Any Known Problems With '72 MC7 Turn Signals/Emergency Flashers?

oldmansax · June 12, 2011, 01:43:41 PM

When I first bought my MCI, I had trouble with the emergency flashers. After about 3 minutes, they would burn up the flasher. This problem has gotten worse over the years until now, as soon as I turn on the flashers, they burn up the flasher. The signal lights always worked fine until the last trip. I turned on the left turn signal & it would not flash. Tried the right & it would not flash either. When I turned on the left one again, it burned up the flasher.

I have already replaced the flasher with a heavy duty mechanical one. Since the turn signals and the emergency flashers used the same flasher, I assumed for a while the emergency flasher switch was failing & I could replace that & fix the problem.

I already know how to systematically trace down the problem, whatever it is.

What I need to know is, has anyone else had this symptom and if so, what turned out to be the problem, and/or, is there anything in the system that has been shown to be weak & I should look at it first?

Just trying to save myself some time here, I have a potential buyer coming to look at it this week & want it to be ready.

Thanks!

TOM

gumpy · June 12, 2011, 06:47:51 PM

Well, I don't know much about the MC7 electrical system, but it's not much different from the MC9. I'm not aware of any common problems that would cause
this. I think you should be looking for a shorted wire in the system someplace. It sounds suspiciously like you have a hot wire that is shorting to ground and for
whatever reason, your circuit breaker is not tripping before the flasher fries.

Just my two cents... and worth every penny of it...

fe2_o3 · June 12, 2011, 10:06:59 PM

My first thought is some one put a 12 volt flasher in a 24 volt system. Are you using the part # from the book or just replacing with what was in there?...Cable

gumpy · June 13, 2011, 04:37:03 AM

Quote from: fe2_o3 on June 12, 2011, 10:06:59 PM
My first thought is some one put a 12 volt flasher in a 24 volt system. Are you using the part # from the book or just replacing with what was in there?...Cable

Good point. That could certainly be possible.

However, I believe original wiring used the oblong flasher units that MCI uses in the bank of flashers within the front J-box.

Is the flasher that's burning out the OEM unit?

oldmansax · June 13, 2011, 04:02:30 PM

I started trouble shooting today.

First, the flashers are all 24 volt Signal Stat electromechanical units. I have used about 8 or 10 of them since I had the bus. The original flasher was replaced by somebody a long time ago. When that was done, the indicator light was rewired to the new flasher; however, when I removed the panels by the drivers seat to check things out, it appears the original oblong relay is still connected. It is labeled "turn signal relay" in the schematics & has 3 terminals and what looks like a resister & maybe a diode across 2 of the terminals. I briefly checked each light circuit (terminals 6,7,8,9) by themselves & all the lights light with no apparent shorts or over amperage. I had to pull off checking the lights & go to another job but I am going back tomorrow ( I hope). I am not real sure what the relay was suppose to do it the original circuit & I didn't have time to look at the diagrams very closely. I remember the diagrams said "flasher" by the relay. Craig, is that the original flasher? I guess made into one by the use to the resistors & whatnot? If so, I would think it would have been abandoned when the Signal Stat was added.

Just guessing here...

All of the wiring is original except the new flasher & looks to be in very good sh shape, no hard insulation or chafed places.

Still looking.....

TOM

harpold700 3 · June 14, 2011, 09:06:56 AM

My 4 ways will cut out when used for any length of time. They always come back on line, must be circuit breaker in line. Stopped using them continuosly, work fine on light (no pun) duty. Have to get into it later??? Gord

oldmansax · June 14, 2011, 02:15:15 PM

Found my problem. The "Turn Lt Relay", which is the oblong Delco Remy relay in the circuit, had come apart on the inside & was shorting out. That caused the flasher to fail. I removed the relay from the circuit since all it did was light the indicator light. That function is now performed by the 3 prong flasher.

TOM

Slow Rider · June 17, 2011, 11:37:03 AM

Glad to hear it was an easy fix and thanks for sharing the results Tom. I am still waiting for you to drop by for coffee

Frank

oldmansax · June 17, 2011, 03:32:50 PM

Quote from: Slow Rider on June 17, 2011, 11:37:03 AM
I am still waiting for you to drop by for coffee

Frank

I know!! I'm pretty trifling aren't I? At the rate I'm going, I will have sold the MCI before I ever get over there. I actually have someone who is coming to look at it next week.

I guess I will have to drive over in the car.....

TOM