no tachometer

[rrr1021]

hi 1989 int 1700 7.3 5spd tach doesnt work turn key on and needle moves all the way over then running eng no movement where is the signal coming from , inj pump or a sending unit elsewhere please aSSIST THANKS

[DKinWA]

I may be way off base, but I had a gauge do the same thing and it was a bad ground. I don't remember which gauge, but it did the exact same thing.

[eclmech]

I believe in some older 7.3's the tach output is from the alternator. Just a problem that I've seen.

Keith

[synner]

We seem to be having the same problem from time to time with our 2001 4700 with the 7.3.

Sometimes the gauges work, sometimes they don't. Usually shutting off and restarting the truck works.

At the same time the aux. circuit switches won't power up either. Same deal usually have to shut down and restart a couple of times. Bit of a pain when trying to get the dump body to work.

We tried replacing the ign. switch thinking it had a bad ground/connection internally but the problem still exists.

Is there a main ground lug/terminal post on these vehicles up behind the dash?