[smfspeedemon]

help i just put a 450hp motor in my 88 vette and somehow the tac wire got cut off and i cant find it unfortantlly i need that wire for my msd to get spark does anyone know were that wire originates from so i can just run a new wire to the dist

 

[docvette]

Doc here, imp:

The Tach wire DOES NOT provide spark...

However , it will be the white wire from the body harness, that used to plug into the Old HEI unit..

Spark for your MSD will come from the Switched Ignition , a 12 gauge orange or Purple..It will only have 12 volts on it when the Key is on.

Doc imp:

 

[smfspeedemon]

i was told by msd i need that tach wire its the pulse wire do you know were that white wire originates from the body harness so i can just run a new one thanx smf

 

[docvette]

Doc here, imp:

Depending on what engine came out..

The White wire goes to the computer and the tach..nowhere else.

If your not running the factory computer than it will only go to the Tach.

The Pulse is an OUTPUT to the computer from the HEI, not an INPUT, and serves as a reference pulse for Computer signal coordination..should you be running FI, TBI, or EFI..and the whole sensor pack for the engine.

Doc imp:

 

[smfspeedemon]

its a tpi 350 with first electronics and aerosenser with a air senser computer that piggybacks into the gm computer afr heads ect. so thank you for your help so i can go to the harness leading into my comp find the white wire ad on to it and route it to the dist and that should solve the problem?

 

[docvette]

Doc here, imp:

That should do it if you didn't remove any stock modules.

Doc imp:

 

[smfspeedemon]

ain: there is about three white wires going into my computer from the main harness any idea witch one is the tach wire

 

[docvette]

Doc here, imp:

The only way your going to find that out, is to unwrap the harness bundle and follow the wire out...The stock diagram offers no information about it..just white wire from Tach to HEI module, then into the computer ...Pin D4..

It also shows no other white wire.

Doc imp: