ettev

The following applies to my 1970 350 cpe:

The fusible link near my horn relay keeps blowing out, and sometimes at the most inopportune of times. According to the Chevy Chassis Service Manual, "A 16 gauge black fusible link is located at the horn relay to protect all unfused wiring of 12 gauge or larger. It is a serviceable piece with an in-line connector and is not integral with the wiring harness".

I've installed an in-line bayonet style fuse holder in this location in lieu of the fusible link. I'm using a 20 amp self-resetting circuit breaker in the holder.

My question is this.......according to the above description of the fusible link in question, am I safe to assume that any device being feed thru the fuse block (clock/lighter/courtesy, tail lamps, stop/hazard, instrument lamps, gauges, directional signals, radio, wiper, heater) most likely IS NOT the cause for the frequent tripping of this breaker. I have to believe that the smaller fuse would blow long before the circuit breaker trips. This circuit breaker is in the 12 gauge line being feed from the main lug on the starter solenoid. Could a shorted out battery cell cause this c/b to trip on occasion? When this thing trips, the car immediately dies. Just like someone turned off the ignition switch. Headlights and starter circuits are non-functional. The interior lights and the radio still work while the circuit breaker is tripped, but not the bigger items. The wire that this fuse holder/circuit breaker is in gets extremely hot, as naturally does the circuit breaker. After a few minutes of cool-down, the car runs again. Open circuit someplace, or a short to ground?

One other curiosity question. While trying to track down my first problem I discovered something strange. The main headlight switch in the dash never did dim the interior lights correctly. I understand that this potentiometer may be dirty, thus not allowing proper contact on the coil pickup within the switch. But, when reading voltage across the small instrument lamp fuse AND the "LPS" tap on the fuse block I get 12 volts with the dimmer all the way in the high position, When I try to dim the dash lights I immediately get zero volts at these two locations and the dash lights go out. Is this normal? I can't imagine that the voltage reading should change at the fuse locations. The switch is what controls all that, correct?

Electrical problems.................they're the absolute worst thing to fix on a car.


[Modified by ettev, 3:11 PM 8/19/2003]

lyonsh

Ain't it the truth. You have a short somewhere in the system. It's located after the fuse/circuit breaker, with "after" being defined as downstream from the power (hot) feed.

Put another way, your circuit goes from power to fuse, then fuse to ground. Your problem is between fuze and ground. If it were between power and fuse, you wouldn't get enough power to blow the fuse/trip the breaker.

Finding where that short is can be a real bee-atch. Single circuits are simple. But engineers like to bundle the wires together, and run multiple parallel circuits from the same junctions. That makes it a royal pain to find out exactly where the short is.

You can buy something called a short-finder that is basically a circuit breaker and an inductive guage. You put the breaker in the circuit where the fuse was, and move the guage along the path from fuse/breaker to ground (of course you usually have to have a wiring diagram/component locator to figure this part out). When the breaker trips, the needle on the guage will jump. As you move the gauge along the circuit, eventually the needle will quit jumping. The short is between the no-jump point and the last point where it did jump. That at least gets you close.

Good luck. Just remember that electron are azzholes: they're small, they're shifty, they're always negative, and you just can't trust the little bastiches. :crazy:

ettev

Just a bump up to the top.

SnoDrgn

Without a schematic this is about all the advice I'd have to offer as well. :leaving:

Big Fish

The wire that this fuse holder/circuit breaker is in gets extremely hot, as naturally does the circuit breaker. After a few minutes of cool-down, the car runs again. Open circuit someplace, or a short to ground?

You certainly have a short to ground or a burned out component on this circuit breaker circuit. The breaker is most likely shutting everything off until it cools, then turns back on. A fuse link is a one-time device that won't reset. Once you find your actual drain of power I would suggest re-installing a properly sized fuse link for safety. Circuit breakers are more likely to be unsafe, especially after a number of activations.

theandies

Looks like you have a few suggestions for your first problem. As far as your headlamp switch is concerned there is a wire wound rheostat that controls the dimming of your dash lights. I appears that the wire has worn so much that it has broken. I have the same problem with mine but I can dim my dash lights a little because the wire is broken almost in the middle of the sliders travel. I just live with it but you can get a new switch if you want.
Good luck

vettemack

My 69 manual states, "A 16 gauge black fusible link is located at horn relay to protect all unfused wiring of 12 gauge or larger". So, my opinion is your correct in your thinking.
The next step would be to look at what is this 12 gauge circuit supplying. There should be two other fusible links at the horn relay. One for the altenator and one for the ampmeter. Since they are a 20 gauge and they are not blowing, I would rule out these two items.
Looking at my manual, one if these lines (12R) comes off the horn relay and goes directly (UNFUSED) to the LIGHT SWITCH, and what else are you having problems with. So based on your statements, my humble opinion would be to check the light switch or replace it.
Good luck,