Some general fusebox & wiring questions

[Coelacanth]

I finished installing my electric fuel pressure and boost gauges, wiring them in and checking/rechecking, then soldering everything up was not a fun ordeal I want to do often! Anyway, reconnected the negative battery cable, turned the key, and everything is working properly. I guess it helps to be painstakingly methodical.

I have a few questions about fusebox wiring following my install and some future plans. See the areas marked in green in the attached picture indicating what was changed.

-I used an add-a-circuit with 3A fuse in the ECM-IGN location "P" to provide switched power to both gauges.

-I added a 3A fusible link to a spade connector in BATT port "Q" to provide always-on power to the fuel pressure gauge.

-I grounded both gauges to the location marked "Z" at the top right of the fusebox, with a wire and eyelet I bolted down on top of the cylindrical capacitor that's already mounted there.

Question 1: Is the location "Z" a good ground location?

Question 2: I'd like to install a kill switch. I've read several topics on this already...is wiring a toggle switch into the ECM-IGN circuit in the fusebox a good suggestion? I'm already in there so I'd go that route if you guys agree that's a decent option.

Question 3: The fuel pressure gauge has an optional power wire that's suggested to tap into the headlight wire (brown) so that the unit dims 30% when the headlights are turned on. Is there an easier way to get at this wire--or a similar headlights-on power lead--than trying to get at it from the rear of the headlight switch?

Thanks as always for the advice!

 

[Coelacanth]

Anyone? Anyone? Bueller?

 

[RmvBfrFlght]

-I used an add-a-circuit with 3A fuse in the ECM-IGN location "P" to provide switched power to both gauges.

-I added a 3A fusible link to a spade connector in BATT port "Q" to provide always-on power to the fuel pressure gauge.

Not sure why you would want the fuel pressure gauge always powered. Could end up draining the battery.

Question 1: Is the location "Z" a good ground location?

It is an OK ground. I prefer a more dedicated ground, not subject to the plastic fuse block moving.

Question 2: I'd like to install a kill switch. I've read several topics on this already...is wiring a toggle switch into the ECM-IGN circuit in the fusebox a good suggestion? I'm already in there so I'd go that route if you guys agree that's a decent option.

That works, pull/open that fuse and it won't start.

Question 3: The fuel pressure gauge has an optional power wire that's suggested to tap into the headlight wire (brown) so that the unit dims 30% when the headlights are turned on. Is there an easier way to get at this wire--or a similar headlights-on power lead--than trying to get at it from the rear of the headlight switch?

Try using the LPS tap, as long as the instrument panel lights are on bright enough it should work. Getting to the headlight wires isn't easy.

RemoveBeforeFlight

 

[Coelacanth]

Not sure why you would want the fuel pressure gauge always powered. Could end up draining the battery.

It's in the installation instructions; I presume it has a memory save feature, but it probably consumes very little power.

That works, pull/open that fuse and it won't start.

Thanks, I'll probably go that route.

Try using the LPS tap, as long as the instrument panel lights are on bright enough it should work. Getting to the headlight wires isn't easy.

Thank you again. So I assume the LPS tap should work as long as the headlight dimmer switch is all the way up (which it always is, anyway)? I realize that LEDs are typically not dimmable because they work with only a very limited voltage range.

 

[RmvBfrFlght]

It's in the installation instructions; I presume it has a memory save feature, but it probably consumes very little power.

Seems odd, but if that it what is called out in the instructions, then should go with it.

RemoveBeforeFlight

 

[Coelacanth]

Update on wiring: Everything except the killswitch is working exactly as desired. I wired the fuel pressure gauge, tapping into the LPS circuit as suggested by RemoveBeforeFlight, and it is working perfectly with the headlight dimmer turned all the way up. When this wire is connected, turning on the headlights makes the gauge's LED lighting dim by 30%, and it works perfectly. Thanks, that was too easy--a helluva lot easier than trying to splice into the brown headlight wire or switch.

Working on the killswitch was confounding me, though. It looks like the only way I'll be able to wire it in properly is to remove the fusebox so I can access the wire leading to the ECM-IGN fuse circuit...unless there's an easier way to locate this wire? I decided not to do a fuse tap or inline fuse bypass because it would be obvious just by looking at it that something was modded. Other than behind the fusebox, is there an easier way to tap into the ECM-IGN wire?

 

[RmvBfrFlght]

Update on wiring: Everything except the killswitch is working exactly as desired. I wired the fuel pressure gauge, tapping into the LPS circuit as suggested by RemoveBeforeFlight, and it is working perfectly with the headlight dimmer turned all the way up. When this wire is connected, turning on the headlights makes the gauge's LED lighting dim by 30%, and it works perfectly. Thanks, that was too easy--a helluva lot easier than trying to splice into the brown headlight wire or switch.

