Factory Tach wiring?? - Dodge Diesel

RollinCoalSmoke · 10-26-2009, 06:37 PM

I have a factory tach that has not worked since I bought the truck. Today while saying many many bad words pulling out the headlight switch that burned up this morning I found the factory tach had the wire just hanging about 6'' below the tach. Anybody know what goes to what? There are 4-yellow wires----1 red wire-----1 grey wire----1 black wire. Any ideas?? The headlight switch is a bugger to get out when the time comes guys. Mine has worse problems tho--the plug is melted way gone.

Crossy's son · 10-26-2009, 06:48 PM

your tach wire does not have a plug on the end ?? just wires ?

it should have a plug that hooks up to the male part of the plug coming out of the harness, next to hood latch tied around the main harnes.

BC847 · 10-26-2009, 07:15 PM

The OEM factory tachometer plug offers the following:

- 18ga Black = +12vdc for gage lights
- 20ga Orange = 12vdc Common
- 18ga Red = Switched +12vdc
- 20ga Grey w/light blue tracer = Tachometer Signal From PCM

The following schematics show where the above comes from. The images are high resolution so you can zoom in to make them out better.

OEM Tachometer ~ +12vdc f/Lights / -12vdc Common

PCM Signal To Tachometer

Switched +12vdc To Tachometer

Hope this helps.

10-26-2009, 06:48 PM	#2
Crossy's son Registered User Join Date: Jan 2008 Location: South Plainfield, New Jersey Posts: 7,467 My Photo Gallery My Classified Ads	your tach wire does not have a plug on the end ?? just wires ? it should have a plug that hooks up to the male part of the plug coming out of the harness, next to hood latch tied around the main harnes. __________________ 91.5 W250 4x4 5 speed LE Red/Grey, 270k miles, 3.54's w/ Power-Lok, 4" Exhaust, BHAF, DennyT Pin, 3200 Spring, Piston LP, Power screw maxed, HX35/12cm, DAP 5x14 Injectors, Valair 13" 550hp K/C clutch, 4" Skyjacker soft-ride lift, 315/75R16 Mickey Thompson Baja ATZ tires, 16-17 MPG 89 D150 3.9L TBI/A999 Auto, beater while ^^^ gets restored Attending LTI for Diesel Truck Technology, graduate December 2013

10-26-2009, 07:15 PM	#3
BC847 Administrator Join Date: Jan 2005 Location: Buies Creek, NC Posts: 4,267 My Photo Gallery My Classified Ads	The OEM factory tachometer plug offers the following: - 18ga Black = +12vdc for gage lights - 20ga Orange = 12vdc Common - 18ga Red = Switched +12vdc - 20ga Grey w/light blue tracer = Tachometer Signal From PCM The following schematics show where the above comes from. The images are high resolution so you can zoom in to make them out better. OEM Tachometer ~ +12vdc f/Lights / -12vdc Common PCM Signal To Tachometer Switched +12vdc To Tachometer Hope this helps. __________________ David Original owner of a 1993 W250 CC.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode