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Old 01-06-2010, 07:08 PM
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Complete Rookie Electrical Q

To me, electricity might as well be magic, so what would cause the following issue...

About a minute or two after I turn on the head lights, I loose them, the parking lights, the brakes, the interior lights, and the radio. After the truck (1990 Chevy) is parked for a few hours, everything comes back like magic. This happens every time like clockwork. I am thinking a relay.

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Old 01-06-2010, 08:33 PM
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Hmmmmmmm

Hey 454, I'm gonna take a shot in the dark. It sounds like a harness problem, maybe bad and corroded connections in the firewall harness. Disconnect the wiring harness at the firewall(unplug outside from inside) check for corrosion, clean, plug it back together. Go from there, see what happens. It's the first thing I'd check. Maybe check all plug in connections on problem circuits. Then go from there. Oh, its a '90, I'd have to look but, could be a body contol module issue. I don't know if they had one. Food for thought. olnolan
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Old 01-06-2010, 09:25 PM
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COuld be a ground connection issue. When the lights go out, check at the bulb connection for both power and ground. My guess is you have a missing body ground.
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Old 01-07-2010, 06:51 AM
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Yep

T-Bucket is right, Ground issue is more likely.olnolan
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Old 01-07-2010, 08:38 AM
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Another vote for a bad ground.....
Something experience has taught me, with many aggravating lessons, is that anytime you see electrical stuff going on that seems to make absolutely no sense, 98~99% of the time, it's a bad ground,
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Old 01-18-2010, 01:38 PM
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If this happens with engine off and all the electrical fades away (instead of just stopping instantly), it could be a weak battery. After a couple of hours, the battery has recovered and can power accessories again for a bit of time. Does the starter turn properly when cranking?
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Old 01-18-2010, 02:53 PM
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Does this have a headlight relay? If so maybe getting hot.
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Old 01-18-2010, 03:07 PM
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for fire safety:
you have a amps sensitive overload auto-reset relay and/or a thermal overload contact strip in the light switch itself which is tripping....
(to prevent a harness wire fire from to many amps for the wires to safely carry)....

it/they are working correct,,,amps makes heat and with to many amps present it/they are killing the power when hot enough in order to protect the wires insulation...

after so many minutes it/they cool off and make contact again and then the lights work again like magic for a little while till hot again....

since all are dieing at once and all come back on,,,the lights switch itself is a likely cause....
all of those lamps are controlled and powered thru the lights switch which is power direct from the batt....
(the radio is not normally on the lights switch however but possibly a overload relay is on the fuse panel)

what else does or does not work when the lamps go out,,,idiot lights/starter/gauges/etc?

first:
clean the batt neg terminal cable connect,,,and where it is bolted to the motor and make sure there is a ground wire from the batt or motor to the truck body...

sorry I don't know absolute if your lights switch has a thermal breaker but I would then start with testing that if it's not a batt cables problem...

anybody know what/where the lamps safety breaker is located on his truck???

Last edited by red65mustang; 01-18-2010 at 03:30 PM.
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Old 01-18-2010, 04:49 PM
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Quote:
Originally Posted by red65mustang
for fire safety:
you have a amps sensitive overload auto-reset relay and/or a thermal overload contact strip in the light switch itself which is tripping....
(to prevent a harness wire fire from to many amps for the wires to safely carry)....

anybody know what/where the lamps safety breaker is located on his truck???
If it is not on or in the head light switch itself it should be in the main fuse panel (in the circuit that feeds the light switch) if not you may have to find a wiring print for the truck to find it.Most likely this is the problem as Red has stated.
Good Luck!! Post back and let us know what you find .
Kenny
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Old 01-19-2010, 08:14 AM
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correction/clarification:

remove the neg batt cable and clean the batt post and cable end inside,,,at the contact area...

adding just abit?:
just due to age and use all the devices and wiring in the circuits resistance does increase which means more amps (aka heat) needed...
just due to age and use the safety breaker does wear so it pops (normally/typically) at a lower than "when new" amps load rating (printed on the breaker)....
when it's popping at slightly lower amps is a better safer "early warning system alarm" that something needs attention....

it's a fairly common situation in a 20 year old vehicle
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Old 01-19-2010, 12:20 PM
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The only things that go off are the radio, headlights, brake lights, tail lights, and interior light. They all go off all out once and instantly after a few seconds of the headlights being turned on. Everything else works as always. So it's not the battery. I doubt it's the headlight switch itself as that is just a simple aftermarket toggle switch.

