87 f250 fuse 15 blows when starting the truck
- Thread starter John_piv
- Start date
hacked89
Full Access Member
does it still pop now with the cluster unplugged? If yes, I would start tracing that red and yellow wire. Goes quite a few places. Instant fuse pop is a short to ground like Nero said. Start tracing the red yellow from the warning buzzer, the low vacuum switch and the water sensor. Make sure you lift and look at all sides of the wire as you move along. You can also try unhooking these components one by one as an easy test for internal short.
hacked89
Full Access Member
I’ll tackle any short to ground with a car headlight, wiring diagrams and multi-meter. And you can too. If your feeling like you want to take it a step further than just tracing wires, connect one end of a car headlight bulb to 12v at your battery and the other end into the 12v wire that you believe is short to ground. If it is indeed short to ground than the headlight will be on. Then you start unplugging components and tracing until the headlight goes out. That’s when you know you found it.
Yep, still blows with the cluster unplugged. It does something weird that I've never seen before. If you have no fuse in there, the glow plug controller doesn't work. If you put a blown fuse in there the glow plug controller will work. I'm guessing my problem is on the red and yellow wire, cluster side because everything on the other side of the engine seems to be working.
Y'ALL I FINALLY GOT IT!!! I went through the wiring diagrams and pulled everything it connected to one piece at a time. Ended up being the low vacuum sensor in the engine bay. Disconnected that, put a new fuse in, and fired the truck up. All my gauges work fine. Is it even worth replacing that part? I've had my vacuum pump go out once and there was no warning light. I may not mess with it anyway now that I finally got it back together!
Thanks for the guidance y'all!
Thanks for the guidance y'all!
hacked89
Full Access Member
Glad to hear it was one of the three we talked about. It’s there for safety because your brakes run off vacuum booster unless you have hydroboost.
I personally do not think the warning is needed. By the time it comes on it's too late for the brakes anyway. I have a theme going with my truck; If it breaks and it turns out I don't need it, I don't replace it. Then it can never break again. So I have lost;
The glowplug automatic control. Went to manual control.
The cold start/advance system
The fuel heater in the top of the fuel filter
The mechanical fuel pump (went bad, replaced it with electric)
The rear abs junk.
The front side fuel tank and fuel switching valve.
The rear self-adjusters on the brakes
Oh, and of course the low vacuum warning system.
My truck gets more and more reliable.
The glowplug automatic control. Went to manual control.
The cold start/advance system
The fuel heater in the top of the fuel filter
The mechanical fuel pump (went bad, replaced it with electric)
The rear abs junk.
The front side fuel tank and fuel switching valve.
The rear self-adjusters on the brakes
Oh, and of course the low vacuum warning system.
My truck gets more and more reliable.
Noiseydiesel
Full Access Member
Smoking the fat brown wires originally, did you melt the connector and cause other issues inside the plug? One fix is to remove the fat brown wires from that plug and join them separately outside the plug.
I suspect the start (crank) circuit is back feeding the run circuit.
Fusible links are easy enough to check. Pull on them. if they stretch out, they are internally melted.
"#18 fuse runs gauges and everything else. . ."
You might be chasing the wrong side.
Investigate the crank side.
That wire goes where, through what, near what?
The GP relay gets 12V constant through a pair of fusible links, no? Those two wires go through that fat connector and may have melted/joined other wires together also, no?
I suspect the start (crank) circuit is back feeding the run circuit.
Fusible links are easy enough to check. Pull on them. if they stretch out, they are internally melted.
"#18 fuse runs gauges and everything else. . ."
You might be chasing the wrong side.
Investigate the crank side.
That wire goes where, through what, near what?
The GP relay gets 12V constant through a pair of fusible links, no? Those two wires go through that fat connector and may have melted/joined other wires together also, no?
No. The glowplug controller "brain" is fed by the red/lightgreen ignition wire that also feeds the injection pump solenoid, the fuel heater, etc. The fat wires only feed the glowplugs themselves.
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Old Goat
Full Access Member
Once you remove all the krap, your mileage picks up from dragging around all that weight......
I removed the Vacuum thing that is suppose to turn the low Vac light, which didn`t work.
Applying the Brakes and almost going through a Stop sign is a better indicator....
I don`t have a tachometer, so in that space I drilled a 2 1/16" hole and installed a Stewart Warner vacuum Gauge.
Went Manual GP` and works every time.
Also give you more control for an after Glow if needed when super cold.
Goat
I think at this point, most of those vacuum sensors don't work anymore. We were wotking on my Son's 90 4x4 IDI. The lift pump had a pinhole in it, spraying fuel everywhere. To replace the lift pump, we pulled the vacuum pump for room. To test it out before we buttoned everything up, we fired up the truck. The vacuum pump and bracket was lying on the air cleaner lid (yes the air cleaner was still where it belonged) and no red BRAKE! light on, and I can 100% verify the pump was not working.......
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