Inertia Switch and Continuity Help Please

[Oldguy33]

Going crazy chasing continuity issues between frame ground, IGN switch and related wires going to the IGN FEED at the fuse panel.To make a long story short, I found that with the inertia switch set to on ( pushed down) I will get approximately 76.5 ohm readings at multiple location as mentioned above as well as at battery cable points. If I remove or shake the inertia switch to brake the connection, there is no longer continuity between frame ground and related IGN wires, coil wires and battery cable connections.
Why am I consistently reading 76.5 ohms with the inertia switch plugged in and in the on position?
I should mention the following while testing continuity:
Ron Francis wiring harness, no battery, rear harness disconnected, dash harness disconnected, front harness disconnected and steering column disconnected.
Please help before I loose my mind.

[narly1]

Hmm. One step at a time.

So with the inertia switch and ideally it's entire circuit isolated from the car, what is the resistance to ground between your various grounding points and the battery -ve post? Even better what is the voltage between those points and battery -ve?

My gut tells me you have a bad grounding situation and everything is being grounded through the inertia switch. Look for insulating paint, and broken/loose wires at your ground connection points.

Earl

[i.e.427]

All you are doing is reading through the coil of the relay for the fuel pump........... or not. Without power to the chassis harness, what you are doing tests nothing.

[Oldguy33]

Thanks for your input. Other than checking my grounds for contiunity I agree that I was chasing rabitts in the electrical system w/o voltage applied. The resistance is minimal so my plan is to connect the battery and check the circuit in question. Thanks again.

[edwardb]

Quick explanation of the inertia switch and how it's used. Maybe obvious from studying the schematic. But FWIW. The RF panel fuel pump circuit has a relay that's energized when the ignition power is on and sends +12V to the fuel pump. The ground for the relay goes through the inertia switch. All normal (e.g. inertia switch button down) the ground circuit is completed, the relay is closed with ignition on, pump will run. If the inertia switch triggers (e.g. hard bump, collision, etc.) the button pops up, the switch opens, ground to the fuel pump relay is interrupted, fuel pump relay switches off. Easy enough to test with power. You could test continuity through the switch, but doesn't prove too much.

[Oldguy33]

My issue is reading continuity between battery cable connections and frame ground after eliminating all other sources for the issue. I guess the 76.5 ohms can be expected between frame ground and battery cable so I'll apply voltage and check.

[JohnK]

That doesn't sound right, IMO. I checked every ground connection I made with a DMM and they were all in the 0.1 - 0.2 ohm range (i.e., the same number I get if I just touch the two leads of the DMM together). 76.5 ohms is waaaay too much resistance for a proper ground connection. Double check that your DMM leads are OK. What number do you see when just touch the two leads together?

[Oldguy33]

The problem is reading resistance from frame ground to the positve battery cable, no battery installed. I suspect that somehow I am pcking up a resistance of 76.5 ohms from the inertia switch relay.

[Papa]

There is no relay in the inertia switch. It's simply a set of contacts. It's either open or closed. The relay in that circuit is the fuel pump relay as Paul described. If you suspect that is your source of resistance, pull the relay. I'm still tying to figure out what you're trying to do. All the circuits in the electrical system are between the chassis ground an positive battery cable.

[JimLev]

I think your over thinking this. Your testing between the frame and the + battery cable shows you don’t have a direct short to chassis ground which is good.
Soldier on. Connect the battery and see if the fuel pump runs.

[Oldguy33]

Thanks for your input. Other than checking my grounds for contiunity I agree that I was chasing rabitts in the electrical system w/o voltage applied. The resistance is minimal so my plan is to connect the battery and check the circuit in question. Thanks again.

[Mastertech5]

You cannot test resistance in a circuit when powered, ground or otherwise. If you're testing continuity from ground to pos battery cable you are going through a component and measuring resistance of that, normal. Pull the fuel pump relay and test to from the relay ground terminal, which goes through the inertia switch, and the negative battery cable disconnected or any other body ground. It should read 2 ohms or less. If not check all your ground points as previously stated.

[Oldguy33]

No issues with the battery connected. Chassing resistance was a waste of time as some pointed out. Thanks for all the support and guidance from the forum members that rsponded to my questions. I Installed a couple extra fuse panels, one hot and the other switched and now on to more wiring.