Electrical malfunction/MC-9

[robert.loya@att.com]

My MC-9 ('83) instrument panel guages & high idle do not function,,,I'm thinking it could be a defective circuit breaker,,,The numbered terminal board (front junction box) also seems to be dead (no current),,,,I tested a few terminals with a fuse/light tester and it didn't show current(dead)...I also temporarily connected a by-pass wire(hot) to the high idle switch & was able to get the engine to high idle mode....Has anybody ever experienced this problem??,,I would appreciate some assistance on this matter from anyone,,,Thanx,,,B

[Dreamscape]

Welcome!

Do you have an electrical schematic? Trace it from there. I know gremlins can be a bugger, but it helps to have some documentation.

I"m sure the MC electrical folk sill be along shortly to help you out.

Paul

[buswarrior]

I don't know...how about the big cable succumbing to corrosion that feeds the bar?

Get your schematic and work forward/backward to/from the batteries, you'll find where the power stops and dig in deeper there.

happy coaching!
buswarrior

[robertglines1]

ck ignition switch make sure power in and out to terminals that need to be hot also ck power in and out to solenoids in front box:when powered up the solenoid should push current Thur to other side,just guesses a place to start....when you jumped the high idle did everything else work;if so is same circuit...

[gumpy]

Well, you're going to have to get more specific here.

How did you start the bus if the front busbar is dead? Where did you jump the high idle from?

There is a 105a circuit breaker in the A/C junction box that feeds the front 24v busbar.  Then there's a 30a circuit breaker on the front busbar that feeds the master switch.
Do you have power on the front busbar?

[bevans6]

My MCI is probably similar enough to yours that this may help.  If not, I tried!

The fast idle and many of the dash functions are powered through stud 26 (and 19) on the front panel.  It is powered from the front main buss through a 30 amp breaker that feeds the master switch, from there through a 6 amp breaker that feeds a secondary buss bar.  Stud 26 is connected directly to stud 19.  You should have power on the main buss whenever the battery disconnect is on, and you should have power on the secondary buss and stud 26 whenever the master switch on the dash is on.  

The 30 amp breaker is number 4 of the main buss, which is the lower bank, left most position.  The 6 amp breaker is on the secondary buss that is located directly to the left of the main stud panel, and is number 3, which is the right most of breakers on that buss.  The breaker numbers don't relate to position, just to reference numbers on the schematic, as far as  I can tell.

Stud 26 feeds all the buzzers, the hot engine and low oil pressure sensors, the parking brake and stop lamp switches and fast idle, the stop lamps, and at least some of the gauges.  I bet the 6 amp breaker is bad (it's an autoreset), or the main switch is bad and isn't feeding it, or there is something bad downstream of stud 26/19 shorting the whole mess out and causing the breaker to correctly disconnect the lot.

Brian