Waferboy

Fox Mustang Tachometer Repair and Dash Bulb Maintenance

Symptom: With engine running, Tachometer stayed at about 3000 rpm from idle to ~2000rpm where the needle would them move up again. When engine was off, Tachometer would return to 0 rpm.

Problem: Removal of the Tachometer allowing viewing of the back electronics reveal soldered joints which were broken

Resolution: Reheating and applying new solder to the broken joints

Repair Process: Remove the instrument cluster from the dashboard and pull the Tachometer out. MustangMonthly Magazine has this detailed out quite well on their website. In this article it turns out MustangMonthly was replacing a Tachometer which had a problem very similar to what I have described above. So save yourself the money and take a look at the Tachometer before going and buying another one. The article is located here:

Once you have the Tachometer pulled look closely at the solder joints. Look for breaks or cracks in the solder. I couldn’t get my camera pull a good picture of it but below you can see the brown region of the Tachometer electronics. In my case this brown area had a few cracked/broken solder joints.


To repair the broken solder joint, use a hot, clean soldering iron to reheat the joint and apply a small amount of new solder. Do not heat the joint for a period longer than it takes to melt in the new solder completely on the joint. Heating the joint for too long can ruin the traces from the joint and/or ruin the component which it is soldered too. I would recommend that while you are here to heat and reflow/add to the solder of every joint on the board.

Also since you have the instrument cluster out, it's a good opportunity to perform some maintenance on the cluster bulbs. My '93 had a few bulbs that worked for some of the seasons with Winters making the most bulbs not work. Come Springtime the lights would work again. This hinted to me that there was a poor connection that temperature/humidity was affecting.

Performing maintenance on these bulbs is simple enough. They come out with a 1/4 turn of the bulb and an easy pull. With the bulb out, use a DVM to test the resistance across the bulb. If it's open it's burned out, if it's < a few Ohms the bulb is still good. Turned out that all my bulbs were good. If the bulb is good, clean the connections with some 400 or more grit sandpaper or a pencil eraser and reinstall the bulb. Note that cleaning should be done lightly, and should only be enough to put a shine back to connections. It shouldn't take more than a couple rubs... rub things too much and you may go right through the contact. Once cleaned up, any shady connection should be good once again.


After resoldering the joint(s) and cleaning the bulb connections, look closely at the joint(s)/connections and verify the soldered connection looks good lacking broken connections or bad traces. Verify all the bulbs are installed correctly.

With all the verifications done, reinstall the Tachometer into the cluster assembly, hook things back up and check it all out.

Hope this helps some folks out!

lxman1

Nice write-up. Thanks