yellow tach wire off the MSD will work perfectly with the factory tach. The wire "to" the tach/instrument cluster is already in the engine wiring harness at/near the coil. You just need to find it and splice the yellow MSD wire into it (I don't remember the wire color now but I have a wiring diagram - maybe it's the green-yellow wire described above).
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More Turbo
Joined: May 2008
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Good info, thanks!
The factory Duraspark system is all there, its just disconnected. When I installed the MSD system I disconnected the Duraspark and taped the connectors. That way I always have a backup ignition so I don't get stranded. In case the MSD ever fails all I have to do is plug in the old module and hook up the coil.
I want to take apart the cluster to clean it and repaint the needles first so it may be a week or two before I get everything installed but I know what to expect now. Thanks.
The factory Duraspark system is all there, its just disconnected. When I installed the MSD system I disconnected the Duraspark and taped the connectors. That way I always have a backup ignition so I don't get stranded. In case the MSD ever fails all I have to do is plug in the old module and hook up the coil.
I want to take apart the cluster to clean it and repaint the needles first so it may be a week or two before I get everything installed but I know what to expect now. Thanks.
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