Electrical Problem (Radio)

[TheSeeker]

Hello all.. I am going to try and explain this as calm and clear as I can, I apologize in advance if its not, because im as angry as a spotted ape at the moment..

I have had a basic stereo installed in my truck for the better part of a year and a half now. I installed it myself, and followed the instructions for wiring, used solder and heat shrink etc. Nice clean install. The REST of the wiring behind the dash is another story, its a nightmare to trace anything back where it goes.

Anyway, 3 days ago, I installed a pertronix ignitor to get rid of my points. I again, followed the easy as pie directions and got rid of the resistor wire, installed a fresh 12 ga wire to power the unit, tucked it away, nice and clean. Cleaned all connections to alt, battery, etc. Everything was perfect. Truck ran great and for the first time in 11 months, I didnt have an urgent repair to get to at all.

Flash forward to saturday night, Now my radio, which has been working fine for a year, is giving me fits. To explain better, whenever I press the brake pedal (lights come on) the radio cuts power. It loses power for 2 seconds, and comes back on. If I turn on the headlight switch, which I did to get home after the local cruise, the radio died completly. Will not turn back on. I got home and parked it.

Sunday I went out and retraced my steps. Starting with the radio ground. It is clean, and connected. Second I checked my pertronix wiring. Even unplugged it. Same problem.

I am not sure where to begin now. Is it a battery? (it is 4 years old but never given issues) Is it the headlight switch? Is it a ground somewhere? Is it just a lost cause and I should remove the radio and wiring and throw in the the damn trash and weld the hole and pretend I dont know what music is? I am frustrated beyond belief and HATE wiring problems. I am pleading for your Gurus knoweldge. Please, someone tell me they have an idea!

Thanks guys

[ChevLoRay]

You said the wiring behind the dash is "another story". You didn't say what year model your truck is, but that just means that these trucks are from 40-45 years old. The wiring is as old as the truck. Check out www.wiringharness.com for replacement harnesses. I got mine through Wes at Classic Heartbeat, for a bit less than what the website has 'em priced.

I'm sure your original wiring insulation is brittle.


Your description sounds like your radio is grounding thru another component...or another is grounding thru your radio. Electricity takes the path of least resistance, just like water.

It sounds cheesy to say so, but my bet is that a new harness would be very helpful to you.

[TheSeeker]

I am sure a new harness would at least give me a clean slate. Problem is, I cant afford that right now, 350 bucks for a dash harness is a bit steep for me

[davepl]

I would guess a bad ground. The brakes are also a switched ground, which makes me suspicous.

The radio should only have three connections that interest you: switched power, battery power, and ground. You should run EACH of these far enough to a point that you KNOW and are CONFIDENT is good. Don't tie into the rat's nest of previous owner wiring mess.

Don't run your ground to something else under the dash (except the firewall I suppose). Don't tie your power into something just happens to be orange so is probably power...

Until and unless you replace the harness and know that everything is right, you're going to have to treat any existing wiring as suspect.

But, like I said, it's an easy fix, because there are only three wires. Run them to the fuse box at a minimum.

[TheSeeker]

Should I be worried about the headlight switch or battery or anything else? I guess the easiest thing to do now, is to drink a few beers tonight, then go out tomorrow after work and remove the stereo and trace back all my wires.. Start from square one. Does anyone have any suggestions what to use for a ground behind the dash then? Im not sure where to run it.

[TheSeeker]

To clarify, I have it bolted to a metal bracket right now. I beleive it was where the original speaker was under the dash

[AirSpeed]

Have you checked the positive connection where it hooks into the fuse panel? It may have a very weak connection and when power was sucked up by the surge of the lights going on it may have taken away enough to shut down the stereo. Try cleaning the connection and the fuse itself.
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[davepl]

Originally Posted by TheSeeker

To clarify, I have it bolted to a metal bracket right now. I beleive it was where the original speaker was under the dash

I would use either the firewall itself or part of the reinforcing structure of the dash (if you've stripped one of these down, then I'm speaking of the part that's bolted in and cannot be removed). I've seen a lot of underdash stuff grounded to the heater box. It's painted, has plastic pieces, and is often insulated from the firewall by gaskets and sealant. Might be a good ground if it makes contact somewhere, might not. Improve your odds by using what you KNOW must be a good ground.

