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I'm wanting to connect a VDO tach. the 3500 doesn't have a coil +/- so I assume I need to connect to alternator but where?
besides the charge post there's 2 wires on a 4 pin plug out of alt.
thanks
Since you only have a 1 wire alternator and no/multiple coils, and no distributer, the Crankshaft/Camshaft position sensors provide engine speed to the ECU. You will need to tap the ECM connection to get the signal to the Tach. I don't know which wire will provide the signal but there may also be an issue since the ECM may not be a 12V signal. I do know the only way to get the info in your engine is from the ECM. There is a possibility the Tach you purchased is not compatible with your truck because the Tach schematic is for older engine configurations, Coil schematic or 4 wire Alternator, which haven't been used after GM went to the ECM, fuel injection, and crank/cam sensors. (the coil or "electronic control box (mopar) is pre-ECM. Maybe some else on the forum has the ECM pin for a Tach trigger, sorry but I got rid of my Helm 2000 Silverado manuals a couple years ago.
They mention a "red harness." I think they may talking about the red/blue connectors at the ECU. You may have that, and not the blue/green ECU.
read the thread seams kindof complicated.
I can set the # of cylinders on tach got lost when they wanted to boost the tach or maybe that is just for autometer tachs.thanks though.
Originally Posted by OTCyber Guy
Since you only have a 1 wire alternator and no/multiple coils, and no distributer, the Crankshaft/Camshaft position sensors provide engine speed to the ECU. You will need to tap the ECM connection to get the signal to the Tach. I don't know which wire will provide the signal but there may also be an issue since the ECM may not be a 12V signal. I do know the only way to get the info in your engine is from the ECM. There is a possibility the Tach you purchased is not compatible with your truck because the Tach schematic is for older engine configurations, Coil schematic or 4 wire Alternator, which haven't been used after GM went to the ECM, fuel injection, and crank/cam sensors. (the coil or "electronic control box (mopar) is pre-ECM. Maybe some else on the forum has the ECM pin for a Tach trigger, sorry but I got rid of my Helm 2000 Silverado manuals a couple years ago.
yes it's a old tach I used it on a none GM that car had a distributor an only one coil, which is where I got signal from.
my alternator on the 04 express has 2 wires on a 4 wire plug solid white an solid orange. this in addition to the larger charge post that goe's to battery.
what is the 2 wired piece to left of alt. ontop of firewall? could this be an external regulator for the alt.?
edit:if I had a newer Tach. designed for the coil to plug type vehicle would I still have to cut into the main wire harness? image of alt. thanks for tach advice
01-29-2023, 12:55 PM
connecting a Tachometer 04 3500
