How do I test a tach
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Senior User
Joined: Mar 2014
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From: AZ
How do I test a tach
OK, 1983 Flareside F100 with 302. It has factory tach, but has stopped working. I have been rebuilding this truck and put in a new distributor and coil. When the truck is running I am getting 7 volts on the two right side points of the back of the tach. I grabbed another tach from the junk yard and no success. How do I test the tach itself to see if that is not the problem? Then, do I just test continuity on the green wire from the coil to tach. Am I missing a ground somewhere? Thanks
Lead Driver
Joined: Jul 2009
Posts: 6,477
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From: Sheffield, AL
On the back of the factory tachometer are 4 terminals. You might remove the tachometer for testing purposes, so the test wires will be shorter.
"B" is battery [12 volts]
"C" is coil [negative side]
"G" is ground
"8" is a 2nd ground, which is required for correct calibration of tachometer when for a V8
Six cylinder trucks use the same tachometer, but do not utilize the 2nd ground. It normally is all taken care of within the wiring harness.
When replacing the distributor and coil, you may have left a wire disconnected. Look for the green wire which connects to the negative side of the coil.
"B" is battery [12 volts]
"C" is coil [negative side]
"G" is ground
"8" is a 2nd ground, which is required for correct calibration of tachometer when for a V8
Six cylinder trucks use the same tachometer, but do not utilize the 2nd ground. It normally is all taken care of within the wiring harness.
When replacing the distributor and coil, you may have left a wire disconnected. Look for the green wire which connects to the negative side of the coil.
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Senior User
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From: AZ
OK, the tach tests fine. I put my voltage tester to the "B" while fully installed and get nothing. I assume it is just not getting any juice. Any ideas on how to trace this? Which wire from the plug in on the back of the cluster. Also. all other gauges work fine.
Cargo Master
Joined: Mar 2008
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From: Washington
You could just add a wire, here is a photo
https://www.ford-trucks.com/forums/9...ml#post8307310
Jim
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Senior User
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From: AZ
You could just add a wire, here is a photo
https://www.ford-trucks.com/forums/9...ml#post8307310
Jim
https://www.ford-trucks.com/forums/9...ml#post8307310
Jim
Cargo Master
Joined: Mar 2008
Posts: 2,564
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From: Washington
Is it reading anything?? or just a dead needle??
Jim
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From: AZ
It is reading nothing. I have hard wired it like the forum you sent me. I am just not sure where to attach the 8. Is it somewhere on the distributor or the positive of coil?
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Cargo Master
Joined: Mar 2008
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From: Washington
Just connect 8 to G
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