Going to a bracket -might- work, but then it depends on how well that bracket is grounded and how much paint is on whatever that bracket in turn mounts to, all the way to the frame and battery.

Some things, like fuel injection ECUs and capacitive discharge ignitions, need to often go right to the battery post.

The mention above about voltage drop when you turn on the headlights is part of the reason. Imagine you've got a sketchy power or ground connection and then you hit the brakes or turn on the headlights. If you can't get enough current to flow you're going to have a voltage "brownout".

This is just a radio, but if its a modern one it just might not be tolerant of low voltage (you could see if its worse when the engine isn't running, which would be a clue).

[TheSeeker]

Ok so I checked some more things, Im going to make a new clean ground on an area you suggested. I checked the other grounds on the truck using a diagram I found on the site. Everything appears to be ok there. The radio does seem to act up more WITHOUT the engine running, as opposed to while driving. Just when listening on acc or on position does it consistentily die. The headlight switch being pulled instantly kills it no matter if engine is running or not though.

[cdowns]

if you looked at all the grounds you have effectivly done NOTHING that only works if you have xray vision// only way to check grounds is to remove clean and reinstall

[TheSeeker]

By checked the grounds, I meant I cleaned the contact points and re bolted the straps in. Sorry I didnt make that clear. Also, this morning during my ride to work (the truck is my DD) I had no ISSUES... I pulled out my headlight switch and everything stayed on.. except my dome light doesnt work now.. hahaha I cant figure this out!

[davepl]

Another important point is that when you are testing grounds and so forth you're not doing so under load.

I see this all the time in the "Q&A" sections of magazines: they tell you check for a voltage drop, like between the battery and the headlight switch for example. When there's no load, you'll get full voltage no matter what, because your meter is drawing some tiny fraction of a milliamp or whatever. It's when the circuit is -loaded- that you need to measure a voltage drop.

As an example, let's say you had too small of a wire powering your starter. You've got 13V at the battery. You measure 13V at the starter. No problem right? But when you measure it during cranking, maybe there's only 11V, and that reveals the problem.

Same deal for grounds.

Now, if you had the meter on your potential ground spot and then invoked all the other loads you were worried about interfering with the radio (brake lights, headlights, wipers, heater, etc) and confirmed there was never a drop, then you'd be OK. But that's hard to do accurately.

[TheSeeker]

Ah I see.. you guys are awesome.. Ive got more things to check when I get home.. I cant afford a new harness right now, saving pennies for one, but until then I will do what I can to trace wires where they go, clean them up and label them. Only way im going to find out where the problem is now seems to be slowly checking everything one by one.

I do have a question though, it seems that when it is warm outside, I have fewer electrical issues, as opposed to before sunrise in the AM. Is this my imagination, or could this be a clue to start somewhere as well?

As always, you learn something new everyday. Thanks for all the help so far guys

[blackdawn]

when its cold everything shrinks, so its more than likely a connection somewhere. i know you have been checking the ground on the radio, but have you also checked the cab ground to the frame, and the grounds to the engine/ bat. those are all important as well

[AirSpeed]

One way to figure out if its a simple connection issue is to simply direct wire the pos to a hot connection on the fuse panel and make a temp direct ground. Your stereo has more than one ground, the wired ground, the antennae and the ground it makes through it being mounted to a steel dash. I would try connecting the positive to a new lug and see if that helps. Is it a stereo with a mechanical switch or one with a soft touch button with a built in relay?
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[davepl]

Originally Posted by AirSpeed

One way to figure out if its a simple connection issue is to simply direct wire the pos to a hot connection on the fuse panel and make a temp direct ground. Your stereo has more than one ground, the wired ground, the antennae and the ground it makes through it being mounted to a steel dash. I would try connecting the positive to a new lug and see if that helps. Is it a stereo with a mechanical switch or one with a soft touch button with a built in relay?
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Good point. For the cost of ten feet of cheap speaker wire you could even temporarily run it right to the battery posts. That'd tell you if its an electrical integrity problem or something more complicated.