What wire to use for tach install?
Senior Member
Joined: Apr 2006
Posts: 225
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From: Indiana
Sorry, I don't have the answer to your question, but I might be able to point you in the right direction. If you bought a standard, plain-jane, tach, you may need to return it and do some research before you buy the next one. Most generic tachs are designed to hook to +battery, ground, usually a seperate +12V line attached to your headlight switch (for night time illumination) and one more wire to be connected to the negative side of your coil.
That's the catch, your truck has coil packs or COPs, depending on if it's a 4.6 or 5.4, no single coil, so no single negative side of the coil.
That said, I believe the tach output for these trucks (assuming a tach was in the dash) comes directly from the ECM. What wire it is I have no clue, but I am sure someone on here could point you in the right direction. What the electrical signal on this wire looks like I have no clue. It might be similar to a coil's low side output, but I doubt it. Either way, I believe that is what you need to track down. On possibility that could be an issue... Since obviously your truck did not come with a factory tach, it is possible the tach ECM wire is not present in any wiring harness. This might have been a way Ford saved a few cents... Copper cost money, and when you produce a few hundred thousand vehicles every penny counts. I'm not saying that is the case, but it is a possibility to consider. Even if the wire is not there, you could see about getting a junkyard wiring harness, extract a pin and some wire (easier said than done without an extraction tool), and insert the pin on the proper mating pin of your factory ECM.
For your sake, I hope I am wrong and this is simpler than I imagine, but I doubt it based on the lack of responses you have seen. Someone else was asking about this topic a few weeks ago, but the name has left me. You might do a search and see if anything was ever found out.
Mike
That's the catch, your truck has coil packs or COPs, depending on if it's a 4.6 or 5.4, no single coil, so no single negative side of the coil.
That said, I believe the tach output for these trucks (assuming a tach was in the dash) comes directly from the ECM. What wire it is I have no clue, but I am sure someone on here could point you in the right direction. What the electrical signal on this wire looks like I have no clue. It might be similar to a coil's low side output, but I doubt it. Either way, I believe that is what you need to track down. On possibility that could be an issue... Since obviously your truck did not come with a factory tach, it is possible the tach ECM wire is not present in any wiring harness. This might have been a way Ford saved a few cents... Copper cost money, and when you produce a few hundred thousand vehicles every penny counts. I'm not saying that is the case, but it is a possibility to consider. Even if the wire is not there, you could see about getting a junkyard wiring harness, extract a pin and some wire (easier said than done without an extraction tool), and insert the pin on the proper mating pin of your factory ECM.
For your sake, I hope I am wrong and this is simpler than I imagine, but I doubt it based on the lack of responses you have seen. Someone else was asking about this topic a few weeks ago, but the name has left me. You might do a search and see if anything was ever found out.
Mike
Technical Article Contributor
Joined: Dec 1997
Posts: 9,417
Likes: 11
From: Windsor,Ontario,Canada
Find the tach lead at the instrument cluster connector and tap into that. It is white with pink stripe. It should be on the White connector with 14 pins. (The Connector actually has 16 slots but only 14 pins.) It is the longest of the connectors.
JMC
JMC
Member
Joined: Jul 2006
Posts: 91
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From: Sother California