Gauge Cluster Conversion - Truck Now Dies - Help!!

[1972BlueC20]

So i did my conversion from an idiot light dash to a full cluster dash with tachometer, I followed all the instructions online and with help from people on this forum.

All my gauges are working but I'm having an issue with my truck dying when I drive it. It will idle all day and even rev in park, but once I start driving it will die at different times.

Thought I had a loose wire going to the HEI, so I made sure it was solid, still dying when I try to drive the truck. I didn't mess with the wire going to the HEI during the conversion other than I probably bumped a lot of stuff back there while installing the copper line for the oil pressure. I know it's a problem with spark because the first time it died, I took # 1 spark plug wire off the spark plug and had no spark....I then wiggled the wire feeding 12v to the HEI while my wife turned the key and it eventually started back up. Since then I have used the proper HEI harness plug end that I spliced into the 10 gauge wire going from the bulkhead to HEI (original resistor wire was replaced with a 10 gauge wire) It had worked for over a year no problems until I did this cluster conversion.

Is there anything that could of caused this related to the gauge conversion?

Any help is greatly appreciated!

[mgore68]

Just a guess, but could your wire to your Tach be grounding out?

[1972BlueC20]

Originally Posted by mgore68

Just a guess, but could your wire to your Tach be grounding out?

I don't think so.

Pardon my lack of electrical knowledge, but if it was grounding out would that cause the truck to die?

[mgore68]

Like I said, its just a guess. Just thinking if the wire to the distributer grounded out it may kill it.

[leddzepp]

Where is the HEI plugged in on the fuse panel?

[Coley]

Originally Posted by 1972BlueC20

I don't think so.

Pardon my lack of electrical knowledge, but if it was grounding out would that cause the truck to die?

Yes...if you ground out the coil...the truck will not run.
Are you using rubber grommets or equivalent in going through the metal firewall of the truck?
If any of the tach signal lines are rubbing on metal somewhere and grounding out your vehicle will stop.
What did you hook the main power feed for the tach up to?

Coley

[1972BlueC20]

Originally Posted by leddzepp

Where is the HEI plugged in on the fuse panel?

I just replaced the original resistor wire that went into the bulkhead with a 10 gauge red wire with the correct terminal like what was on the end of the resistor wire. It worked perfect and was giving 12v for over a year until I did this cluster conversion.

[1972BlueC20]

Originally Posted by Coley

Yes...if you ground out the coil...the truck will not run.
Are you using rubber grommets or equivalent in going through the metal firewall of the truck?
If any of the tach signal lines are rubbing on metal somewhere and grounding out your vehicle will stop.
What did you hook the main power feed for the tach up to?

Coley

Yes the lines aren't touching any metal at the firewall. The tach power source is the positive side of the fuel gauge. I was instructed to do this by either VetteVet or TBone1960 I can't remember. Tach works perfect.

[leddzepp]

When you wiggled the wire it started up...I'll bet there is a loose connection at the bulkhead, and it cuts out. I had a similar problem. I ran a wire from inside the cab at "ignition unfused" port and it solved the problem.

[1972BlueC20]

Originally Posted by leddzepp

When you wiggled the wire it started up...I'll bet there is a loose connection at the bulkhead, and it cuts out. I had a similar problem. I ran a wire from inside the cab at "ignition unfused" port and it solved the problem.

Good idea but all my IGN unused are full. Any good way to split them off to make room for 1 more wire?

[Davidf]

I'm in the "tach is grounding out the ignition" camp. Way back when, I did a full restoration on '73 BMW 2002. Engine would start fine cold, but almost impossible to start when warm. It took multiple indy shops (since I failed) to figure out I had wired the tach backwards and was grounding out the ignition system. Incidentally, the tach worked fine.

[1972BlueC20]

Here is a pic of how my tach is wired up in the back.

I'm using a tach filter.

I have a ground running from the G post on the back of the tach to a bolt on the back of the cluster that is metal.

I have a wire running from the 12V post to the power side of the fuel gauge.

Then the yellow wire runs through the tach filter, and comes out to a red wire which I ran straight to the dizzy.

The tach filter also has it's own ground which I ran to another metal bolt on the back of the cluster.

I was told this was ok before I did this by several people on this forum