Gauge wiring gremlins

[Matt G]

My 74 Scout 2 has been pretty gremlin-free electrically, but I have one now and I'm not sure where to start. The Scout recently sat for 10 days while I was on vacation. I came back yesterday and started it (fired right up ) and went for a spin.

Symptoms
- while driving I noticed the blinkers weren't blinking.
- when I got back (in the driveway, motor still running) I noticed that activating the blinker causes my tachometer to cut out.

The above 2 sounds like some kind of grounding issue to me. The tach is an isspro gauge I bought from ihon which has worked well for almost 2 years, so I'm confident in the wiring I did immediately behind the dash. But - novice that I am - I'm a little mystified about all the power routing through the ignition switch, fuse panel, etc., which is all stock.

It was late and I just shut it down for the night, but I need to get on it today. So my question: any advice on where I should start?

2 other tidbits that May or May not be related:
1) I have had a problem with the oil pressure gauge cutting out intermittently for several months. But not in response to anything I do like blinker actuation. The other gauges (all isspros installed at the same time) work fine.
2) I also noticed while parked in the driveway that the engine rpm jumped way up to near fast idle territory (1200-1300) even though the engine was fully warmed and I'd been driving for 10 minutes. I'm not sure how an electrical gremlin could cause that so it May be unrelated, but that's never happened before.

 

[Scoutboy74]

Matt - I'd start by checking through the following with your engine off.

Engage your 4-way hazards. Do all associated lights both interior and exterior flash at a normal speed?

Turn your key to acc and select your directionals one at a time to verify proper illumination and flash interval.

If you didn't know already, there are two separate flasher fuses involved. One for ts and one for 4-ways. The above test is just to make sure both of your flasher fuses are still good and all your lights are functional.

The interference with the tachometer while the engine is running could well be a grounding issue. The ts and tach both receive power from the ignition switch or fuse block. Depending on how you wired the tach, you might even have them on the same circuit. I'd carefully examine your tach connections under the dash also.

So your oil pressure gauge...is that a stock unit, an aftermarket mechanical, or aftermarket electric? I'm guessing am electric, but not sure by your description. A mechanical gauge wouldn't cut out unless there was no pressure in the line, so I guess that choice can be ruled out.

Is your carb an electric auto choke or ???. Perhaps the throttle linkage bound up for some reason. Weak throttle return spring?

 

[Matt G]

Good suggestions trev, thanks.

First, clarifications. I replaced all the stock gauges a couple years ago with a complete isspro set from ihon; see pic below. So your guess about the oil pressure gauge is correct: it's an aftermarket electric gauge. I wired the new gauges in at Mike's place from scratch, but the rest of the vehicle wiring harness is stock.

Now, the tests: I did as you suggested this morning, and of course the problem has vanished. The 4-way (hazard) and turn signals all function correctly whether the engine is running or not, and the tach works fine. So the flashers can be ruled out as problematic.

I'm starting to think I have a power supply problem behind the dash, somewhere in the wiring that I did. The intermittent cutting out of the oil gauge is one issue, but I also have a couple dash indicator lights (brand new) that don't function, while others do. And now the tach has cut out at least once. I think I'll start by pulling the dash out and checking the bazillion crimps I made back there.

Gosh I hate electrical problems...

 

[Scoutboy74]

Thems real purdy. Good luck finding your gremlin.

 

[Matt G]

Thanks! I like the way the dash turned out.

No luck on the gremlin though. I verified with a test light that I have good power to an indicator light that isn't working, as well as to the oil pressure gauge. So now I'm thinking I May have a series of unrelated problems.

The oil gauge issue May be a problem with the sender itself

the indicator light in question is for the left ts. The exterior ts lights illuminate, but the dash indicator light does not despite receiving power. So this May be... Just a bad light?

That's all I was able to get to with disconnecting everything and ripping the whole dash out, which I don't have time for right now. I have new carpet and floor insulation I;d rather be putting in the Scout right now, but it's my dd so I need it operating reliably!