Fuse 18 Blowing - Short -

Igofaster13

Member
Mar 9, 2006
168
3
19
San Diego
Fuse 18 is blowing right when the key is turned to run position, checked the ignition switch (replaced a few years ago) looks fine & not falling apart. Checked most grounds/connections but everything is looking good. Kills alt/rpm/oil gauges. Use to happen every month or so but after new heads/3g alt/new ground to battery its usually blows right away. Any ideas/good schematics?
 
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Have you disconnected everything you can on the circuit and then reconnected them one at a time (with the key on) till the fuse blows?

Ok, just disconnected parts one at a time blowing fuses. Started at the cluster, removing one clip at a time. Then to the chime for the seat belt. Then to the engine I disconnected the main salt & pepper connectors... still blows. Only way is to disconnect ignition switch. Only thing I see is the connector for the ignition switch is a little melted from when it fell apart ages ago (going to replace). Any more thoughts?
 
There's a lot on fuse 18 (that link was not meant to list it all - an EVTM page is needed for that, and I don't know of one online).

If not disconnecting everything, I would really look at the wiring under the column and the engine bay sensors (the low oil level and coolant sensors are on that circuit and exposed, for example).

You might wanna rig up some jumper wires and a circuit breaker - it saves the expense of fuses while doing diagnostics. Note that any short is capable of starting a fire so use caution and proper safety.


Anyhoo, maybe someone can put up an EVTM page for ya. I'll send you a PM about something too.
 
89 Mustang wiring diagrams zip package– the 88 Mustang should be the same except for the computer & MAF wiring. None of that runs off fuse 18, so you should be OK. Catch me before Wednesday because after that I won't have access to the diagram set for some time.

PM me your email address and I will send you a complete Ford Factory 89 Mustang electrical diagram set. The zip file is 2.5 MB and is too big to fit through Stangnet's email gateway.


They are in a zip file format to reduce the size of the package. You’ll need WinZip or other Windows archive tool to extract them from the zip file. See www.majorgeeks.com - Download Freeware and Shareware Computer Utilities for a free download.

You will need the Adobe Acrobat viewer which is also a free download – www.adobe.com/products/acrobat/readstep2.html - Adobe Reader download - All versions
 
Thanks for all the help! Found the short. It was a short to ground in the harness driver side near the coil, in the bundle of wires right there. Cleaned it all up and insulated everything with tape/wrap. Used a continuity test via #18 fuse circuit short side to ground, while jiggling wires around till I found the intermittent short.