So after doing some research I have found that a gas tachometer can work as long as you have the appropriate alternator with the 'w' terminal for the output signal. However I have also been told that the tach will read very high rpm if a gas tach is being used on a diesel motor unless you modify / recalibrate the tach. Anyone been through this? Going to need to figure out how to hook it up on my 83 audi 4000 diesel (with coupe GT tach cluster). Help appreciated!
long story short ... go to the facts and look up "tachs"
Your diesel rev signal will/can come from the "W" output of your alternator but your gas tach won't read it because it's the wrong type of signal. So you need to modify the gas tach appropriatly (some condensors & resistors to change).
I'm also involved in this at the moment. Have an 82 tach from a gas rabbit to put into my 81 diesel pickup. Following 4crawler process, I've switched the tach into my original cluster box. I have a 'W' alternator waiting to be installed. I am confused where to go next. I've read all the postings in this and other forums regarding making 'hard' circuit board mods for the tach, but the tach board cannot be removed without destroying it.
My conundrum at this time is how to get the tach operating. How it gets its 12v power? Where does the 'W' wire connect to the tach? There are no terminal connecting points on the back of the tach. Want to get these points clear before removing my spare cluster from the truck. I've emailed 4crawler and am hoping that with his help to have it installed soon.
long story short ... go to the facts and look up "tachs"
Your diesel rev signal will/can come from the "W" output of your alternator but your gas tach won't read it because it's the wrong type of signal. So you need to modify the gas tach appropriatly (some condensors & resistors to change).
There is a post here somewhere. That shows the quickest way to use a gas tach in a diesel MK1. I think he's jimbote. Mounted a Ford crank sensor near the crank pulley, welded 2 nuts(180 cross from eachother) wired sensor to tach done! Haven't done it yet but will in my MTDI Caddy.
all i did was tap into the wire behind the fuse pannel for the... upshift light i believe? i forget. i looked it up in the bentley.
with one of these things: (image couteousy of google)
took my VDO gauge and there's three switches on the back. moved them till they gave me a close to acurate reading. (you can closer calibrate it by a hole on the side of the gauge with a percision screw driver)
and viola! that's if you like having 2 1/16 gauges.
[oh and i also have a alt from a mk3 golf in the car due to the abf set up. i don't know if that makes a difference. i know that one had the w terminal.]
OH I REMEMBER NOW. i did have to go to the junk yard and rumage through the mk3's and cut a connector for the altenator to make it work cause the connecter i had wouldn't. and i needed one with two wires i think. not one... yeah. i butt connected the new connecter to the old alternator wire. the blue i think went to the exciter and the yellow went to the w-terminal. i don't think those colors are correct but you get the idea.
I'm also converting a gas tach to the diesel "w" terminal. I am electing to go with a Dakoda Digitial signal converter which converts the "w" signal to the gas tach signal. I bought one on ebay $62 with free shipping, and am hoping it will do what it says. 4cralwer spent more than that on making an optical setup.
Although if this converter doesn't work, then I have wasted my money anyway, and at least his system works to an extent.
I have taken my Bentley and searched the wiring diagrams and looked at the back of my gas tach (and circuitry since I have the whole gauge cluster) and where the wire goes to the plug in. I will bring the wire from the converter to the appropriate terminal on the plug or tap into the current wire going into the plug and think this will be good. I haven't done it yet, but this is the plan. I have looked at the wiring diagrams, and looked at the wiring of my current plug (1980 caddy with speedo only cluster) and have traced the wires and where they go and what they do. I plan to match wires from the plug to the approriat terminals. I am blessed to have a 12 prong plug and a 14 prong plug. I will need to match as I get ready to install.
It seems that if you can find the wire from the tach and/or if you have the whole cluster assembly you can trace the tach line to the appropriate terminal on the plug, either through tracing or by looking at the wiring diagram and finding the tach terminal on the plug, then tracing it back to the tach terminal.
This is all theory with some experimentation at this point, but thought it would share it so that others can interact and confirm or correct that this is a good route to go.
I am hoping the converter will be the most painfree way of matching signals and getting an accurate reading. I posted a question about the converter and got some feedback, but I dont' know I have found anyone who has used it and responded. So, it might be prudent to wait until I have actually installed it, or someone else who has installed the coverter can share his/her experience. . Anyone actually used one and how does it work?
Hope this helps some.