Hot Rods need help with electrical short

I recently (6 months ago) installed a Painless wiring harness in my '55 Chevy. It has been working fine, started it up the other day turned on the lights blew the hazard fuse. It has bright lights but no dim headlights or tail lights. The brake lights work and the turn lights work. Using a multimeter and the negative battery cable unhooked, the dim headlight circuit has continuity to ground, checked the switch it is good, floor dimmer switch is good. With the negative cable off the battery the wire (928) which feeds power to the light switch has continuity to ground. I believe this is the short. Any ideas?
Thanks,
the coupeman36

 

Are your front park light/indicators using a dual filament bulb in the one socket?
If indicators are switching positive, and headlight circuit is switching earth, you can get a short if a dummy puts a single filament globe in that spot.
Otherwise remove indicator bulbs, turn on the lights.
If the short disappears, put the bulbs back in, one by one... with the lights still turned on.

I'd start there.

 

When you say "continuity", you need to remember that a headlight circuit will show up as a very low resistance. A 48 watt bulb will draw 4 amps at 12 volts, and have a resistance of 3 ohms. When you are checking for shorts in a circuit, you must "zero" your meter (short your probes together) and then subtract this resistance from your measured figure . This "lead resistance" may be as much as 0.8 ohm. The easiest place to start this faultfinding would be to unplug your dimmer switch, and check for voltage at the "common " terminal ) with your lights "on", but headlights unplugged. Then you can short out the low beam circuit with a jumper wire at the dimmer switch . If this goes well so far, then plug in one headlight at a time. I have had dimmer switches short internally to ground, you can also prove this by unscrewing your dimmer switch (thereby it loses its ground) and see if your fuse blows then.

 

Lets see, you have high beam headlights but no low beam, no taillights, and you blew the 'hazard fuse' so I assume you have four way flashers. Brake/turn lights work. Each of these (headlights, taillights, turn, brake, and hazard) should be separate unrelated circuits with individual fuses or circuit breakers, so blowing one fuse should have no effect on any of the others if in fact they are separate circuits. A few other questions... Does your headlight circuit contain any relays? If you've lost power to the dimmer switch, that may explain the high beams working if they're fed through a relay. Are these separate circuits, or is there common feeds to any of these? They may share a common wire though; possibly the grounds. An overloaded ground wire could have shorted to your hazard circuit. If the 'main power' wire to your light switch reads to ground with both ends disconnected, yes there's a short in it.

 

To troubleshoot I put a lightbulb in series with the ground cable and the battery. That adds resistance to the circuit so it won't blow a fuse, the bulb will glow dim. keep disconnecting things until the bulb goes out and theres the problem.

 

A multimeter won't give you an answer. Use a test light.
You haven't recently installed a radio, have you? Some people mistake the radio earth for the instrument illumination circuit.