Can anybody help me figure out what this relay is for and what would cause the connecting pin to overheat and melt the connector? Fortunately I was working on something else and had the hood open, because when I turned the key to the "on" position, smoke started coming out of the relay. I'm just glad I didn't have a vehicle fire inside my barn...


50 amp automotive fuse



Was mounted on the driver's side inner fender

 

It is not a stock relay and the red wire to ground is not a stock color to use for that either.
It may have been for a snow plow or sander or extra lights.

 

Nothing on the truck is stock.....I think it may be partly tied to the ICM, but I need to unbundle some wires to be sure. I'll have to do some investigating myself to figure out what the relay powers, but one thing I can't answer is what caused it to melt? Would a faulty relay typically melt or is the problem somewhere in the wiring itself? Bad ground?

 

A bad ground would not cause a relay to melt.
Maybe too high a voltage on the relay coil would (Putting 12 volts to a 6 volt relay).
It would be a short to ground or a high load on the wire that is leaving pin #87.
Trace where the wire on pin 87 goes too.

 

Thanks, I'll take a look. What's strange is that the relay has been there as long as I've owned the truck. I have not made any modifications to the wiring.....just seemed to happen out of nowhere.

 

The contacts shorted due to high current draw. You say it has a 50 amp fuse to it? Those little relays aren't typically good for more then 20-30 amp. Whatever it is powering is bad/shorted.

 

I said I hadn't changed anything in the wiring, but I DID replace the starter the night before. I guess that is technically part of the wiring since it's an electrical component. I had just finished cranking the engine when I noticed the smoke. Turning the key to off made it stop smoking. Turning the key to on without cranking made it smoke again. I was not ballsy enough to try for a third time.


I am mentally challenged when it comes to wiring. How can I trace the short? I have a multimeter - could I check each of the 5 contacts in the wiring harness that the relay plugs into and learn anything useful?

 

Remove the relay from the plug and turn the key on. It should not smoke and you should be able to see what doesn't work now. Fuel pump? Or some other item that the previous owner added. You may just have to cut all the tape and trace down where the leads go.

The relay has a diagram showing what pins do what. Like subford mentioned, #87 is the item getting power. So pull the plug and look at the bottom of the relay(where the pins are-they are marked) and see what wire goes to #87. Trace that wire and see if it has a bare spot or find the item it powers and see if that item is damaged.

The starter solenoid is on the passenger fender next to the battery so replacing the starter should not have cause any problem. I say "should not have" unless the previous owner did something???

 

Pin 87 is SUPPOSED to be the load side of the relay, yes. But remember that a lot of people who do this stuff don't to it right, so you have an equally good chance a finding the power source connected on pin 87 and the load (item being powered) on pin 30.

 

The previous owner did a lot of ???? things. I'll keep digging.

 

What year and engine of truck? I see a Dura Spark 2 ignition box under your hand in the 2nd photo. Was the engine EFI and converted to carb/DS2?

 

I am guessing he is working on his 1987 F250, 460, ZF 5 Speed, 4x4, 33"BFG, RCLB.
The Dura Spark 2 ignition box is stock for that truck along with the carb.

 

My truck has a long and questionable history. It was originally an EFI 351W. Previous owner pulled the engine/AT/EFI systems/etc and slapped in a 460 with a ZF-5. Most of the wires under the hood are a compilation of 5 or more short sections of wire all spliced together to make one long, janky wire.

 

Final update: The short happened after leaving my truck in the rain overnight (usually it stays indoors). I removed the plastic conduit/tape holding the bundle of wires together that the relay feeds into and noticed that the bundle had gotten wet inside. There was a bad splice with bare wire showing that had gotten wet. I let everything dry out, replaced the relay, and fixed the splice. The truck is (FINALLY!!) up and running with no apparent issues.

 

Oh yeah, forgot to mention, it was an ignition relay.