The other day tach stayed at zero. I gave it some throttle, and it jumped and worked. A couple of days later, dead again, but this time it stayed dead. I checked all wires in back of tach, and all connected OK including the bullet connector. Someone said there was something on the bike that sends impulses to tach from somewhere around the engine, but I don't know what it is or where it is. Can someone help please? Thanks.
The first thing to try, if possible, is to check the two screws into the white back of the instrument cluster that anchor the two electric wires for the tach. They take a #2 Phillips (or Jap equivalent) screwdriver and might be loose on a '91.
If your tach is still dead: I think the tach has simply one ground/earth wire (usually green) and one signal wire (with some yellow, I think). If you can, put a voltmeter across those two wires. That is, connect one meter lead to the ground wire (green), and one to the signal wire (yellow). Start the engine, and watch for a voltage change.
1. If a voltage change is seen, roll on the throttle, and look for even more voltage change. If seen again,
tach is bad,
or those wire connections have rust on them. (I'd
double check for rust where the two wires bolt onto the back of the tach.)
2. If no voltage change is seen, you may have to pull your gas tank and go a looking at that pulse generator at the top rear of the engine. (But I've never seen one of those fail.)
Bottom line: I'd
look for loose wiring or a rusty connection at the back of the tach. (That back of the tach can get wet. You have a rubber cover over it to shelter it, right? You get a lot of rain there in Plantation? Is that Florida?
By the way, the instrument cluster is not that hard to remove and disassemble, IMO, if it comes to that.)
(Reference: Any ST1100 SERVICE MANUAL WIRING DIAGRAM.)