I thought you'd like that method.

Working on the killswitch was confounding me, though. It looks like the only way I'll be able to wire it in properly is to remove the fusebox so I can access the wire leading to the ECM-IGN fuse circuit...unless there's an easier way to locate this wire?

Yes, behind the glove box, to the right is a clear-ish connector. Location F has a PNK/BLK wire (only one in the connector). That is the wire fed by the ECM-IGN fuse. Open it and a no-run will occur.

I decided not to do a fuse tap or inline fuse bypass because it would be obvious just by looking at it that something was modded.

I was thinking the same, but if the hush panel was back in place it might have been OK.

RemoveBeforeFlight

 

[Coelacanth]

Yes, behind the glove box, to the right is a clear-ish connector. Location F has a PNK/BLK wire (only one in the connector). That is the wire fed by the ECM-IGN fuse. Open it and a no-run will occur.

That's awesome, thanks! What do you mean by "Location F" though? I already have the glovebox out so this should be easy to find and splice in a switch.

 

[GNRick]

Whats a "Hush Panel"?

 

[RmvBfrFlght]

That's awesome, thanks! What do you mean by "Location F" though?

The terminals in all connectors have a position location. Such as the ALDL terminals A & B which get shorted together for various reasons. And the ECM harness connectors are also labeled by location within the connector.

The location is usually molded into the connector body.

RemoveBeforeFlight

 

[RmvBfrFlght]

Whats a "Hush Panel"?

A molded plastic panel with jute glued to the top of it that is mounted under the dash. There is one for the driver side and another for the passenger side. The purpose is to reduce the level of noise emanating from under the dash into the passenger compartment. Hey, it's a Buick isn't it????

As with my car when obtained, they were long gone...

RemoveBeforeFlight

 

[GNRick]

Oh, so thats what its called? Kirban used to sell one made out of fiberglass. Wish I hadn't sold it with the car

 

[Coelacanth]

The terminals in all connectors have a position location. Such as the ALDL terminals A & B which get shorted together for various reasons. And the ECM harness connectors are also labeled by location within the connector.

The location is usually molded into the connector body.

RemoveBeforeFlight

I just wanted to thank you for your help with my wiring project. I think I spent 3 hours messing around with a 3-prong, small round rocker switch and the damn thing just wouldn't work (actually, it worked...ALL the time!). No matter which position the switch was in, the car would start. After all this hassle it turned out that the switch was defective.

The pink wire with black stripe was very easy to get at...5 bolts to remove the glovebox and plastic cover and towards the right side, in the big clear connector, there it was.

I got a new 2-prong switch and badda-bing, I had it working in 15 minutes. I decided to keep the defective switch mounted; even though both are pretty hard to find, the defective one is a bit more likely to be found and makes a great red herring. I love how it works...flick a switch and everything looks fine, everything powers up...but the car just turns over and over but won't start.

 

[turbojay]

Cool idea with the kill switch.

 

[Coelacanth]

Well, I did a test run last night and everything appears to be reading correctly with the gauges. The electric boost gauge read up to 14 PSI, blipping briefly at 15 PSI at WOT...running stock boost, that seems bang on. The fuel pressure gauge with transducer on the fuel rail seems to pretty closely match the readings from the gauge on the rail, ~43 PSI at idle with line off. With AXiS interface and TurboTweak chip, everything seems dialed in.

I should be hitting about 57 PSI fuel pressure at WOT, correct?

 

[gnX405]

Well, I did a test run last night and everything appears to be reading correctly with the gauges. The electric boost gauge read up to 14 PSI, blipping briefly at 15 PSI at WOT...running stock boost, that seems bang on. The fuel pressure gauge with transducer on the fuel rail seems to pretty closely match the readings from the gauge on the rail, ~43 PSI at idle with line off. With AXiS interface and TurboTweak chip, everything seems dialed in.

I should be hitting about 57 PSI fuel pressure at WOT, correct?

Yes, FP while in boost should equal boost pressure plus pressure read with line off. In your case 14 + 43 = 57


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[Coelacanth]

Thanks John. I wasn't sure if max fuel pressure would be pressure with line off plus max boost...or fuel pressure while driving (it drops from 43 to 37 or so with line on) plus max boost...which would be in the low 50's.

 

[bpman1234]

Wow so if running 55 line pressure. Line on.and hitting 25lbs of boost .it should be 80 lbs of fp?

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[bpman1234]

Sorry forgot to mention this is on e85.

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