Help - Electrical Gremlins

[Stumper]

I’ve had my battery neg disconnected for the past week while I installed a new dash. Today after getting done wiring up a new oil pressure gage and an oil pressure pressure sending unit for the idiot I reconnected the battery neg terminal and immediately went up in smoke. The hot wire from the starter to the relay and from the relay to the bulkhead terminal fried big time… No other wires were burnt, nothing under the dash burned or got hot. The hot and ground connections to the new dash were fine, and correct. I took the starter out and bench tested it with a spare battery. It fully spun and engaged - although sounded a bit “loud” - but it is one of the original big starters. My big dilemma is what the heck happed to cause the wire to burn up like that???
I suck chasing electrical problems and could use some help. If the relay on the dash just decided to stick, would that have done it? If the starter was bad and grounded I wouldn’t think it would run on the bench? At this point I assume the relay is bad and needs replacing, obviously the burned line. My Buddy has a starter that I could use if we thought it was the starter. Any thoughts, ideas or tips on what/how to find my gremlin?

 

[pnora]

You have something in the dash or wiring grounding out. The wire was most likely the fuse link. Starter has nothing to do with the problem. Take apart what you put back and inspect closely.

 

[Stumper]

The two things I changed was adding a mechanical oil pressure gage and wiring up the light in it. It was wired to a switched hot with no switch on and there was no sign of heat or damage. I also added an oil pressure sending unit for the idiot light and again no sign of line damage. These were the only electrical changes I made while the car was down. The new dash panel I put in was wired the same as the one that came out.
‍

 

[pnora]

The two things I changed was adding a mechanical oil pressure gage and wiring up the light in it. It was wired to a switched hot with no switch on and there was no sign of heat or damage. I also added an oil pressure sending unit for the idiot light and again no sign of line damage. These were the only electrical changes I made while the car was down. The new dash panel I put in was wired the same as the one that came out.
‍

You did not have the problem when you took it apart. There is your clue. Something is being overlooked.

 

[Stumper]

I could not see any sign of wire damage under the dash anywhere. The only burned wire was the hot from the starter to the relay and then the hot from the relay to the bulkhead.

 

[pnora]

I could not see any sign of wire damage under the dash anywhere. The only burned wire was the hot from the starter to the relay and then the hot from the relay to the bulkhead.

You have something grounded. Pinched or wired incorrect. The point is you created a dead short to ground. If the key was off when this happened that would indicate a 12 volt non keyed circuit. Ammeter would be a good point to inspect.

 

[Don Frelier]

Ammeter is the place to start.

 

[Stumper]

What would I check with the amp meter (remember I suck with electrical).The red hot wire goes to the terminal marked Red on the panel for the gage and two black ground wires that go on the terminal next to it. Could the gage itself be grounded out internally? How can I tell?

 

[pnora]

What would I check with the amp meter (remember I suck with electrical).The red hot wire goes to the terminal marked Red on the panel for the gage and two black ground wires that go on the terminal next to it. Could the gage itself be grounded out internally? How can I tell?

The black wires are not ground wires. Did you attach a wire there?

 

[Stumper]

There are two heavier gage black wires that were on the post adjacent to the “red” post on the previous dash. I just put them on the same post with this dash. The previous was working fine. This is on my 62 Fury by the way.

 

[Don Frelier]

Remove all the wires from the ammeter and test each post for continuity to ground.
It's likely you'll find that the ammeter is shorted to the dash. The posts need to be isolated from the metal frame.

 

[Stumper]

Thanks guys. I’ll pull the dash out later and check. Will report back….

 

[Stumper]

Didn’t get around to pulling the dash today to check continuity but I plan to do it. I made up new wires today while a buddy crawled under the dash. He didn’t find any burned or damaged wires and confirmed that they were on correct terminals.
My SM diagram shows the red terminal wire on the amp gage going to the bulk head connection to pick up power from the red line coming in at the fire wall - the one that burned up. It shows one black wire from the other terminal that goes to the bulkhead to pick up a black wire that runs to the alternator. I still haven’t figured out what the other black wire is for that is on the same amp gage terminal but did find that it splices into a green wire …. Still need to trace some of these wires out.
That said, what ever the wires go to they were attached to the old dash panel the same way and it worked fine. So maybe I’ll find that the amp gage itself is bad and can get it replaced.

A couple of how to electrical questions. Since the wire from the starter to the relay and from the relay were burned to a crisp, is it likely the relay is also toast? How would you test it?

If a starter is shorted out internally it wouldn’t work on a bench test would it. Could the short that bad come and go in a starter?

When checking continuity of the amp gage terminals is it ok for the dash panel to be removed since you are going terminal to frame anyway?

Thanks in advance for the help!

 

[Don Frelier]

You can test the ammeter connection posts to the dash frame out the vehicle.
I doubt there is anything wrong with the starter relay from what you've described.
But all damaged wires will need to be replaced.

 

[hunt2elk]

There should only be 1 black wire on your ammeter. That extra one would be the very first thing I would be looking into.

 

[Stumper]

Thanks for clearing the questions Don. Hunt2, I want to try and see where that other line goes myself. I did note that in the electrical diagram that the one black line seemed to run to a junction of several other wires, one of which goes to the ignition. I’m wondering if someone simply ran one line that was supposed be in the junction straight to the amp meter terminal. Again though it was like that before and worked fine?

 

[PrescottJeff]

The amp gauge is a power in power out gauge. The red is the battery side and the black is pass through power that that powers everything in the car. If you accidentally put a black ground wire with the black power wire that would cause your problem

 

[Stumper]

Tested - or tried to test continuity of the amp gage today. With the panel laying on my lap I tested between each post and the dash frame and got no continuity OL. I tested the same on the old dash and got the same results!
But the amp meter on the old dash was working??
Both gages showed continuity between the two posts..
I’m lost!

 

[Sixpactogo]

I agree you have created a dead short somewhere. As for two black wires on the ammeter, My car has two wires there also. The second wire is an 18 gauge wire feeding the clock. Other than that, I see no reason to have more than one black wire terminated there.

 

[Stumper]

Can someone help me understand what I’m looking at here. On the wiring diagram- R6 is heavy black to the bulkhead. R6A is heavy black to the amp meter. Q3 is red/wh stripe to fuse box and J1 is red to Batt on ignition switch. L1 is black to headlight switch.


Is this showing a junction of all of these connections?? The second black wire that was on my amp meter is a junction of headlight, fuse box and ignition wires.?? If I’m understanding correctly the second black wire should be ok like this?