Background:
The car is a 68 w/ HEI powered by a relay triggered by the original coil feed wire. It also has aftermarket rally pack gauges installed, that function when the fuse is installed.

Symptom 1:
If the fuse in the "GAUGES TRANS" (lower right of fuse block) is installed, the engine keeps running when the key is turned off. It turns off fine when the fuse is removed.

Symptom 2:
With the car off, key in "run", and "GAUGES TRANS" fuse removed, the gauges have power. Not enough to function, they just move off of zero to a static spot.

Between 1 and 2 above, it looks like there is "stray" voltage on both sides of the fuse in that circuit. Voltage readings confirm this (with fuse removed). Does this mean I have a bad fuse block, or is there an alternate explanation?

I spent about 4 hours out in the heat trying to figure this out, would be appreciative of any pointers. I've attached my readings/notes.

Thanks.

 

 

Sounds as if a diode in the right spot may cure the issue.

 

There is always room for error, but I think that because the relay acts correctly w/o the fuse in that it is not wired incorrectly. I agree w/ the back feeding voltage.

Thanks for the reply.

Should have been more specific - it is an aftermarket rally pack set from The Parts Place Inc. Nothing is connected to the an IGN terminal on the fuse block (not sure a '68 has one (?).

I tried to figure out what devices have power and are connected to the gauge circuit - the ignition switch, the voltage regulator, and the light switch all do, but I don't understand how they could. I took readings on the brown wire to the voltage regulator hoping it would match what I was seeing at the fuse block but they were different.

 

Try connecting the relay for the HEI through the IGN terminal or a key switched spade terminal in the fuse block.

The ignition switch pink wire supplies power the resistance wire as well as supplies power to both the GAUGE and the DIR SIG/ BACK UP fuses. The Gauge fuse supplies power to the TCS switch, idiot gen light, temp gauge, oil pressure gauge, fuel gauge, and parking brake/ brake level light. Again the gen light or meter circuit has the brown wire feed from the voltage regulator connected to it. If the fuse is pulled and the key is on voltage will flow through the meter and back into the circuit.

Its a pretty simple circuit and you should not have any back feeding unless you wired the gauge cluster wrong.

 

Is the HEI powered by the resistor ignition wire? If so,that's wrong. HEI's use straight 12 volts.

 

He said a relay that supplies 12v to the HEI is powered by the resistance wire.

 

Why would you run the 12v feed to HEI through a relay? This does not make any sense too me, why reinvent the wheel?

 

 

No MSD box.

I ran the trigger wire to the relay off of a switched IGN terminal on the fuse box (for some reason I thought there wasn't one on this fuse box, I was wrong). That addressed the symptom of the engine run-on.

Doesn't mean I'm done (I still need to understand the what and why of the voltage backfeed), but at least I can drive the car normally and read the gauges

Thanks for the help.

 

Glad you got it drivable, double check your wiring for your aftermarket gauge setup. I bet that's the culprit. By all means it should have worked as wired off the resistance wire.