Andy1

For the switched hot to the PCM, how much current does it draw? What size fuse should I use (is a fuseable link prefered and why)? Should I consider a relay for this circuit? Finally, what is the wire gage size for this hot wire?

The link to my Fbody wiring diagram is no longer active, hench my questions.

Thanks,
Andy1

ryanvv355

iTrader: (17)

15 amp fuse should do the trick. 18 or 20 ga wire. I would use a fuse over a fusible link becasue if you blow your fuse out in to boonies its easier to fix on the spot, if you dont have bigger problems of course.

HDon22s

iTrader: (2)

If you put a 15 amp fuse on a 18-20 guage wire you better take wire to the boonies cause the fuse will be fine. The wire will need replaced. The best thing if you don't get a solid answer is to run the car with a amp meter inline and see what it draws. That way you will get the correct rated fuse and it will do it's job of protecting the components and the wiring. There is smoke installed in all electrical wiring and components. the reason for a fuse is to blow out before you let the smoke out. LOL. It could be very poss. it takes a 15 amp fuse but the wire will need to be in the 12-14 ga. size. Did you try checking a oem fuse block or dia. for the correct size.

dsrour

18 gauge wire would be conservative. GM uses 20g for PCM power.
Using a relay is the best way to save your ignition switch. Definitely would not use fusible link.

HDon22s

iTrader: (2)

There's some good info.

Andy1

Thanks for the diagram. I've got a reworked harness (Wait4me) and the constant hot wire is small (20ga?). The switched hot wire however is something like 12 or 14 ga. I've never wired a relay for ignition on, but your "save your ignition switch" comment seems prudent.

BTW, I need to map out some existing circuits and need to know the wire gages. Is there any kind of chart (or link to) that cross references the copper strand bundle diameter with its gage size?

Andy1

dsrour

Here's converion table for wire size.
For the relay pins 85 and 86 are the control coil. one side is ground and other gets 12 volts when ignition on. Very litle current required. The power circuit part gets battery 12 volts to pin 30 and pin 87 goes to load, pcm in this case. hope this helps.