Pulsing lights

Thunderbirb

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I am wondering if your glow plugs are cycling when the lights are pulsing...
One of the mods that the previous owner did to this truck was add a toggle switch for the glow plugs so In the morning when I try to start it I have to flip the switch for a few seconds to let the glow plugs heat up and then the truck will start. I don’t think it would be the glow plugs cycling just for the reason. Like I said before the previous owner did a lot of weird wire cutting and splicing that I have to fix.
 

Selahdoor

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One of the mods that the previous owner did to this truck was add a toggle switch for the glow plugs so In the morning when I try to start it I have to flip the switch for a few seconds to let the glow plugs heat up and then the truck will start. I don’t think it would be the glow plugs cycling just for the reason. Like I said before the previous owner did a lot of weird wire cutting and splicing that I have to fix.
Yet you trust that he did the wiring correct for the glow plugs? :D
 

Thunderbirb

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I think it's still a grounding issue. The cluster is not grounded properly, that is the reason you think it's getting hotter when it's really not. The cluster needs to be grounded, the cab needs to be grounded and the front sheetmetal needs to be grounded. The factory had a ground strap from the rear of the engine to the firewall. There is another grounding point for most of the truck behind the radio up high on the inside of the firewall. I would just run a short ground from the radiator support to the negative cable for the frontend.

I was working on a very rusty truck, and I ended up having to ground the alternator with a extra wire. It should be grounded through the brackets, but they were so rusty and they were all frozen.
I do want to go through the dash and fix the wiring problem because the previous owner cut a lot of wires and did some weird splicing. Wish I could find a truck that I can steal the wiring harness from to fix everything but it’s hard to find any junk trucks here around the same year I need. I’ll try going through the dash and seeing if I can find any issues. I’ve been wanting to open up behind the cluster anyway so I’ll give it a shot will some new grounds!
 

Thunderbirb

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This is how my wiring is and it’s such a rats nest of problems. I did find a couple grounds that weren’t connected behind the radio!

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chillman88

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I suspected a bad ground so I ran a test today to check if that could be the issue. I connected the jumper cables up , one clamp to the body of the truck and the other end directly to the negative on the primary battery but even doing that I still saw the lights do the same thing. The lights did brighten up when I connected it that way so I’m sure I can improve the grounding. I’ve even tried mismatching where I connected the engine directly to the negative terminal but didn’t see any change. So I’m pretty positive that’s it’s not a ground issue. I’m going to try to use the regulator behind the dash and see if that works

If the lights got brighter then they definitely have a ground issue. I'm not saying that's your problem, but sometimes these things compound themselves. There should be a couple grounds right near the headlights, I'd clean those up and possibly ad another ground strap from them to the battery.

I've heard of some weird things happening when grounds are insufficient and it tries to ground out through other things it's not supposed to.....

I don't have a voltage regulator anymore, upgraded to a newer alt with it internal. How does the voltage regulator ground? I know you replaced it, but if it's not getting good connection that could be part of it too. Were the plugs on the harness corroded at all when you changed it?
 

Thunderbirb

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If the lights got brighter then they definitely have a ground issue. I'm not saying that's your problem, but sometimes these things compound themselves. There should be a couple grounds right near the headlights, I'd clean those up and possibly ad another ground strap from them to the battery.

I've heard of some weird things happening when grounds are insufficient and it tries to ground out through other things it's not supposed to.....

I don't have a voltage regulator anymore, upgraded to a newer alt with it internal. How does the voltage regulator ground? I know you replaced it, but if it's not getting good connection that could be part of it too. Were the plugs on the harness corroded at all when you changed it?
I will be fixing the grounds a little better now and going through all the wiring of the dash to fix the issues that I have. I have a lot of wires though that I can’t find any diagrams for. I’m planning on fixing the grounds especially since I found some ground wires behind the dash that weren’t connected!
 

Thunderbirb

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If anyone has any diagrams for wiring going from engine bay through the firewall to inside the cab. I have some wires that I’m trying to find matching ones too but it’s starting to get difficult and some that look the same are different gauges so it’s confusing me a bit. The lights that turn on usually to cycle the glow plugs have never worked for me since the previous owner bypassed it and connected a wire directly to the relay to turn it on and off with a toggle switch. So far I haven’t tested. I just want the wiring to be in a better state when I do try to start it up.
 
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IDIBRONCO

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I am wondering if your glow plugs are cycling when the lights are pulsing...

Yet you trust that he did the wiring correct for the glow plugs? :D

Well you are right about that. I really don’t trust it that much so i should really suspect it too I just don’t know where to start in fixing this wiring.
Due to the simple fact that the truck still starts, the glow plugs aren't cycling and the toggle switch is probably wired up right (maybe not safely though). If the glow plugs were constantly cycling while the engine was running, they would quickly burn out. They also wouldn't cycle faster as the RPMs rise. They would still cycle at the same frequency.
 

Thunderbirb

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Due to the simple fact that the truck still starts, the glow plugs aren't cycling and the toggle switch is probably wired up right (maybe not safely though). If the glow plugs were constantly cycling while the engine was running, they would quickly burn out. They also wouldn't cycle faster as the RPMs rise. They would still cycle at the same frequency.
I do think it is a few bad grounds since I found a couple that were not bolted down behind the dash. I’m working on fixing a lot of the cut wiring to make it stock again. The glow plug toggle switch was wired up very unsafe where one wire was connected to a random fuse and he added an extra wire that went through the firewall to connect to the glow plug relay to make it work. I just took it out yesterday and wiring is almost fixed. I can put the dash back together and test it out!
 

Thunderbirb

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Update on the lights. After some wiring I have managed to get the the lights to stop pulsing. I do believe it was a bad ground behind the dash but I do think I still wired some things incorrectly. The tachometer hasn’t worked since I had the truck and I tried to wire it up following the diagrams but couldn’t get it to work still. And now I find that my engine temp warning light is on Even when it’s a cold start. And I have a concern now that my glow plugs are not turning on because it thinks the engine is hot. There is still a lot of wiring to go. I think I’m going to look into getting a parts truck and stealing all the wiring from it to replace mine.
 

IDIBRONCO

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And I have a concern now that my glow plugs are not turning on because it thinks the engine is hot.
Nope. They will still work. The controller gets it's temperature directly from the coolant and has nothing at all to do with the engine temp light.
 

tonyj54

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Thanks for this post. I have an '86 F-250 Supercab, 6.9, with some similar issues. Haven't ever noticed pulsing lights, but, then, I seldom, if ever, drive in the dark, either. Don't want to hijack the thread, so Mods feel free to kick this or open new thread.

I just replaced glow plugs, adding pushbutton for pre-heating. He still hates first-start, though. Once I've gotten him running first-time of the day, no problem. But, apparently, he's not a morning person. Lol. I'm not sure coffee into the intake will help, but not opposed to trying, I suppose.

My other issue is the one that drives me a little nuts. He has an after-market cluster installed just below the dash with charging, oil pressure, and temp gauges. Once started, charging gauge needle pegs to left side of the gauge, and only reads correctly after I turn on headlights. I suspect a ground problem, also, but it appears that my wiring behind the dash may have been done by the same guy as OP. In other words, it's a rat's nest. I've had the truck going on six years, and drive it with no electrical problems, other than the aforementioned gauge anamoly.

I'm admittedly not a gearhead, should have spent more time under the hood with my Dad, but any help Will be greatly appreciated.

Thanks. Be well.
 
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