Ignition Switch Wiring

[Hotrod1952]

I am using a wiring harness, ECM, & TBI engine out of a 1987 R20 in my 66 C20. I want to use the ignition switch from the 66 and integrate it into the wiring harness of the 87. I have looked at both diagrams and am a bit confused on a couple.


66 Switch----------Function------------87 Harness
Connector

Red----------------Battery + ------------Red - 2qty
Purple-------------Starter Solenoid------Purple
Pink---------------Distributor or ECM----Pink
Dark Green-------Ground- gauges?-----Tan/white - brake switch ground?
Brown/White-----Accy- Fuse box-------Brown and Orange?


Sound right???

[PGSigns]

You are going to need a later model higher amp capacity switch to carry the load like come with the American auto wire kits. The stock switch will not carry the load.
Jimmy

[66LSx]

Originally Posted by PGSigns

You are going to need a later model higher amp capacity switch to carry the load like come with the American auto wire kits. The stock switch will not carry the load.
Jimmy

Could always have one of the 12V+ switch ignition sources trigger a relay... which than on its high load circuit could carry the job of all of the 12V high-amp distribution. (fused/circuit breaked accordingly to load)

(on the 30->87 circuit)

[Hotrod1952]

Good call PgSigns. I never thought about the amps. Since my ignition key also works the doors I might have to look into a relay like 66Lsx mentioned. Do I have the connecting wires correct?

[Captainfab]

X2 on the relay.

[PGSigns]

I would have to sit down with the wiring diagrams for both trucks. That I don't have time for. You can get the switch you need and the connectors for it from AAW. I would do that over relays to keep it simple. Cost would be about the same. Your headlight switch is gonna be that same way. Gonna need a late model switch or the one out of the donor.
Jimmy

[ray_mcavoy]

Originally Posted by Hotrod1952

Good call PgSigns. I never thought about the amps. Since my ignition key also works the doors I might have to look into a relay like 66Lsx mentioned.

I agree with the recommendations of using the AAW switch or relays. I don't know for sure but I think you might be able to use your original lock cylinder in the AAW switch so you can keep your original key.

Originally Posted by Hotrod1952

Do I have the connecting wires correct?

Yes, it looks like you've identified most of the wires correctly. Just to expand on things a bit:

The 87 wiring is likely to have a yellow wire (instead of purple) running from the ignition switch "SOL" terminal to the neutral safety switch. It should transition to a purple wire for the section that runs from the neutral safety switch to the starter solenoid though.

The dark green and tan/white wires are both switched to ground to illuminate the "TEMP" and "BRAKE" warning lights as a "bulb check" feature when cranking the engine. Dark green is for the temp light and will not be needed if your truck has a temperature gauge instead of a light. Tan/white is for the brake warning light and will only be needed if you're adding one of these lights to your 66 cluster.

The brown/white wire is the alternator "exciter" wire and is a special resistance wire. If the 87 harness came from a truck that had factory gauges then it should have a similar brown/white resistance wire connected to the same terminal as the orange wire. But if it came from an 87 that had a warning light cluster then it will have the alternator "exciter" wire routed through the alternator warning light. You may or may not need this circuit depending on the alternator you'll be using.

[Hotrod1952]

Thanks for the great info! I did not know about the alternator exciter. I learn something new every day!

[ray_mcavoy]

You're welcome!

And a bit more info on that alternator "exciter" wire ... Most of the stock ones are a section of 2Ω per foot resistance wire that's about 5 feet long (for a total of about 10Ω). That's good if you're using a 10SI or 12SI internally regulated alternator. You'll need to add more resistance to the circuit if you're using a newer CS alternator though. And you won't have to worry about that wire at all if you're using a "1 wire" alternator.