I installed a 86' 2nd Gen altenator with the double pulley on my 12a 82' GSL. Work'd fine for 2 days and when I was driving it home from the swap meet the tach died(both of them) no other issues have happened. I checked the fuse box and found nothing blown. The car runs fine so I have rule the ignitor out. Could it be the trailing ignition coil? I have had a ignitor fail on me (trailing) and had the Tach fail and the car ran lousy. Not the same problem. Did I hose my electrical when I did the Altenator swap, I spoke to other guy's that had the early 2nd gen altenators and they had no issues. the late model 2nd gen units(88'-92') did cause battery drain until a relay was installed(somewhere) for other guys. Battery drain isn't a issue with my problem.
Help!

 

Do you have 2 tachometers? I have to say its a wiring problem with the tach. Nothing to do with the alternator swap. If the car is running fine, then check the wiring for the tach. Make sure all the connections are good. The tach will still work even if a coil is no good. The only time when a tach won't work is if the wiring is bad or an ignitor is gone.

 

I have a after market tach on the dash, it's wired independently of the stock tach. I checked the wire, fuse and ground. Nuthin out of the ordinary. Ii faile to mention that just before they failed, they fluxed up and down and went nutz before they died.....sorry for leaving out the important stuff.

 

Something doesn't sound right. It sounds like the ignitors are going out, but you say the car runs fine. I would say that its the tach itself, but it happened to both tachs, so I don't know.

 

Easiest way to check, just swap the ignitors around and see if the car still runs. If it does, then it isn't the ignitors.

 

I feel pretty stupid. I swapped the ignitor leads and both the tachs came back. I thought that ignitors either were on or off(bad). Didn't dawn on me that it could be just fickle. I have a spare ignitor and will swap it out. I hate that because I have to remove the Altenator that I just installed! Thanks for the input and ideas.
Best regards

 

why take of the alt?

 

Easier to get at the ignitor that is installed there between the dizzy and alt. Pain in the butt otherwise. I've done it with a low profile 90deg. screwdriver but if you don't have one, next best thing to do is remove the alt.

 

is putting a second gen alt on hard or anything, os is it pretty easy

 

Pretty easy, but when I put the dual pulley on, I fubbar'd a fin when I used a screwdriver to keep the rotor from turning to tighten the pulley nut. Make sure you use a 86'-87' 70amp alt not the 80 or 90amp alts without consulting someone who has. Also make sure you get the spacer that the alt came with, you'll need it as it is smaller than the 1st Gen spacer. I'm pulling 13.5 volts with all of my lights and the fan on, including blinkers. Windows come up faster too.

 

R&R'd the ignitor last night and all is well with the tach's.

Weird how the car ran just fine with a bad ignitor but the tach failed.....must be a full moon somewhere.

 

The tach runs off the trailing ignition. If the leading ignitor went out you would notice a huge difference, the car would barely run, but the tach would work.

 

Right, that's why I replaced the trailing ignitor(the one facing the altenator)