Diesel rally pac problem

[Oldstech]

1981 Cutlass Supreme with Olds 350 diesel

I install my Diesel Rally pac guages today. My Voltage guage nor my tac is working. The tach is acting like it wants to work. During cranking it jumps to like 500 rpms but after start up it goes to 0. And zero outs when I turn the key on. The Voltage guage doesn't even move. I read this problem in another thread of this same problem. But he didn't post how he fixed it. And Im not sure even how the tach works on a Diesel. But it is acting like it should? Im used the gmail wiring instrutions. Anyone got any advice. Now the instructions said to cap two wires. One being a light wire and the other a ground. I was curious if the ground might be for the voltage. But not sure.

BTW, no I didn't install a white wire for the tach. I didn't except the tach to work. But it is acting like it should or is trying. And being diesel I wasn't sure

 

[KrisW]

Believe it or not, your diesel is supposed to get the tach signal from the alternator. If you look at your alternator, there should be a TACH terminal on the back of it and a wire going there and bolted on with a small nut. If you don't have that, then you have to get another alternator. When you get one at the auto parts store they will ask you if you have a tachometer or not.

Of course, that doesn't guarantee that it will work either!! It was a crap design for a tach drive, but it's better than nothing.

As for the voltmeter fluctuating, I have had this problem as well. My rally pac was doing all of the same crazy stuff when I first got the car. After taking it out and putting it in a lot, I discovered that the plugs in the back were not making a good contact with the PC board on the back of the gauge cluster. I had that stupid dash apart so much, you wouldn't beleive it!!

I got all the gauges working but it took lots of fiddling with every wire connection back there to do it.

Incidentally, did you just pull a rally pac from another car and try to make it work in yours? If so, you are at the beginning of your headaches. The diesel cars have a different wiring order going to the gauge cluster because of the glow plug lights and such. Be careful.