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Converting '69 Chevelle Idiot Lights to Factory Tach
(Special thanks to David Brewer for correcting some mistakes)
Click here for a Printer Friendly Version

Well, they said it couldn’t be done. Just goes to show, "they" aren’t always right! I recently added a factory tach to my 69 SS in place of the useless idiot light cluster. Most of the people I spoke to prior to doing this, said it was not possible to do this conversion, without first installing the correct wiring harness for the gauge cluster. (To the tune of about $350!) This is incorrect!!

Before beginning this project, I checked all the sites, and picked as many brains as I could and was hard pressed to find any kind of in-depth technical info on doing this conversion. I was also unable to find a wiring diagram showing the wiring for an original tach cluster, making this project a little tougher! Well, with all of this behind me, I’m sure that there are others of you out there that are contemplating this, so I decided to write this up and add some good pictures to help you along. I hope someone finds this useful!!! Before beginning, you’ll want to make sure all the gauges in your cluster work. I sent mine to Clock Doc (1-800-256-5362), where they bench tested all gauges, and rebuilt my battery gauge and rebuilt my tach, which was cooked. (Hint: This wasn’t cheap, but did come with a guarantee!) PHOTO #1

The tools/supplies needed to do this job include:

  • - temp. sending unit for gauges
    - oil press. sending unit for gauges
    - wire cutters, wire strippers
  • - wire crimpers
  • - ¼" drive socket wrench
  • - ¼" socket
  • - 3 or 4-inch extension
  • - crimp on insulated female end connectors
  • - one small crimp on
  • - lug end. (A round-end, for your tach connection at the coil.)
  • - brown 18 gauge wire for the coil to tach wire
  • - 3M crimp on wire splice
  • - #57 replacement bulbs. (You’ll want to check and replace any burned out bulbs  while you have this pulled apart.)

You will also need to replace your oil and temperature sending units with units for gauges. These should fit the original connectors for the original sending units. However, some knucklehead cut the temp connector out of my harness and re-wrapped the harness, after installing after-market gauges, so I had to cut into the wiring harness to find the original wire and then attach the correct plug. I got the plug end from a company called True Connections. (e-mail them at trueconnect@earthlink.net ). I purchased my sending units from a local Pep Boys store for about half of what Year One was selling them for in their catalog.

Okay, lets get started. I’m assuming that you’ve already installed the correct sending units, and removed the dash face, (the cluster is fastened to the back of the dash face by (7)- ¼" screws). If you haven’t already done so, you may want to remove your steering wheel, and drop the steering column for easier access PHOTO #2. Once the dash face is removed, take all the bulb-housings out of the fuel gauge cluster, and disconnect the fuel gauge connection. Now unbolt the fuel gauge cluster from the housing. This is held in place by 4 more ¼" screws. (Note, there’s a ground wire that attaches to the bolt on the very inside (Where your round Chevelle emblem or clock sits, in the center of the cluster) don’t forget this is here when putting the tach cluster back in.

Here’s where the fun begins!! Cut off the bulb-ends (Except for the battery light : brown & pink wires which must stay connected to complete the charging circuit. (The alternator needs resistance from the bulb. There is a resistance wire (#24 brown with white stripe) under the dash that runs in parallel with the brown wire that goes to the battery indicator bulb. This wire is there just in case the battery indicator bulb burns out, the alternator will keep working properly. The electricity that energizes the alternator comes from the idiot light (thru the brown wire), and the alternator needs to see some resistance in this line. That resistance is the bulb. If you take that resistance (the bulb) out, the alternator will not function properly. You cannot by-pass the light! You have to
run two new wires for the ammeter (battery gauge). One wire goes to the junction block on the radiator support behind the battery, and the other wire runs to the battery terminal on the horn relay. Both of these wires should be #16 with a #20 fusible link installed on both. The fusible links are very important, as without them the gauge is unprotected, and could be shorted out. Cut wires for, the oil light (blue and pink) and the temp light (green and pink). DO NOT cut the Fuel gauge wires off of the black plastic
connector as this will be the same on the tach cluster and will just plug in! You’ll notice that all of these lights have a pink wire in common.

This obviously is your 12v-power feed from the fuse panel, powered by the "gauge" fuse. (We’re going to tap into one of these pink wires to use as our 12v power for the tach later.) Here’s where we crimp on those female end connectors. Crimp one end on each of the wires you just cut the bulbs off. (Don’t worry yet about where each is connected.) Next, make up your harness
for the tach. I crimped on the round lug to the end of a 3-½ foot piece of the brown wire. Connect this to the negative side of the coil. Run it into the interior through the cowl and route it where it’s out of the way. Figure out what the length you need will be and crimp on a female end connector after cutting the wire to desired length. Next, make up your tach power wire. (I used a piece of different color wire just to keep it easy to identify, but the brown- colored wire will do) Crimp on a female end , then attach it to the plug on the tach. Run the other end to one of the pink wires. (I used the pink wire for the temp gauge.) Use the 3M connector to
splice into the power wire, and create a power lead for the tach. (This could be done a few other ways, but I felt this was the simplest and cleanest way to do it. Plus I wanted to keep all the gauges on the same circuit.) Right about now, you’re probably getting a little thirsty so grab a beer or coffee, and look over what you’ve done so far and think about what’s next!!  This is one job that goes much easier when you work slowly and think ahead!

Now we’re ready to start making our connections PHOTO #3. DIAGRAM #1. The brown wire will go to the Battery gauge negative terminal, pink wire to the 12v positive side. Blue wire (from the sending unit) to the Oil gauge negative, pink to 12v positive.  Green wire (from sending unit) to Temp gauge negative, pink to 12v positive. Attach the brown wire to the Tach negative side, and the positive (whichever wire you spliced into the pink wire with the 3M splitter) to 12v positive tach connection. Now plug in the black fuel gauge connection.

Now it’s time to fire up the gauges!! Put the cluster into the housing and temporarily, fasten it in with 2 bolts, one on each side PHOTO #4. Check the fuses in the fuse box and make sure they are all intact and the correct amp ratings. Now turn the ignition key to the "Accessory " position. Your gas gauge should move and possibly the others as well. Most likely the oil & temp will go to the bottom. The battery will probably not move until the car is running and some electrical things are turned on. (Headlights etc…).

Fire up the car and watch that tach jump to life! If everything works shut it down. Check all the dash bulbs and push them back into the cluster. (Double and triple check these they’re a real pain to try to push back in once the cluster is mounted in its place!!) Bolt your cluster back in and put the dash back together. Don’t forget the ground wire that goes from the center pod, to the tach cluster in the rear PHOTO #5. This is the ground for your dash lights. That’s all there is to it! You’re done! PHOTO #6.

I had no problems when doing my conversion and everything fired right up. If you do experience any problems, double check all fuses, all grounds and all crimped on connectors, in that order! If anyone has any questions or comments, feel free to e-mail at Noneck. I am by no means an expert and my weak point on cars is electronics. I will however, do my best to help you out if I can!

Copyright © 1998 NoNeck's

 

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