Headlights flicker and radio cuts out when driving over a bump

[PhotonFanatic]

Man, it's like you fix one electrical gremlin, and a new one rears it's ugly head. I recently replaced my starter and fixed some ground wire issues, and now the starter finally works good. But when when the road gets a little bumpy, my radio restarts (modern radio) and my headlights flicker. I was hoping someone here might know what electrical connections those two share.

I wiggled a bunch of wires under the hood, including all the headlight wires. While listening for the radio to cut out. But it never would. The main grounds to the engine and the frame are fine and have recently been cleaned up. Is there anywhere else I should check? Surely the starter wires couldn't have anything to do with the radio and the headlights, right? Especially when the starter works great now. Thanks!

 

[scrap--metal]

I had the same issue in my Monte Carlo years ago. The car would still run solid, but the headlights and radio would cut out over big bumps (scary when driving at night). Replacing the ground strap between the passenger side head and the firewall fixed the issue.

Have you replaced that ground strap or verified that the ends are clean and still secured tightly?

Good luck!

 

[dvdswan]

Loose or corroded ground(s). Also, check for corroded wires to grounds.

You must be registered for see images attach

 

[Ricko1966]

Absolutely the starter wires could cause the problem, and if the problem came after a starter swap that's the first place to look. Inspect your positive cable, and clean, tighten, check all connections at the starter. Ill assume you disconnected the battery, clean, tighten and inspect everything there.

 

[PhotonFanatic]

Loose or corroded ground(s). Also, check for corroded wires to grounds.

If only I knew where they all were. A huge help to this site, would be if someone had an info graphic that showed where all the ground wires are on these trucks. How many are there in total... who knows? Maybe there's 10 or 15. But I'll look for one going from the passenger side head to the firewall. Are you certain the trucks share that in common with the Monte Carlo?

Absolutely the starter wires could cause the problem, and if the problem came after a starter swap that's the first place to look. Inspect your positive cable, and clean, tighten, check all connections at the starter. Ill assume you disconnected the battery, clean, tighten and inspect everything there.

New battery, connections are all clean. I'll recheck the tightness. Looks like I get to drop the starter again. The big power wire to the starter is new. But those other two wires that connect to the solenoid aren't in great shape. I did some minor repairs to them with butt connectors, and I had to cut out a few spots where the insulation was missing. It looked like it would be a lot of trouble to replace those old wires, because they seem to disappear into the wiring harness. They also go up inside a mounted metal tube that protects them.

Do you happen to know what those small black plastic... cylinders are, that are connected to those starter wires? They are in-line. It looks like they could be some kind of resistor. It would help if I could cut those things out and run fresh new wire.

Thanks to all for the replies!

 

[PhotonFanatic]

Well I checked the passenger side head ground as scrap-metal suggested, and it's broke off. So I've definitely got to replace that.

 

[75gmck25]

The wires with round barrel-shaped plastic around them are the fusible links. They are used on those wires instead of fuses. FYI - On my ‘75 they did not yet use the plastic barrel link - it’s just fusible link wire that burns up if the current is too high.

You can get replacement wire ends that have a ring terminal and a section of fusible link wire molded into them. The standard/ most common GM fusible link is 14 gauge, and it protects a 10 gauge wire. Most auto parts stores stock them. Newer trucks like yours may have the newer style fusible link that is marked in millimeters on the plastic barrel. https://www.amazon.com/dp/B000COD0TW/

On my ‘75 truck one of the small wires at the starter is the alternator charge wire and the other runs to the power junction next to the brake booster.

If you go to pick and pull you will find GMT 400 trucks (88 and newer) with a multiple terminal firewall junction that has several different sized wires with fusible links. Just remove the junction and take all the wires with it. I used one of these wires when I upgraded my alternator, since a 10 gauge charge wire seemed too small.

 

[Ricko1966]

Okay your battery grounds directly to the block. Starter and alternator are your biggest electrical produces/consumers and grounded by the block. Battery also grounds directly to core support, truck body from that point becomes a ground so you have a convient place to ground inside the cab,lights etc. The whole truck body is now a ground.You need a third ground,frame to battery,frame to truck block,or frame to core support/body. Those are the 3 primary grounds,check those first. The firewall ground to head is for ignition interference to radio at one time cars that were ordered with no radio didn't that ground. Headlights ground to core support. My money says the wires you repaired need repaired,your lights and radio were fine before you cut and spliced those.

 

[PhotonFanatic]

Okay your battery grounds directly to the block. Starter and alternator are your biggest electrical produces/consumers and grounded by the block. Battery also grounds directly to core support, truck body from that point becomes a ground so you have a convient place to ground inside the cab,lights etc. The whole truck body is now a ground.You need a third ground,frame to battery,frame to truck block,or frame to core support/body. Those are the 3 primary grounds,check those first. The firewall ground to head is for ignition interference to radio at one time cars that were ordered with no radio didn't that ground. Headlights ground to core support. My money says the wires you repaired need repaired,your lights and radio were fine before you cut and spliced those.

Yeah that's gonna be fun. Looks like it's time to drop the starter again! lol

Does anyone know what gauge the starter wires are? To me it looks like it might be 10 guage... maybe 14 gauge I'm not sure.

 

[Jgonick]

Looking at wiring schematics for 87/88 it appears to be 5 PPL (10 gauge)

Which is odd to me, because earlier than 87 the starter wire was 3 PPL (12 gauge)

You might want to get someone else to confirm.

Edited--- I forgot it went to R/V. I bet I was looking at 4th generation wiring. Sorry

 

[gmbellew]

the 1990 wiring diagrams for the R/V suburban show the purple starter wire is 3mm, or 12ga

 

[PhotonFanatic]

Anyone know why the starter wires are 12 gauge, but the fusible link wires are 14 gauge? I'm an electrical newb, but it seems like the fusible link would need also need to be 12 gauge. But all my searching reveals they're 14 gauge. And they just connect the smaller diameter fusible link to the larger 12 gauge wires.

2 NOS FUSIBLE LINKS! GM GMC TRUCK SILVERADO SIERRA C10 S10 JIMMY 1500 2500 3500 | eBay

These help stop electrical issues that can cause great harm to the wiring system if there is an electrical short. This Fusible Link Pigtail is exactly like having a fuse inside the wire! A real life saver if/when a problem occurs!

www.ebay.com

 

[Bloodhound1981]

Anyone know why the starter wires are 12 gauge, but the fusible link wires are 14 gauge? I'm an electrical newb, but it seems like the fusible link would need also need to be 12 gauge. But all my searching reveals they're 14 gauge. And they just connect the smaller diameter fusible link to the larger 12 gauge wires.

2 NOS FUSIBLE LINKS! GM GMC TRUCK SILVERADO SIERRA C10 S10 JIMMY 1500 2500 3500 | eBay

These help stop electrical issues that can cause great harm to the wiring system if there is an electrical short. This Fusible Link Pigtail is exactly like having a fuse inside the wire! A real life saver if/when a problem occurs!

www.ebay.com

The fusible link needs to be a smaller gauge than the wire it's protecting so that it fails first.

 

[Jgonick]

Fusible links are usually 4 gauge sizes smaller.

Example- Image 2. Red dot is wire - 5mm(10 awg) and blue dot is fusible link- 2mm(14 awg).

also I attached conversion table because a lot are metric sizes in diagrams

 

[PhotonFanatic]

Anyone know the reason why those starter solenoid wires (there's 2 iirc) can affect the headlights? The would seem to be unrelated.