The battery cables are brand new and clean as are the battery terminals. The ground goes directly off of the battery to the engine block.

Attached is a picture of the fuse panel. The silver relay on the right gets very hot. The previous owner didn't have it in, and just had used a piece of wire to jump it. Maybe the parts store gave me a relay with too low an amp rating?
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Old 01-19-2010, 12:41 PM
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Quote:
Originally Posted by 454headache
The only things that go off are the radio, headlights, brake lights, tail lights, and interior light. They all go off all out once and instantly after a few seconds of the headlights being turned on. Everything else works as always. So it's not the battery. I doubt it's the headlight switch itself as that is just a simple aftermarket toggle switch.

The battery cables are brand new and clean as are the battery terminals. The ground goes directly off of the battery to the engine block.

Attached is a picture of the fuse panel. The silver relay on the right gets very hot. The previous owner didn't have it in, and just had used a piece of wire to jump it. Maybe the parts store gave me a relay with too low an amp rating?
That "relay" is a circuit breaker. If it's getting hot, chances are it's getting too hot at times, and this is when you lose the lights, etc.

Try removing it to see if the same things quit working as when the lights, etc. go out when you're driving.

If so, that's telling you there's a problem w/that circuit that has to be repaired. Otherwise, you could burn the thing to the ground one day.

If you have a toggle for the headlights- unless it only works a relay- it has to have a rating that exceeds the draw of the lights! Otherwise, it could get hot and cause the circuit breaker to trip. If it's hot wired, it could start a fire, too.

AFA the radio- it should be on an entirely different circuit. But w/the wiring having been "modified", all bets are off as to what's wired where and to what.
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Old 01-19-2010, 01:04 PM
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Quote:
Originally Posted by 454headache
The only things that go off are the radio, headlights, brake lights, tail lights, and interior light. They all go off all out once and instantly after a few seconds of the headlights being turned on. Everything else works as always. So it's not the battery. I doubt it's the headlight switch itself as that is just a simple aftermarket toggle switch.

The battery cables are brand new and clean as are the battery terminals. The ground goes directly off of the battery to the engine block.

Attached is a picture of the fuse panel. The silver relay on the right gets very hot. The previous owner didn't have it in, and just had used a piece of wire to jump it. Maybe the parts store gave me a relay with too low an amp rating?
That appears to be a auto resetting thermal breaker, if too much current is drawn tru it ,the contacts will open cutting power to the circuit that it feeds. If it is getting very hot this could very well be your problem. Pull it from it's socket and turn your light switch to on, if the lights do not come on ,turn the switch to off put the relay back in it's socket and try the light's again .If they come on most likely this relay(?) is your problem......but as has been stated in previous post's in this thread the total resistance in this circuit may be the true culprit and the relay is simply doing what it is supposed to do .I would not wire this circuit in any way that would circumvent the relay or the wiring.You run the risk of something getting too hot and setting your truck on fire. Separate the circuits and trace back tru each one , check the connection's ground paths and the postive side of these circuit's need to be checked to see if they may have a high resistance to ground. this can (and is) a PITA. You will need a wiring schematic of the truck ,a volt /ohm meter and you will have to disconnect both ends of the hot wires to do this. Connect one lead of the meter to the light power carrying wire (disconnected from both ends) and touch the other lead to ground. You should not get a resistance reading.
This is a quick over view of what you need to do to check it out.
Good Luck!!
Kenny
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Old 01-19-2010, 01:26 PM
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Opps sorry bout that Cobalt and I posted just about the same answer. Dang he can type faster than me!! O well
Kenny
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Old 01-19-2010, 02:04 PM
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is it a aftermarket high watts radio or just stock?

as posted,,,yank the breaker out while the lights are on to prove they ARE on that circuit breaker...

if NOT do NOT go forward with this test:

radio OFF, truck off, everything off,,, take the 20amp fuse top left and put that inplace of the circuit breaker and then turn on JUST the parking lights,,,stays lit ok turn on the low beams,,,20amp fuse is barely enough for highbeams but go ahead and turn on the highbeams if the low beams stay on,,,if it pops try the 25amp fuse....

if that pops there is definitely a wiring problem,,,that's more amps than the #12 wire size is supposed to carry...

the radio is normally on it's own fused circuit (on that panel) and I can't see one marked for radio....
good chance,,, that with the now steady on lamps on,,,if you turn on the radio it will pop the fuse immediately....

headlights are always on their own dedicated circuit for safety,,,you don't want a radio problem to cause losing lamps while driving!!!

post back and confirm the breaker is controling the lamps!!!
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