Rev counter issues.

Marcos Graveyard · Post by **Marcos Graveyard** » Mon Aug 29, 2016 8:36 pm

Hi,
After buying a Megajolt 6 years ago I finally got around to fitting it to my Mini Marcos.

I am however having some teething problems.

I have the hard rev limiter fitted as well as a tacho driver from Trigger-Wheels and a shift light.

My issue is that my rev counter will now not rev past 2000rpm, when it reaches 2000 the needle drops down to 0 until the revs drop below 2000 again whereupon it will register the correct revs. The rev counter on the connected lap top is unaffected and measures the revs throughout the rev range.

I also cannot get the shift light to work fully, it's a 2 colour light but only 1 colour will illuminate. I wonder however if I have made a mistake in my connections.

Here is my wiring diagram, could some one confirm that all is as it should be.

A few pics of my instillation

Thanks in advance.

Marcos Graveyard · Post by **Marcos Graveyard** » Sat Sep 03, 2016 5:45 pm

I've sorted my Shift Light problem, I had the light wired incorrectly, the first stage light needs to be connected to a user output with a specific designed rev limit at which to operate. I chose U/O2 as it was the nearest pin to where the green wire from the shift light was. Getting those pins out of the plastic block is a right pain. Pin switched over and all was good.

Here is the new diagram.

The problem with the rev counter still persists, I have uploaded a video to YouTube to sho exactly what's happening.

https://www.youtube.com/channel/UCFlAbS ... u3qnxR5ywA

toenee · Post by **toenee** » Wed Oct 05, 2016 9:27 pm

I have exactly the same problem, mini with a MGB rev counter.
Some where on the forum theres a suggestion to remove one of the resistors on the tacho conditioning board. Just not got around to trying it yet.

Marcos Graveyard · Post by **Marcos Graveyard** » Mon May 08, 2017 7:53 pm

I have eventually rectified the problem. I searched through many posts on this forum and quite a few other sites too, there were many suggestions and opinions on how the problem could be fixed. Searching for my particular rev counter revealed that fixes that worked for one person, didn't work for another. So all I could do was work my way through each option.

Firstly I removed the rev counter from the dash, a job that woyld be much simpler if my arm had about two more elbows. The first option I tried was the Clean Tach Out pin (pin 11) on the EDIS unit, I drilled out the blanking plate and removed the plastic plug. I removed the connector and soldered a new wire to it and reassembled the whole thing. I connected up the rev counter and started the engine. Nothing, not a flicker. It did however work perfectly with a small 52mm no-name rev counter, but that wasn't going to look right in a 45 year old car.

Next I did a bit of research on fitting a pull up resistor to the rev counter but nowhere could I find a definitive value for such a resistor nor was there any good information on where exactly you would fit the resistor. So I looked at the next option.

The tach out pin on the Megajolt itself. Again I wired up a new lead to the plug and connected up the rev counter. Success !!!!!

Rev counter worked flawlessly. Then followed three hours of unraveling wiring loom and running the new cable behind the dash to the clocks. Again contorting myself trying to refit the rev counter and getting the mounting nuts back in place but at least now I have a working rev counter fitted to my Marcos.

Happy days.

toenee · Post by **toenee** » Mon May 08, 2017 9:59 pm

Nice one, very nice Marcos as well, was at the Mk1 conversions track day the other week. Not seen so many marcos's gtm's etc. Usually quite a strong irish contingent as well.
Should really get around to sorting mine, funnily enough I never got anything out of the megajolt tacho output. Obviously need to look at this again.