FAQ - Factory tachometer installation
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Post Fiend
Joined: Dec 2007
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From: Lost
Just to clarify some things.
A: 1980 is a one year wonder for instrument clusters. If you are going to do the job right you need to find another 1980 to get the correct printed circut from it, or buy a new printed circut for a 1980. There are some aftermarket ones avaliable. The gauges the tach and the speedometer itself are swappable 1980-1986, but the printed circut is 1980 only.
B: The Tach Swap will only work with trucks with ammeter and oil pressure gauges. All the wiring is already there in the cluster connector. Plug and play. If you have a truck with idiot lamps, you will have to do excessive rewiring to make it work. The entire main dash harness and engine harness is different between the two. The Ammeter Shunt is the most important difference. Without this factory shunt, full altenator charging amps (60 amps or more) will go through the ammeter gauge which is only rated at .5 amps causing fires.
C: Both Fordzilla80 and 1986F150six are correct. The tach gets it's signal from the tach test lead of the coil. So everytime the coil fires the tach gets a signal from it. It also gets power from the battery. On a V8 there are two grounds that go to the tach, on a six there is only one ground.
As you say, the firing of the coil on the V8 is more often than the I6 at the same RPMs. The extra ground on the tach error corrects the difference internally of the tach.
So to wire the tach without changing your printed circut.
1: B post on tach goes to battery power.
2: I post goes to the tach test lead of the coil
3: G is the main ground for the tach. (This has to be grounded)
4: 8 is only grounded on a V8 engine.
A: 1980 is a one year wonder for instrument clusters. If you are going to do the job right you need to find another 1980 to get the correct printed circut from it, or buy a new printed circut for a 1980. There are some aftermarket ones avaliable. The gauges the tach and the speedometer itself are swappable 1980-1986, but the printed circut is 1980 only.
B: The Tach Swap will only work with trucks with ammeter and oil pressure gauges. All the wiring is already there in the cluster connector. Plug and play. If you have a truck with idiot lamps, you will have to do excessive rewiring to make it work. The entire main dash harness and engine harness is different between the two. The Ammeter Shunt is the most important difference. Without this factory shunt, full altenator charging amps (60 amps or more) will go through the ammeter gauge which is only rated at .5 amps causing fires.
C: Both Fordzilla80 and 1986F150six are correct. The tach gets it's signal from the tach test lead of the coil. So everytime the coil fires the tach gets a signal from it. It also gets power from the battery. On a V8 there are two grounds that go to the tach, on a six there is only one ground.
As you say, the firing of the coil on the V8 is more often than the I6 at the same RPMs. The extra ground on the tach error corrects the difference internally of the tach.
So to wire the tach without changing your printed circut.
1: B post on tach goes to battery power.
2: I post goes to the tach test lead of the coil
3: G is the main ground for the tach. (This has to be grounded)
4: 8 is only grounded on a V8 engine.
I had just located the wiring info to not have to make changes in my current cluster. Think I'll go this route, and use a 3-4 wire plug, it can be unhooked to pull the cluster out. Trailer wiring plugs are cheap........
I wasn't really keen on swapping the entire cluster, since all my gauges work, and I've learned to trust them in the nearly 13 years I've had the truck.
I also wasn't too keen on adding an aftermarket tach, when the factory tach fits without getting in the way.
Posting Guru
Joined: Jun 2002
Posts: 2,091
Likes: 3
From: Suffolk, VA USA
Does it go directly to the battery, or through the IVR? If through the IVR, there will be a voltage difference.
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Post Fiend
Joined: Dec 2007
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From: Lost
I would assume it goes to a 12V (switched) rather than IVR, since the coil is running off higher voltage than the IVR.
Logistics Pro
Joined: Jun 2008
Posts: 4,990
Likes: 6
From: Florida
I only meant there's not a difference between the tachs that I'm aware of.Not that there's no difference between 6 and 8 coils.
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Post Fiend
Joined: Dec 2007
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From: Lost
Well, in this case, both items are the same.
I was simply pointing out that somewhere there had to be a difference in how they were wired, to account for the difference in firing cycles of the coil. Aftermarket tachs usually have a "4/6/8" switch to recalibrate for the various uses.
Wanna really get confused? I've got a car that has a rotary engine. 2 combustion chambers, 4 spark plugs, and 3 coils/ignition modules. It's complex, this is simple.
I was simply pointing out that somewhere there had to be a difference in how they were wired, to account for the difference in firing cycles of the coil. Aftermarket tachs usually have a "4/6/8" switch to recalibrate for the various uses.
Wanna really get confused? I've got a car that has a rotary engine. 2 combustion chambers, 4 spark plugs, and 3 coils/ignition modules. It's complex, this is simple.
Cargo Master
Joined: Mar 2008
Posts: 2,568
Likes: 207
From: Washington
More good info and pic on "do it yourself wiring". Read the last few posts for new photos.
https://www.ford-trucks.com/forums/9...4-f-150-a.html
Jim
https://www.ford-trucks.com/forums/9...4-f-150-a.html
Jim
Thread Starter
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Post Fiend
Joined: Dec 2007
Posts: 8,521
Likes: 16
From: Lost
More good info and pic on "do it yourself wiring". Read the last few posts for new photos.
https://www.ford-trucks.com/forums/9...4-f-150-a.html
Jim
https://www.ford-trucks.com/forums/9...4-f-150-a.html
Jim
It would be nice if that one pic showed the connection for the coil wire better, but I get the jist of it.
I guess I need to look for that connector by the DS2 box.....
Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
As for the wiring, if your truck has gauges, the wires are all there at the cluster connector that you need to make this work. Shouldn't have to get into the engine compartment at all.
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Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
The 1980 printed circut is Green, is the only difference with the above picture.
1981-1986 are color coded red. (I've seen some have faded to an off brown)
Makes them easier to spot in the wrecking yards.
1981-1986 are color coded red. (I've seen some have faded to an off brown)
Makes them easier to spot in the wrecking yards.
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Post Fiend
Joined: Dec 2007
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From: Lost
There was a mention of repinning the wire connector from the 80 to fit the 81-86 printed curcuit. Anyone got details on the wires that need to be relocated?
If it's just a couple wires that must be swapped, it may be better go this way.
If it's just a couple wires that must be swapped, it may be better go this way.
Logistics Pro
Joined: Jun 2008
Posts: 4,990
Likes: 6
From: Florida
Hopefully that helps anybody looking for pics of the difference between tach/non-tach trucks and 1980/1981-1986 printed circuits.
Do we even have a sticky on factory tach swaps?
Thread Starter
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Post Fiend
Joined: Dec 2007
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From: Lost
If there's one up there, I didn't see it....
Posting Guru
Joined: Jun 2002
Posts: 2,091
Likes: 3
From: Suffolk, VA USA
Ok...I've gone over this 5 times. At first I thought it couldn't be this easy, but it really is. There are only two pin swaps you need to make the 81+ gauge cluster work in an 80. Move the Light Green/White wire at pin 17 to pin 18, and the Dark Green/Light Green wire at pin 18 to pin 17. That's it. Everything else matches up. The pin moves themselves are pretty easy. If you look at the face of the plug, you'll see small plastic tabs that hold the wires in the connector. Use a precision screwdriver, gently pry the tab back, and pull the wire out. Shouldn't take more than a minute to make these two swaps.