Quote:
Originally Posted by Vince@MSperfab
If it is the factory style switch in the dash it will provide zero voltage while cranking. This system ran 12v cranking voltage from the resistor bypass on the starter.
You can run a relay with a diode to use the purple starter wire as a signal to send 12v to the ignition circuit.
Vince
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You don't need any additional relays or diodes.
I've done 5 LS swaps on 1st Gens all with factory ign switches. 3 GM Perf Harness, 1 Psi and 1 reworked GM take out harness.
LS ECM
You need 12v switched power to the PSI fuse box.
The ECM is powered up with ign 12v. When you turn the key on the ignition and fuel pump relays close.
When you hit start the purple wire provides 12v to the starter.
From PSI
NO-START
1. Red Ignition Wire (From back of Fuse/Relay Center) has 12-volts with the Key in the ON
position and CRANKING position. This cannot be stressed enough, most NO-START
conditions can be traced to this wiring issue.
2. Check that 2 Large Ring Terminals by Crank Sensor are connected to CONSTANT POWER.
Batt. Battery Positive (2 LARGE RING TERMINALS COVERED IN BLACK HEAT
SHRINK),
These are often mistaken for ground wires because of the black heat shrink