Could a short of the IGN 1 wire at the ignition switch end (the 16 gauge dark blue wire w/ white tracer that runs from the ignition switch to the ignition side of the voltage regulator underhood) have caused my water temp and fuel gauge to have burned out? The first few inches of my IGN1 wire had the insulation melted off. there is another blue wire (18 gauge) at this end that is ganged together at this connection on the ignition switch that runs up to the instrument cluster... this sounds linked to me.

If this is the case I need/want to figure out whey the IGN1 wire failed. Could accidentally grounding one of the coil leads for a few seconds have caused the IGN 1 wire to melt at the ignition switch?
Everything else that is relatively inspectable seems fine. I took the instrument cluster out and have examined parts of the underhood harness, but have limited access... I cut into the harness tape and the melted IGN 1 wire appears for the first few inches (ignition switch end) then as it goes towards the bulkhead it is no longer melted (can't gain access all the way to the bulkhead though... engine side is all good)


Thanks in advance

The "-" side of the coil gets grounded when the points are closed , so I'm a little confused ... but taht shouldn't be a surprise to anyone ...

I melted that wire a few years ago. No one could tell me why. I couldn't find a reason. When it happened my ammeter was going from an extreme charge to an extreme discharge rapidly, and it would only do it accelerating under a load. The only reasons I could think it melted was that I had hooked my coil directly to the ballast resistor, the had recently installed a Mopar Performance blue voltage regulator, and/or my field wire on my alternator had a crack and shorted against something.

I changed my engine wiring harness and repaired the dash harness. I changed the alternator too. I also went back to a regular style voltage regulator and wired the choke differently.

A few weeks later the battery developed a dead short.

maybe it was the +... it was an error so now thinking back I can't remember for sure ex except that I forgot to put 1 of the wires back on the coil and it grounded to the engine... i am running a pertronix under cap module.

Car is a 71 B body?
This is what I'm seeing.
Accidentally grounding the + coil wire WOULD melt the IG1 blue wire if the ignition key was taken to run position:
Significant current would be drawn from the big red wire feeding 12v to the ign switch, over to the big blue wire when the switch is in run position, through your ballast resistor and then to ground via the accidentally grounded + coil wire.
Check your ballast resistor at some point.

I don't see how it could fry the gauges though. I assume the smaller blue wire you mention coming off the ign switch feeds the dash limiter/regulator right? I don't see a damaging current flow path through that dash regulator because of the accidentally grounded wire.
Are the gauges actually bad? And/Or the regulator?

I agree there appears to be "a link" if the failures occured simultaneously but I can't see it at this time.

car is a 69 b-body.

fuel gauge and water temp gauge are toast (don't respond to +3 V across their back posts... the voltage limiter puts out a full 12 volts (instead of 5 v) when it has 12 volts of input.

my ballast is gutted and the resistor is replaced w/ a piece of 12 gauge wire since i run a pertronix module. I assume in this case as long as i have continuity across the ballast posts I am good to go...

is pulling the whole underhood harness overkill at this point to check for damage... last thing in the world I want to do as this car has AC so getting to the bulkhead is a pain in the neck (car has A/C... just not sure how likely it is that the only issue is the first few inches of the IGN1 wire... anyway to assure the underdash harness is good without removing it? I previously had pulled the harness and everything looked great (of course this was before i accidentally caused the underhood short...).

I have a 70 Challenger and if I were in your shoes I'd approach this in stages:

- I would not remove and untape my harness (engine or dash) unless I saw signs of overheated wiring. Do a close visual inspection of the wires from the alternator back to the firewall bulkhead and regulator. Inspect the bulkhead connectors carefully at the engine compt side also for overheating/discoloration.

- Do ohm meter checks to verify the affected wires are not grounded etc.

- Repair and test the gauge cluster. This test can be done by setting it on your inner fender and connecting +12 battery power to it and simulating the sending units with resistors. I can explain more if needed.

- After all checks and repairs (ign sw wiring) are done I would leave my gauge cluster +12 volts disconnected (at the regulator/limiter)if possible and with the battery connected normally, turn ign switch to on and check for 12 volts at the ballast resistor terminal. All the while listening and smelling for smoke etc.

- If all that is good I'd connect +12 to the cluster limiter and turn the ign key on while staring at the gauges, ready to shut off the ign if any problems noted.

I would not tighten the battery terminals incase I needed to quickly disconnect it.

I'd be willing to phone talk to you about this if you'd like to. PM me for that. Jef

Thanks for your response. I'll run through your list and check things off one by one. So far everything else I have looked at looks fine ...

The main thing that bothers me is we don't understand why the gauges fried. It certainly seems related to the grounded coil wire though.

Once you are ready to connect the battery and turn on the ign switch for the first time, leave the regulator/limiter removed but plug in the harness to the dash panel. I think you can do that based what I see online. That way the ammeter will me connected but not the Temp and Gas gauges. I think you could even start the car that way.

Just want to make sure everything is good before hotting up the gauges.

I ran through all the contacts on the ignition switch plug end of the under dash harness and the connector end that plugs into the back of the instrument cluster (the circular plug end that mounts to the various pins on the back of the cluster)... All look visually good and checked out appropriately for continuity where there should/shouldn't be continuity. So I think the under dash harness is good to go now (I ran a new IGN1 wire from the ignition switch plug end to the bulkhead connector on the engine harness and visually inspected the engine side closely)...

I can't explain why the gauges blew either when the IGN1 shorted, except that my RT-Eng voltage limiter no longer steps voltage down to 5 V? May never know if the 2 are linked?

Thanks

I do this kind of work for a living, troubleshooting instrumentation, these kind of problems are fun to try and figure out (at least to me).

I wonder if that grounded wire may have done some making and breaking against the intake manifold and resulting spikes fried the high tech RT limiter putting full 12 volts to the gauges.

Either way I think your good work so far will have you up and running soon.
Jef