Headlights and dash lights dimming

[Sp0okfish]

One night driving my 1986 m1008 i noticed that my headlights and dash lights will dim and go to back to normal. When they go dim and back to normal i can also hear what sounds to be a relay or solenoid pulling in or out. I can never duplicate it though. Its totally random some times it will do it really fast back and forth or several seconds between or I can drive several miles and it wont do it.

 

[cucvrus]

Sounds like the 30 amp fuse in the fuse box is cooking and welding itself fast. Check out the 30 amp fuse on the right side mid way up on your fuse box. Is it getting hot?

 

[Sp0okfish]

Will do that tomorrow. Also to add the Solenoid noise that i hear every time the lights dim sounds identical to when the glow pugs cycle on and off. I was wondering if somehow they were randomly cycling on and since they draw so much power if thats why my lights are dimming. But its hard to test it with a meter because it doesnt do it when idling only when moving.

 

[painter paul]

Does the glow plug light come on when the lights dim?

 

[Sp0okfish]

Does the glow plug light come on when the lights dim?

No it does not, but i thought that after your "WAIT" light went out and the truck is running the glow plugs come back on for a few seconds to help with warming up the engine and it does not make the light come on. I have also tried another glow plug control module that is in a friends truck that is good and still have the same problem.

 

[painter paul]

You could run test leads to the glow plug solenoid and Watch the meter while you drive.

 

[AECS]

Sounds like the glow plugs are going through the after glow process, perhaps a temp sensor or an intermittent short in the control wiring?

 

[Sp0okfish]

ok i checked the fuse the 30 amps fuse looks fine but mine is mid way up on the left not right. for hooking up a meter i could use alligator clips to see while driving which post would i stick the negative and positive to.

 

[Sp0okfish]

ok i checked the fuse the 30 amps fuse looks fine but mine is mid way up on the left not right. for hooking up a meter i could use alligator clips to see while driving which post would i stick the negative and positive to.

also to add that sometimes when the lights dim too the sound of the solenoid is very similar to like if you were to bounce a ping pong ball and then hold it close to the surface that you bounced it making a really fast noise.

 

[painter paul]

Put the red(hot) clip to the side of the solenoid that goes hot when you first turn the key on( the side that goes to the glow plug), then put the black ground clip to a good ground such as the base of the solenoid where it bolts to the truck. Sounds like your solenoid may be bouncing in and out and not staying locked it. Try the meter and let us know what you find,.

 

[tim292stro]

Sounds like a bad wire or ground issue with glow plug control...

You are correct, the "WAIT" light does not equal glow happening, just pre-start-glow. Depending on coolant temperature, they may be a minute or so of after-start-glow. If the glow controller is trying to glow afterwards and there is a broken/intermittent wire in the harness, it would cause the GP really under the hood to "bounce" (your ping-pong ball analogy is spot-on, in the electrical industries we call this contact bounce - basically the same principal as a mechanical buzzer).

Would be cool if you could take a video of this and post it via Youtube.

 

[Sp0okfish]

Sounds like a bad wire or ground issue with glow plug control...

You are correct, the "WAIT" light does not equal glow happening, just pre-start-glow. Depending on coolant temperature, they may be a minute or so of after-start-glow. If the glow controller is trying to glow afterwards and there is a broken/intermittent wire in the harness, it would cause the GP really under the hood to "bounce" (your ping-pong ball analogy is spot-on, in the electrical industries we call this contact bounce - basically the same principal as a mechanical buzzer).

Would be cool if you could take a video of this and post it via Youtube.

I have to go and pick up some alligator clip test leads this week to see if it is my glow plugs coming on and off. I will try and make a video with my gopro and hopefully yall can here the sound over the engine. Also how would I test the wires to see if they are broken isn't it called ohms. How many ohms should i read if wire is good or vise versa what will it read if they are broken.

 

[painter paul]

Make sure you get long enough leads to reach or just extend them with pieces of insulated wire