Did you smell anything when this was going on? Any smoke?
Isolate the part of the car that has the short. If you were working on the dash start there...Disconnect & Isolate....Something might being grounding out within the dash...Which are the blown
fuse? track down their application..A poor instrument panel ground can cause voltage limiter problem....
if you have the body harness disconnected and you still blow fuses, the problem is under the dash or the door/dome light switches. With the harness disconnected and no blown fuses, pull the interior and follow the wires till a problem area shows up.
Trouble Shooting Book.......
If a circuit is overloaded, meaning beyond the preset amount of amps labeled on the
fuse, the fuse blows (or opens the circuit) to protect the wires from breaking down and burning. To cure this problem, lighten the electrical load on the circuit by removing things connected to the circuit until the fuse holds.
An electrical short can be from the hot wire to ground or a hot wire to neutral. In either case, the fuse will open and shut the circuit off. To find this problem is a little more complicated, but start with the easiest solutions and work backwards to the
fuseconnection. Start by finding the affected circuit that is off and what is connected to it.
The 15-amp fuse protects #14 or larger wire, the 20-amp fuse protects #12 or larger wire, and the 30-amp fuse protects #10 or larger wire.
Finding an electrical short can be one of the most frustrating and time consuming problems in owning an antique vehicle (or any vehicle for that matter). But where do you start to isolate the cause of the problem?
Here's the scenario: Everyday or two you have to jump start your car because the
battery has drained down to the point where the car won't start.
As with all scenarios, we have to make some assumptions. We have to assume that your battery is good and was fully charged, that your charging system is good, that you are not blowing fuses or fusible links, that you did not leave any lights on (interior, glove box, under-hood, etc.) and that you did not leave your car's
ignition in the "run" position with the engine off. If all these were checked, you probably have something that is drawing enough power to drain the battery (short?), but not sufficient enough to blow a
fuse or fusible link in a protected circuit.
Let's try to locate the possible short. If you have a test light (easily obtained at any auto part's store) disconnect the negative
battery cable from the battery. Connect the lead from your test light to the negative battery cable and connect the other end of your test light to the negative battery post. An assistant or 2 small hose clamps will help hold your test light in place. (An ammeter (not a voltmeter) will be a more accurate substitute for a test light assuming you can read an ammeter. Normal constant draw on the battery is about 200ma.)
On your test light, you may get:
1.) No light. This means no power draw (no problem) or a bad connection on your test light (fix & re-try).
2.) A quick flash of the light, then nothing. This may be normal as the capacitors in the electronics charge up.
3.) Constant light. This is probably what most people will see. Whether you have a problem or not. Small devices like clocks, radio displays, etc. will constantly draw a SMALL amount of power and cause the test light to dimly glow. This is normal. If your test light glows very bright, you have a problem with something drawing too much current.
Keep the car doors closed (or the door jamb switches depressed) and remove the under-hood light bulb.
First, disconnect all wiring to the
alternator(the main cable and one/two plugs). If the test light glows dim or is off completely, you've found a problem. There's an internal fault in the alternator. This can happen even if the system is charging the battery. Have your local auto parts store bench test your alternator and repair or replace if necessary.
If your test light still glows bright, start by pulling each
fuse, one at a time. With each fuse pulled, watch the test light. If it goes dim or off, you've probably isolated the harness (engine harness, dash harness, forward lamp harness, etc.) causing the problem. If the test light still glows bright, re-insert the fuse and remove the next fuseand watch the status of the test light. If after removing all the fuses, your test light still glows bright, then disconnect each
fusible link, one at a time. NOTE: If you think you've found the harness or circuit causing the problem, it is wise to complete the test and remove every fuse, one at a time, noting the test light status. It can be a compound problem spanning multiple harnesses.
Once the specific harness is isolated, you now need to locate the specific circuit within that harness causing the problem. Find out what the involved fuse(s) are for and trace it from there. A wiring diagram is extremely helpful here, but common sense can find many problems without a diagram. The most likely culprits are bad switches to the interior lights (to include the trunk & glove compartment.
