Is corvette fuse/relay box needed with ISIS?

[Joe's GTM]

I have a question for anyone running an ISIS system for their electronics:

To my understanding, the PCM works independently of the ISIS system, but gets power routed through the ISIS solely for the ignition and the starter.

Since all engine electronics are run by the PCM and not the ISIS, will a Corvette fuse box need to be tied into the PCM/ engine harness, or does the ISIS take care of all respective fuses and relays?

Thanks,
Joe

[Rumbles]

I called ISIS Tech Support yesterday and asked similar questions:

• ISIS only provides 12V and a start signal to the ECM
• If you have a stock ECM harness, that provides all the circuits between the ECM and sensors (i.e. The eyes, ears & Brains)
• The missing link is the Fuse Relay box to power the heavy loads like injectors, O2 sensors, etc. (i.e. The Muscle)

There are vendors like Currentperformance.com who provide an after market fuse relay box replacement solution.

I'm wondering if I could simply use a stock GM fuse relay box from a doner car to provide "The Muscle".

Anyone tried that route?

[vtgtm]

I have Gen II #389 with an LS1 engine from a 1998 C5 donor. I am using the ISIS system with the stock engine harness and the underhood fuse box from the donor (I have swapped out the 1998 PCM for a 2002 PCM). The fuse box has been installed in the same location as shown in the GTM build manual. At the risk of oversimplifying, the ISIS system essentially replaces the Painless harness that comes with the kit. The ISIS system does add a whole bunch of other cool features depending on what you buy like push button starting, a security system, and much improved troubleshooting.

[Shane]

I second what vtgtm said. The UHFB ('vette Under Hood Fuse Box) will still be used as that is what the engine harness connector plugs into and also interfaces with the ECU. The UHFB is already configured for the ECU to be able to operate the cooling fans, injectors, AC compressor, etc, etc. The only reasonable way to get rid of the UHFB would be to buy an aftermarket engine harness, which would come with a smaller fusebox already attached. The upside is that it would make the wiring much easier instead of all of the splicing and work-arounds needed with the UHFB, and it would cut about 5 pounds of weight by eliminating the UHFB and all of the bulky connectors that go along with it. The downside is that usually the aftermarket engine harnesses do not come with any of the AC circuits wired, so you would have to wire all of that stuff from scratch....and instead of having relays for low and high speed cooling fan operation (like you have with the UHFB), it will just have a single relay for cooling fan operation.....both fans are either on or off.

And yes, as far as the ISIS is concerned, pretty much all it does is provide an IGN ON circuit to the engine harness.....so whether you use the Painless and send that ign on signal from the key-switch, or use the ISIS to send the ign on signal from a Powercell, the engine harness does not care which.

[Rumbles]

Ahhh, got it...thanks