QuestionCan you please help? My #8 fuse blows, then i would replace it and it would be fine for a week or so. It now blows almost every start. I have replaced the ignition switch and am not sure if it is the starter.
AnswerHi Larry,
I assume this a convertible, rather than a sedan. Please let let me know if otherwise.
I think the first thing to do is see if turning the ignition switch to run causes the fuse to blow, and if not verify that it blows when then try the start position. If it blows in run, then the starter motor circuit is off the table as a possible cause of the problem.
There are several separate circuits drawing on that fuse, so you will need to check the resistance from the side of the fuse socket labelled #54 to ground (- post of the battery) while the fuse is removed (so there is no voltage on the #54 side), and the ignition switch in run or start which ever of those positions causes the fuse to blow, while you then begin to detach the components of those circuits until you find one that allow the resistance to ground do rise above 2 ohms which would be high enough to keep the current low enough so the fuse wouldn't blow. You should find the resistance when you begin to be below 1 ohm which is why the fuse is blowing. That component which is faulty, when removed, will produce a jump in the resistance measurement.
The wire attached to #54 is red and it goes to:
1.the fuel pump relay and then when the relay is activated, in both the run and the start positions of the switch, the current goes to the fuel pump motor on a dark green/white wire. So it is possible that the fuel pump is shorted to ground or the wire on the way to that pump is shorted to ground.
2. the ignition switch where in the start position it sends current on a dark blue wire to 10 amp fuse #10 (which should protect it from being blown by blowing first) and from there to the activation coil of the fuel pump relay. I think this circuit is not the one that is shorting your fuse. The same dark blue wire provides power to the body control module, but that also is not likely to draw 2o amp.
It also provides current to fuse 17 (10 amp which protects it) that goes to the airbag control module, but that fuse and module probably aren't the problem. It also sends current thru fuse 10 to the powertrain control module and the ABS control module, but as with the activation coil of the fuel pump relay, the #10 fuse would protect fuse 8 from blowing.
3. the starter motor relay and when that is activated by the ignition switch the current goes to the starter solenoid on a brown wire. That solenoid could be bad or the brown wire could be shorted to ground if the fuse only blows when you try the starter position, and it doesn't blow in the run position of the ignition switch. So it is relevant to see when the #8 fuse blows.
4. it also sends current thru fuses 14 and 15 (10amp) but those should protect it. Those power a number of low current devices that should cause either 14 or 15 to blow first before #8 would blow.
5. it provides current to the actuation coil of the starter motor relay in the start position of the ignition switch which is involved in the starter safety interlock circuit that keeps the engine from being started except in park or neutral, including the transmission control module which shouldn't drain it enough to blow the fuse. So those are probably not involed either.
6. it provides current to a number of other actuation coils of relays and solenoids thru fuse 9 and 10 which should protect it.
So looking over that list I suspect that either the fuel pump is over-drawing the current supply or the starter motor solenoid is over-drawing the current supply and blowing the #8 fuse.
So I would begin by pulling the fuel pump relay and see how the resistance rises, and then the starter relay and see how the resistance rises when you try the ignition switch. Pulling one or the other of those relays will give you the answer, I suspect. If you don't have an ohmmeter you can just buy a box of 20 amp fuses, and try by an "acid test", seeing if the fuse blows first in the run position (which would implicate the fuel pump as the culprit, or in the start position which would implicate the starter solenoid as the culprit). But keep in mind that it could be the wires to those two devices that are shorted to ground rather than the devices themselves though chances are the device is bad, not its wire.
Let me know what happens...
Roland
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