Radio cuts in and out while engine is running

[runnergeorge]

Hey guys! I have a 75 c10 Cheyenne with 350/350 LWB. When I bought the truck the previous owner installed a kenwood radio in it and it worked great. Recently, I installed a new distributor and now it seems there is some sort of interference in the radio. I checked the grounds and the power and even redid the connections. The issue only happens when the engine is running. It sounds like a skipping record, no rhyme or rhythm to the skips though. Could it be some sort of interference from the distributor? Any help would be great! Thanks!

[JohnnyPopper]

It  doesn't sound like interference, no whining, or buzz.

Sound like power interruption, Does the front display flicker?

Look for a loose power or ground wire.

[bd]

It  doesn't sound like interference, no whining, or buzz.

Sound like power interruption, Does the front display flicker?

Look for a loose power or ground wire.

This ^^^^^.  Or an "intermittently severed" power/ground wire.  Don't neglect the cabin firewall ground wire to the back of the right cylinder head and the engine-to-battery negative ground cable connections.  Less likely, it could also be a loose connection inside of the radio.

[runnergeorge]

The dash lights don’t flicker at all. The radio also only does this when the engine is running. My first stop was ground, the previous owner grounded it directly to the battery. On top of that the radio requires another ground to be made from the metal radio housing to the metal dash. To check ground I disconnected the battery ground and made a chassis ground, still cuts in and out. Next stop was the power, the radio has two power lines and both are connected to the fuse block. To check this I moved the connections to different circuits on the fuse block, changed the female connectors for new ones and placed dielectric grease on the pins. Still nothing. I will definitely check the grounds around the cabin and engine compartment.

[JohnnyPopper]

Sorry, didn't mean to imply 'dash lights'.

Does the radio have a digital display? Does it flicker when the sound cuts out? 

[dusterdude]

If I may hijack a bit,my 85 has a popping sound thru the speakers although the power lite on the radio stays on.can I assume that may be a loose ground? Thanks

Sent from my LM-X420 using Tapatalk

[SilverMiner]

It  doesn't sound like interference, no whining, or buzz.

Sound like power interruption, Does the front display flicker?

Look for a loose power or ground wire.

I think JohnnyPopper is on the right track here. The OP mentioned installing a new distributor, but I'm thinking it may be incidental unless the new distributor sucks power more efficiently than the old one did. Intermittent and irregular loss suggests to me either insufficient gauge wire to the stereo or weak ground (could also be small gauge). Either one or possibly both can't sustain the watts demanded by the head unit or amp. Be thankful more modern stereos just shut themselves down rather than grenade themselves when this happens.

The stereo is trying its best to keep up but just isn't being fed what it needs. Another remote possibility is that the alternator just isn't keeping up with the demands of the system either due to age or weak wiring. Everything seemed fine previous to the new distributor, so I can only guess the new parts highlighted weak wiring.

Electrical diagnostics via the Internet is hardly a science, but we try anyway.

[runnergeorge]

I see what you mean, no the stereo lights don’t flash that I can see. I performed a test with the ground with the truck running by manually connecting and disconnecting the stereo ground. and I noticed every time I disconnected the ground, the unit shut off (naturally). However, my issue isn’t the unit powering off intermittently, it’s the sound cutting in and out intermittently while the unit is still powered on. I’m thinking something inside of the unit is loose. Thank you all for the great inputs, I know it’s difficult to solve electron issues over the internet.