bench tests of rectifier charging system and tach

[eaganboater1]

my 1979 johnson 100hp has a dead instrument cluster. last year i had the engine rebuilt and they replaced the rectifier. my tach has never worked. i havea wiring diagram from a manual, but i dont understand the tach/charge ciruit.

i was told by a local boat part supplier that amp gauges are very old school, that the way to verify your charg system health is with a voltmeter - is that correct?

Is there a way I can either staticlly test the rectifier with a simple fluke type gauge, or can i check current output in system while at idle somewhere?

related, from i can tell, is the tach doesnt work (i'm pretty sure recifier is good, boat hasnt died all summer), but is there a way to bench test this to see if its the gauge or in the wiring harness? Where should the terminals connect to on the eninge for the tach to function properly?

finally, the voltmeter is new, its a faria, but i connected it up wrong. can i go directly to engine off a fused circuit, or should i put it on a switched hot lead from ignitition - if so, how do i test with voltmeter what a good lead wouold be?

 

[greens1098]

Re: bench tests of rectifier charging system and tach

When you say dead cluster. Is everything dead? Or is it just the voltmeter and tach? If those two are dead and you have tried difference gauges and you are positive that the wiring is correct then Id have to venture off in saying that the RPM side of the Rectifier is bad. Now I cant be certain thats where your tach pulse comes off but what I would do is get your wriing schematic and i think the gray wire is your pulse. Run that two a tach and see how it goes. Let me know.

 

[eaganboater1]

Re: bench tests of rectifier charging system and tach

thanks for the reply. here's the challenge. i have the dash out. there are prorobly a dozen leads that i have disconnectedat the gauges, many i know to be hot. full disclosure, i got the boat with a rats nest of wiring. i bought a cmer manual, and documented what was there, then stripped just about everything out (everything for the dash) leaving the start circuit and tilt circuit alone (they worked.)
many of the wires out of the harness or into the switch are foamed in place under the top edge of the hull. so i couldnt completely start fresh. at the time there was some uncertainity on the wires from the various engine or switch leads terminated near the dash, as the previous owner had cut many of them.

that being said, i pulled about 400 ft of wire and routed everything to one of two new fuse blocks under the dash. one dash is set aside for auxillery power accessories.

i dont have a manaul tach, and im not so comfortable firing the engine with so many loose leads, and i would rather not have to buy a tach if i dont need it. is there some way to test the tach's circuitry to see if its good?