ok, i'm a nuts and bolts kinda guy so this elec. problem has almost got me whipped... i pulled the dash apart to change the oil guage and cleaned the ameter contacts while i was there. when i put it back together the interior lights stayed on until i played with with light swtch. next day, no battery. i tried to jump it and actually melted the posi jumper cable. now i figure i got a hot wire grounded somewhere but how do i track it down...all fuses are good and i,ve taken dash back apart but don't see a wire charred or anything. bought a multi tester but not really sure how to use it, i'm nuts and bolts remember... can any of you experts help this poor old guy get his 71 BB back on the road. its getting warm and i'm chompin at the bit...

 

i feel your pain on taking that dash out & in , I had an elec prob on mine but I was blowing fuses and was able to at least pt myself in the right direction , but the only way i was able to find it was in the dark , in my garage , in the resto I had zip tied the trn sig flasher to a metal bracket and it was sparking everytime it blew the fuse. Maybe someone with some real elec knowledge will pipe in

 

What did you do to the light switch to get the interior lights to go off? Did you only pull the center section of the dash? First guess would be a pinched or frayed wire in the dash harness somewhere. It could be something back in the harness that shorted when you manipulated the harness.

First disconnect both the negative then positive terminals on the battery. Use the multimeter to measure resistance from one cable to the other. It should read 8.8.8.8.8 or O.L or some number of M Ohms. Your problem will probably yield some low resistance.

Now disconnect the ammeter and measure across the cables again. This will rule out the ammeter that you messed with. While you are in there do a good detailed visual inspection of all the wiring behind the center dash looking for cracked insulation or exposed wire.

Next disconnect the forward lamp harness/ engine harness from the fuse panel in the engine bay and measure again this time measure from the large contact in the connector on the firewall. If you get a low resistance here then reconnect the harness. This will rule out all the wiring forward of the firewall.

Next disconnect the rear lamp harness and measure at the battery cables again. I know, I know it shouldn't be back there, but we need to isolate the fault to a particular harness.

If you are still getting bad readings, pull fuses one at a time then measure again at the battery cables. This will help to localize it to a particular circuit.

Let us know how that goes.

 

I am going to guess that one of the terminals that you reinstalled is touching ground. The problem is possibly on the ammeter. Most terminals have a plastic piece or plastic washers that prevent the metal stuff from touching the housing. I am going to suspect that one of them on your ammeter terminals is cracked or overtightened to the point where it is slightly touching. If for any reason, it slightly touches, it will cause some bulbs in the interior to light up. And this could cause a slow discharge of the battery. Whenever you remove a terminal, be sure to check to make sure that the terminals and posts do not touch on the surrounding metal areas. The plastic insulators get brittle with age and are prone to cracking.

Also, take an ammeter and recheck all of your circuits. One way to check to see if the short is in a particular circuit is to remove that particular fuse and leave the car sitting overnight. If the car discharges the battery, you found the problem. If not, continue to remove and isolate the others until you find it. This only works for fused circuits though. The reason for a circuit having a short and not blowing the fuse is that sometimes the fuse is slightly larger than the power draw from the short. I once used 5 amp fuses in all the circuits and found the short. One fuse blew and indicated that there was a draw in the wiring for that particular circuit. Make sure not to turn on any electrical devices or lights when testing with the 5 amp fuse though. Or else you will get a false indication of a problem.

But before I get blasted for my backyard troubleshooting techniques, I must add that the proper way is to use a multimeter and test each circuit. That method takes a little more understanding of the principles of automotive electrical circuits.

Good luck!

 

Sharky Guam also has a good idea. Using low rated fuses might show where the short is. If the 5 amp ones don't work. Try 1 amp fuses.

Also, I edited my above post to be more accurate. Once you disconnect the forward lamp harness, you disconnect the battery from some of the circuits up there.

 

ok LS1, thanks for the help, i did all that you said and the ohm reading stayed constant on every circuit... let me know if something else comes to mind i can check. in the meantime i'll try sharky's idea and get some 1 amp fuses and see if anything shorts. i also noticed i been bubba'd, my clock doesn't have a connection on it and i went to my AIM and saw the orange line that should be connected to the clock attached the hot lead on the radio...something else to do but i'm getting quite proficient at pulling the dash.....oh well...neverending but i love the challenge...thanks guys for all your input

 

What were you getting for a reading?

 

Go back to your ammeter and carefully look at it the grommets, connectors, and wires.........I suspect that the problem is there......

There is another way if the short is enough to make a circuit wire hot....get an infrared thermometer used to find hotspots. Connect all the wiring and use the gun to find the wire that is getting hot......that should point you to the short.....

 

ok guys, i replaced all the fuses with 2 amp ones yesterday... checked them this morning and alas, none were blown... i have a .2 reading on the ohm meter. stays at that reading and never changes....so where do i go from here... i'll check the ammeter connections again and see what i see...

 

.2 would indicate a short to ground on the main power circuit. Now with the forward lamp harness disconnected, pretty much the only thing still hooked up would be the starter, alternator and go figure the ammeter. Try disconnecting the ammeter and taking the reading again.

 

\ok i disconnected the front harness and the ammeter and checked at the battery and still got the same .2 reading. now do i go to the starter and the alternator and check across those poles or what... i'm still determined to figure this out... with your help and patience of course...

 

Leave the front harness disconnected. Go to the starter and there should be 2 wires on the terminal where the battery cable connects ( the battery cable and a 10 gauge wire.) Disconnect both of these and measure at the battery cables again.

If you are still getting a .2 reading, then your battery cable is grounded.

If you get a high resistance then check between the terminal of the starter and ground. If you get a high here, then your starter is good and reconnect both leads.

Next would be to go to the alternator and disconnect all 4 wires. There should be a plug with 2 and then 2 others. Measure between each of the wires and ground. One of them should be low (that is good) and the other 3 should be high resistance.

Once you do that let me know what you come up with.