Interesting Alternator Issue
 

I have a 94 Suburban 6.5T, I just bought it this weekend! Today the tach starting "dancing", it was quite odd and only did it at idle.
Nest the battery light came on and the volts dropped to 12, it was not charging at all.

I first cleaned all the battery cable connections and terminals, no help.
Next I tested the output of the alternator, no output.

I found it odd that a loss of charging would affect the tachometer, is this normal?


On a side note the truck runs great, like most have said it is not a powerhouse but it gets the job done for me.

Future mods include the relocated and heat sinked PMD, Walking J turbo and KOJO chip and straight piped 4" exhaust with 3" DP.

Your tac. is run off the alt. You probably lost the alt.

Yeah, I replaced the alternator and all is well, good to know about the tach feed in the alternator.

Dancing Tach
 

We had a similar issue. We found that the engine was grounded through one battery but not the other, apparently the ground straps on the engine had rotted. For a few minor bucks we installed a new heavy duty "strap" lawn mower battery cable from the engine to the fire wall. Electrical settled down and lights worked wonderfully. Use a meter and verify yours...

Paul

these trucks are infamous for gauge porblems too...