Okay so I KNOW this is NOT a trans am site, but my car has an olds engine!

Anyway I just acquired a 1979 Silver anniversary car with 93k miles drove her home 400 miles with no issues other than the tach is pegged whether the car is running or not.
So I got the crappy (haynes) wiring diagram and found the wire to the coil from the tach is supposed to go through the firewall and up to the tach and is a pink wire, well there is NO wire at all on the tach wire side of the distributor but I found a pink wire inside the harness, that I cut just to test out what happened KNOWING I could just splice it back if I need to and the fact that it is SUPPOSED to be the tach wire anyway, when I went to start the car all is dead except headlights, no interior lights nothing on dash etc..........so I used my test lead and hooked the pink wire back together and the dash lights etc worked and the car started right up and ran fine, so my next test is what happens when I disconnect the jumper on the pink wire while the car is running, well the idle drops a bit and i go look at the tach and it is down to 5000 rpm instead of being pegged at 6 grand, so i open the door to get a better look at the tach and the car shuts off

tested that situation again and got the same result after hooking jumper back up to start car, tach goes pegged again and car starts then unhook jumper, tach drops to 5k, open door car shuts off again
So of course some SUPER GENIUS had to install some alarm system along the way and there is some idiot super stereo system in it as well, do you guys have ANY idea of where I can start with this thing ???????
I need some expert electrical help here gentlemen!

Thanks

 

is it an after market tach with a switch on it possibly?, i bought a cheap one to have something to monitor my rpm's and it has a 4-6-8 switch on it, Hope you get your problem fixed

 

When there are factory service books with complete and accurate wiring charts available, why are you messing with a Haynes manual?

If I had to guess I'd say it's related to that alarm system. Sounds like there's an ignition kill feature in it somewhere.

Get the factory manual and then start taking that alarm off. Hopefully it doesn't have an outside key switch that will leave a hole in the fender.

 

Well, what I have is the HAynes for now, and I cannot get one too me fast enough
I feel it must be part of the alarm as well so gonna trace it all and I will keep everyone posted, anymore input gladly received.

 

when you cut the wire,did you have power on wire,or is it ground,

 

Powered, I am gonna spend some serious time today tracing stuff around again, this makes me NUTSO

 

Johnny,
You did not answer the magic question.........factory tach or aftermarket????
If it is factory the wire that goes to the aux term on the dist cap(coil) has a white factory clip with a very thin wire coming out of the harness on the firewall near the same spot where the positive feed for the distributor is.

 

Factory tach, I unhooked it at the back of the tach today and there are 2 pink wires and one white wire on a L shaped 2 prong female receptacle the back of the tach are the males, I can follow them to the top left of the fuse block, but it is butted right up tight to the kick panel, and appears that they are part of the harness that goes thru the firewall, but on the opposite side of the firewall NADA no white, no pinks etc.?????
This is kicking my butt and I am a pretty good problem solver !
Please keep ANY ideas coming gents!
How can I test the tach with any jumpers or anything to see if I can make it move ?
Thanks