Hi, I'm hoping someone can help point me in the right direction as I have been racking my brain for the last week. Background: while troubleshooting the stock radio, I had to remove a set of summit gauges including an ammeter. Upon reinstalling, when I attached the two wires to the ammeter posts, the shielding on the water temp gauge began to melt.

Clearly something was shorted although i'm still not entirely sure how/why (I guess its possible I accidentally grounded it to the gauge cluster but i'm unsure). I left the ammeter disconnected and attempted to start the car. Upon attempting to start I found no power to anything (lights, ignition, etc.) I was nervous to reconnect the ammeter so I began testing and here is what I found.

The positive lead to the ammeter was fed directly from the pos terminal of the battery. The negative lead ran back to the positive junction block on the front passenger side of the car next to the battery. I have learned through wiring diagrams that this is what supplies the horn relay and subsequently all circuits with power. I tested all fuseable links and found no issues. What caused me concern is that when I checked that lead that comes from the ammeters negative post, it showed continuity to all grounds i checked inside the car meaning that there is a short.

Whats odd is that if I checked it against grounds anywhere in the engine compartment, including the engine block, it did not show continuity (short). I've disconnected the fuse block from the junction block on the firewall in order to isolate the interior wiring from the engine compartment. Before doing that and still now after, checking the BATT terminal of the fuse block against any ground under the dash or on the door jam shows a short. There is no sign of any damaged or burned wires with the exception of that lone temperature sensor wire which is routed by itself.

Any ideas of where to go from here in trying to find out where a short might be and why the grounds might test differently between the interior and engine compartment? Thanks in advance.

 

Without the ammeter in the equation...power went from the battery, to the junction block, across the radiator core support, to the horn relay (another junction). Then one of the hot wires from the relay goes to the bulkhead connector on the firewall to feed the inside of the car. You disconnected the ammeter, which was in essence a bypass route from the battery to the junction block. But, I don't see where you connected those two ammeter wires together to power the junction block back up. I don't like using ammeters, your "cooking" and a possible fire being one reason. A volt meter is my preference.

 

Exactly why I ditched my Ammeter and dropped $100 on the Voltmeter to go in my console. I hate to hear youre having this problem. but problems like this have been known to start a fire or two and trust me you dont want that. So, on the bright side, you are just looking for a fix instead of rebuilding your car. when u figure it out be sure to let us know what it was. I just rewired my entire car and I always appreciate good info for future reference. Good Luck man, hope you get it figured out soon.

 

Thanks, I actually forgot to mention that. You are correct, I didn't reconnect the two ammeter wires which in turn left the entire car without power. The reason I didn't was because I was afraid it had a dead short somewhere and that would fry the car. The reason I thought that (and please correct me if my logic is bad) is that when I use a DMM to check from the lead that goes to the front junction block to a ground in the car, I get "continuity". My DMM has a setting where it is set for 200 Ohms or less and will beep which helps determine if you have an electrical pathway. Since that main power lead was beeping when I also touched a ground I assumed that meant it had to be shorted. I'm wondering if that's not the case.

Also, is there a way I could reconnect the main lead without worry of it being shorted? How would I know (other than the car catching on fire)?

 

From your description, it would appear your short was created at the gauges, not under the hood. Pull the battery wire that ran to the amp gauge, and connect it to the junction block. But before bolting it down, try touching it to the connector first. You'll get an initial spark, but if you have a short, you'll see fireworks! Our wiring systems are not all that complicated.

 

When you say you have continuity from hot to ground you could be getting it from something as simple as having the door open to where it will show continuity from the dome light. I would pull all the fuses and check individual circuits. I would feed the positive terminal block directly from the battery and eliminate the ammeter all together. Also get yourself a detailed wiring diagram and check every wire as a last resort but chances are pretty good that the problem lies where you were working on the radio.

 

How would you know HA HA.

 

Thanks everyone. I did confirm that the testing I was doing to assume there was still a short was flawed. I was using a test light and a meter to check circuits but had two issues. First I had not pulled all of the fuses so where I had continuity to ground on the positive side of one circuit, it bled over to other circuits.

Once I had pulled all of the fuses, the apparent short was isolated to the lighting circuit which as JustinA pointed out will show continuity to ground right through the light bulbs. So after all that, I eliminated the ammeter wiring and went straight to the junction in the front of the car, put everything back together and seems to be good to go.

Bright side is I learned a ton about the electrical system in the car! Thanks again for the help.

 

I'm no fan of after market ammeters either, after losing a 1970 AMX to a bad one.