Weird electrical "issue"

[dabobbo]

I'm installing my scanmaster and an electric fuel pressure gauge (Prosport Evo) on my '87 GN and I'm seeing a weird problem with the gauge where it is flickering - not on and off, but not staying bright. I think I've pretty much ruled the gauge out, putting 12v directly to it works fine, and the gauge is strong and steady.

The weird thing is, when I let the car sit for about 10 minutes and turn the key to acc, the gauge lights up just fine and is strong and constant, but when I start the car it starts to flicker, and does so even if I go back to acc. 10 minutes later it's again fine on acc until I start the car. I've tried several different grounds under the dash, same issue.

The scanmaster works just fine. I'm pulling power from IGN1 in the fuse box for both the scanmaster and the FP gauge. Anyone seen something like this? Thanks!

Bob

 

[T- Type Tim]

How's the ground wiring look?

 

[Nick Micale]

If you like your Scanmaster and other gauges to give you accurate readings, the grounds must go directly back to the battery, not taking a ground path through the dash and body?

Since the main battery ground cable is connected to the engine, the cast iron block is a better conductor than somewhere on the body. NEVER consider using the frame for any ground as it is a very poor conductor, and not even connected to the battery.

When building race cars, GN's in my case, ALL critical electrical components like the computer, fuel pump and others are always routed direct to the battery for the ground, as well as all their power leads.

 

[dabobbo]

Thanks Nick, I'll try running a ground line right to the battery this week. Right after I posted it started raining here so I took the car back to where I store it. I still need to hook up the sender too.

As far as I know my grounds are good, never had an elecrical problem before. I guess this gauge is a bit more sensitive to power than my other non-digital gauges.