1973 - 1979 F-100 & Larger F-Series TrucksDiscuss the Dentsides Ford Truck
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I replaced the wiring in my 77 ford explorer with wiring and guages from a 75 custom. No problems there. I added an inexpensive aftermarket cassette stereo and there is some noise when the engine is running. There is a bullet shaped tube with one wire mounted near the voltage regulater that I always thought was a radio suppressor. I tried replacing this with no change. Someone just told me it was to protect the alternator and had nothing to do with the radio. Did the original radios have a suppressor built in to them? I hooked the power to a yellow accessory 3 hole plug behind the guages. I wonder if I have to tie it into the original radio power supply in order for the suppressor to work correctly. Someone suggested buying an after market suppressor from Radio Shack, but they have never heard of it.
The "bullet shaped tube" is a capacitor and it is for radio supression.
Your shouldn't have to tie into the original wiring.
The first thing I would check would be the plug wires. They are the number one cause of radio noise. If they're old or cracked replace them with a QUALITY set.
The next source of noise is usually the alternator. You can get a choke/filter at most audio stores that gets wired into the radio wiring to help filter out the interference.
What does the sound sound like? If it's a lower pitch sound that varies with the engine rpm then the interference is from the trucks ignition system.
If the sound is high pitched it is from the alternator.
I remember buying a choke/filter at Radio Shack several years ago (1980-81), I remember it was $25 at the time(pricey), but it worked real nice. It was tied into the power supply to the radio. I had the Molly Hatchet crankin then! Flirtin With Disaster, or some Gator Country, a little bit of that chomp, chomp!!
Try tying your coil wire in a loose knot, sometimes this helps.
This can actually make things worse. Making loops out of switched signals causes inductive coupling that can cause interference.
The guys are right; the "bullet shaped tube" is a radio supression capacitor. It acts as a low-pass filter, to remove ignition noise out of the audio band. I think these capacitors are electrolytic, which means the dielectric can dry up over time at which point they must be replaced. Sometimes, even with a radio supression filter, you can still get noise. If this is still the case, try looming your plug wires differently, or running shorter wires if possible.
Ignition noise was much more of a problem in the early days. The original AM decks had very little in the way of input filtering, so a large bulk capacitor or series choke on the radio power supply was necessary to filter out noise from the plugs firing. Modern head units typically don't have as many problems, but it's not unheard of.
I replaced the radio suppressor with one from a parts truck. No difference, but they both could be bad. The stereo I installed is a very simple dial radio w/ cassette deck. Not expensive at all.
I will have to listen to the noise, not sure if it's high or low.
Thanks for straightening me out. Maybe I should pull the supressor out of my 69 mustang and see if that makes a difference as I get no interference there. It's a much better stereo than in my truck.
Everything is working, but last night I "bumped" the radiator with a wrench and now have a leak in it. If it's not onething, it's another with old trucks.
i vote bad ground wire. also do any of your speaker wires run directly in line with any power wire tide to or in a wire loom that will make the noise too. but i bet you just have a lose or bad ground wire. imo
If you did it wrong and no one tells you is it right?
Randy (AKA Skinny)
Frankenweenie is a 1972/67/69/76/78 FORD F-100 4x4 all in one!!
Taco is a 1992 Toyota truck w/ the 22RE motor tuned up.
The Regency is a 2004 Regency RST w/ a LS1 and some other goodies.
He hood has the ground strap and the metal bracket from the radio to the bottom of the dash is the ground for the radio. I will run a separate ground off the back and see what that does. All good ideas. Thanks again.
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