Tach power mess
Thread Starter
|
Senior User
Joined: Jun 2012
Posts: 164
Likes: 0
From: TN
Tach power mess
As the title lists, my tach is all messed up. I installed this tach myself (as it didn't come factory with one.)
First things first... My truck:
1980 Ford F250 351M
Gague cluster has oil and battery gague, not lights.
I installed it using this guide.
I've read this thread: Tach is All Caddywhompus: Repair
Cleaned the browning glue, it seemed to help... a little.
Checked all connections between dash and tach test off the ignition coil, everything is fine.
Here's what I believe to be the problem:
The red circle is the +12v power source. When I have the wiring harness connected, it bounces between 8v and 11v. When I disconnect the harness, and test just the harness to the ground, it goes back to just 12v.
If I bypass the 12v on the harness to another 12v power source, the tach works perfectly fine. So I ask all of you, any ideas to why as soon as I connect the cluster the 12v jumps between 8v-11v?
By the way, feel free to steal the picture for other forums, I couldn't find an exact one for the 1980 printout so it took me a few tries to get it wired correctly.
First things first... My truck:
1980 Ford F250 351M
Gague cluster has oil and battery gague, not lights.
I installed it using this guide.
I've read this thread: Tach is All Caddywhompus: Repair
Cleaned the browning glue, it seemed to help... a little.
Checked all connections between dash and tach test off the ignition coil, everything is fine.
Here's what I believe to be the problem:
The red circle is the +12v power source. When I have the wiring harness connected, it bounces between 8v and 11v. When I disconnect the harness, and test just the harness to the ground, it goes back to just 12v.
If I bypass the 12v on the harness to another 12v power source, the tach works perfectly fine. So I ask all of you, any ideas to why as soon as I connect the cluster the 12v jumps between 8v-11v?
By the way, feel free to steal the picture for other forums, I couldn't find an exact one for the 1980 printout so it took me a few tries to get it wired correctly.
Posting Guru
Joined: Aug 2009
Posts: 2,271
Likes: 2
From: Mexia, TX
Have you put another load on that wire that's seeing the voltage drop? It could have some excessive resistance somewhere down the line that causes problems when something's trying to draw power through it.
On my 81 the 12v wire never worked when I installed my tach cluster so I just ran the tach off an add-on fusebox that I installed that comes on with the key (via relay).
On my 81 the 12v wire never worked when I installed my tach cluster so I just ran the tach off an add-on fusebox that I installed that comes on with the key (via relay).
Moderator
Joined: Nov 2007
Posts: 22,415
Likes: 92
From: Denver Metro Area, CO
First thing to come to my mind is the red-circled power source... if this is power from the ICVR then yes, I wouldn't be surprised if it varies.
I don't understand why all the soldered wires and hacking though, I'm not aware of anybody needing to do that just to get a tach to work.
I don't understand why all the soldered wires and hacking though, I'm not aware of anybody needing to do that just to get a tach to work.
Thread Starter
|
Senior User
Joined: Jun 2012
Posts: 164
Likes: 0
From: TN
The guide I listed in my original post showed it being soldered in (but on red printout.) The tach works fine, minus the power issue. I will check to see if putting a different load causes the same thing or not. If I don't use this pin for a 12v, is there a second one? I'd rather not have to put in a relay for this.
Moderator
Joined: Nov 2007
Posts: 22,415
Likes: 92
From: Denver Metro Area, CO
Trending Topics
Thread Starter
|
Senior User
Joined: Jun 2012
Posts: 164
Likes: 0
From: TN
I know they are, and I took precautions to make sure I did it right between the red and green printouts. It looks like it is just a wacky 12v wire, I'm going to just put a relay in to run my tach.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
Thread Starter
|
Senior User
Joined: Jun 2012
Posts: 164
Likes: 0
From: TN
Alright so I wired in a relay with the tach, it all works now except it reads about 300-400 RPM's too high. I wired both grounds on the tach to spec for the V8 checked the black ground next to the green signal wire under the hood to make sure it was grounded, any ideas? Search has no results!
Posting Guru
Joined: Aug 2009
Posts: 2,271
Likes: 2
From: Mexia, TX
Did it read that high when you powered it from another 12v source when you were previously testing it?
When I was first getting my tach working, I compared it to a Sunpro I had installed the year before, and I did notice there was a difference of 100-200RPM between the two.
What are you comparing it to to know that it's reading high?
When I was first getting my tach working, I compared it to a Sunpro I had installed the year before, and I did notice there was a difference of 100-200RPM between the two.
What are you comparing it to to know that it's reading high?
Thread Starter
|
Senior User
Joined: Jun 2012
Posts: 164
Likes: 0
From: TN
No but read the same with the alternative power source. I know it's running high because I have an rpm gague that runs off of the magnetic type tester you clamp over the no. 1 cylinder. Researching this it looks like you can adjust the needle by pulling it straight out to run lower or push it in to run higher, is this true?
Fleet Mechanic
Joined: Jul 2011
Posts: 1,916
Likes: 4
The only thing I would figure would make the tachometer's reading off would be the electrical connections.
On the 300-6 models, the wiring harness for the tachometer only has a single green wire. The tachometer isn't grounded, and this is what lets the tach read correctly for the 6 cylinders.
On the V8's, the tachometer needs to be grounded. If it isn't grounded, it will read higher for the V8's.
If yours is grounded correctly, then I don't know.
On the 300-6 models, the wiring harness for the tachometer only has a single green wire. The tachometer isn't grounded, and this is what lets the tach read correctly for the 6 cylinders.
On the V8's, the tachometer needs to be grounded. If it isn't grounded, it will read higher for the V8's.
If yours is grounded correctly, then I don't know.
Posting Guru
Joined: Aug 2009
Posts: 2,271
Likes: 2
From: Mexia, TX
One of the grounds might not be very good. You could either jumper the two ground connections together with wire on the back of the cluster, or jumper them and run a single wire to a new ground. You could run two separate wires but for as small of a draw as that tach is, it won't need that much.
Thread
Thread Starter
Forum
Replies
Last Post
82fordowner
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
5
Apr 8, 2013 02:54 PM
jmkelly
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
2
Jun 9, 2007 07:56 AM
DT 466Man
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
7
Feb 23, 2005 08:53 PM
MagBayBrian
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
12
Nov 25, 2002 09:32 PM