Compression Ignition Addict
Join Date: Oct 2011
Location: Tehachapi, CA
Thanked 87 Times in 85 Posts
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First suggestion: If you plan to keep or work on the truck, get an Electrical and Vacuum Troubleshooting Manual (EVTM) from Helm Inc (about $22), best money you'll ever spend.
The tachometer gets it's signal directly from the Powertrain Control Module (PCM). The PCM is low on the driver's side firewall inside the engine compartment (NOT the one below the driver's side hood hinge ... that's the Injector Driver Module or IDM). It will be a White wire with a Pink trace (circuit 648) from PCM connector (C1027) pin 50 (for a 49-state truck) or pin 19 (for a California truck). It will go from the PCM connector to the big firewall feedthrough connector (C202) pin 25. From C202, it will go to the instrument cluster connector (C250) pin 9. The ground is from C250 pin 3 (circuit 57, Black wire ... there is another ground on pin 7 and they are spliced together). Cheers!
1997 F250 SC 4x4, E4OD, 4.10 LS, Basically Stock, Relocated Block Heater Plug, External Trans Filter, Tru-Cool Max, I/C Mounted but not Plumbed
SOLD - 1994 F350 CC DRW 2WD PSD, 5 Speed, 4.10 LS, SBC Con-O, Baldwin Filter, Tymar HPX Hose, DPPI DP, Bilsteins, $12 AIC, Coolant Filter, Explorer Overhead Console, A-Pillar w/ISSPRO Black Ice, EV Boost, and EV Pyro, Modified Pedestal, Gutted EBPV.