Pete is correct, the gauges and the speedo / tach get power from 2 completely different circuits. They do, however, share a common ground, if I remember correctly. Could just be a bad connection at the cluster connectors..... went thru that a few weeks ago myself.... had lcuster out to replace the mechanical IVR with a solid state one (a different design than the one in the tech articles, and it works great.... none of the problems that seem to be associated with the one in the tech articles). After putting the cluster back in, and putting the dash together, went for a ride, and after about 10 min, speedo quit working. Out came the cluster again.... I sprayed contact cleaner in the connector at the top, and lightly sanding the printed circuit connector at the bottom, followed by contact cleaner, and it has been fine for 1000 miles.
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Jeff Korn
88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 21 psi, forced air intercooler, water injection, bypass valve, Ranger roller cam, subframes, etc., etc.. // 86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP nitrous, ignition, gears, suspension, etc., etc.... // 91 Escort: Bone stock winter car // 02 Taurus Vulcan(wifes car)
Jeff Korn
88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
11 Crown Vic Interceptor
14 Toyota Camry (wifes car)
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized