Blowing Engine Control Fuse 30A, Im bad at electrical.

I have gotten a pretty good start at tackling the problem thanks to this site and others, but I am getting tired of blowing fuses so any extra help would be great!


1992 Comanche 5 speed 200k mi
Just purchased it drove it 2 hours home, cel came on. it was 33 (no ac), and 53 (ecu).

Changed the starter bcus it was bad, worked great.

Fumbled with the ignition cylinder thinking it was broken, long story short there is a lever you push to lock the cylinder.
I connected a non oe wire thinking it should probably be connected.

Now it turns, but wont start and blowing 30A Engine Control Fuse.

My dad put a 60A in and it didnt blow, but didnt start. I know that was a bad idea.

I disconnected fuel pump relay, no start no blown fuse.
Disconnect fuel pump, blown fuse.

Disconnect the oe wire that was previously disconnected and it starts. But I hear a knock, and it shuts off. Fuse is good turn it on again, decide to try and drive it, close the hood and it shuts off. Try turning it on later and no start, blown fuse.



Visual inspection of 02 checks out
I know that my fuel gauge always shows just about empty. Disconnecting the fuel pump gives me way past empty fuel, my understanding is a short in the wiring. The Fuel pump gave me 66 ohms. Relavant?

Im starting to suspect I damaged some wiring in the ignition, but dont really know how to start.


PS no horn, or high beams, relay for horn works, I did hear the horns go off really quickly while installing the steering wheel but as a rule it doesnt work.




THANK YOU THANK YOU THANK YOU:yelclap:

Check the battery cables. I Had a lose cable going to the engine bay fuse box that blew the big fuse for the alternator.

Not sure about the rest of the laundry list issues. Some could be normal wear and tear, like the horns rusted out and blown high beems. Or you got bad electrical problems.

You might have broken the highbeem switch or loosened the plug working on the ignition
Check where the fuse box is under the dash does it look like it has been soaked with a leak from the clutch master cylinder.


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find the ballast resistor, bypass it.
if it's cracked it may very well be shorted.

check the cps/o2 wires running down the firewall. If they've come loose they will melt on the exhaust and short.
02 sensor will definitely pop that fuse.

ignition switch is a definite possibility, but they generally don't pop fuses, usually stuff in the interior stops working first. like the HVAC fan.

Thanks for the replies gents, I really could use any advice, im a terrible electrician. The reason for the laundry list is that I like to be detailed, I dont know if anything is related. At this point I just want the bad boy running, screw gas, screw high beams lol.

Battery Cables: Appear to be okay
High Beam switch: I know that there was a little bracket I forgot to replace, I think it was for the highs, but I didnt want to go back.
Fuse box Inside: looks dry, clean

Ballast resistor: never heard of it, I will look into it. Bypass? Does that mean I disconnect it from harness and add a jumper?
CPS: Appears okay, ohms check out, and wiring looks good
O2: looks good, when I get more fuses I will disconnect it and see if it still blows.
Fan: the fan inside works, but Im not a/c equipped.

Thanks again

ballast resistor drops the voltage going to the fuel pump for noise reasons.
to bypass it you just connect the two wires that go to it together.

on a renix jeep it's bolted to the fender on the drivers side behind the headlamp.
I'm not sure where chrysler put it.
IIRC it was used until 93-94.

91-92 The ballast is on the drivers side fender wall near the washer reservoir.
It's the only piece of ceramics there.

You can test it by bridging the wires by placing fuse there instead. It's a cheap part to replace right although some leave it bypassed.


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Just a quick update, I have a bunch of fuses for testing. But I decided to test other fuses first.

20A IOD fuse is blown, not sure if its going to blow consistently but yea.

Also wanted make sure to point this out, I did get a code 53 Internal PCM Failure, from what I read that means change it. Is that right?

Ouch. Code 53. Yeah I'd hunt for a new used one. I think it's 92-91 only for that year.
What I don't know is if you can put a automatic ecu in a manual. I though maybe you could.
Best way is to pull the ecu and match the numbers off it.


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Okay so I have a good update:

Truck runs, went on some light trails. threw some heavy stuff in the back, running like a champ.

I have the same ecu. Nothing really changed. My brother in law mentioned that it might have been blowing because it was a safety feature, once I had the battery disconnected for a bit, memory erased and its good.

I have no clue, but my truck runs great, might the PCM really be bad?

A fuse is a safety feature. It is there to protect the wiring/vehicle from burning up if there is a short.

Blowing a 30A fuse takes a major fault. For it to blow you have to be drawing 360 watts. That is more than enough to burn up just about any wiring in an XJ. Did you ever pull out the 60a fuse and replace it with the 30a?

If not, do that pronto. It sounds like you have/had a serious short somewhere. If the ECU was pulling that much power, you would have been smelling the magic smoke.

It seems strange that you were also blowing a 20a fuse. What does IOD stand for? I don't have a manual handy.

Thank you old man . I appreciate the concern. I am currently using the original 30A fuse and having no issues. I did get a cel but it disappeared before i could check it.

IOD fuse is Ignition off draw, reason my stereo has no memory . I do know that this truck has a major short, a buddy of mine warned me about it, and said trace that short before ever putting a fuse in it. I will try and find it in due time, unless someone points me in the right direction off the bat.

My hope is that I can get around in it with minimal problems, I love my comanche so much more than the xj so far.

what you need to do is get the list of things that the IOD powers.

on a 97 it's an odd list of things you wouldn't suspect, like o2 heater power.

then start looking at the wiring for those devices.
my bet is you will find a damaged harness that randomly shorts on the body.

be glad it's not the renix, or you'd be dealing with fusible links.