Autosport Labs

Hello All,
I'm having a problem with the option switch circuit, the one that switches between two maps.I have tested from the molex plug through the switch, and with the switch closed I have continuity all the way. However if I test for voltage across the switch when it is open I have 0 volts. How many volts should be across the switch? This problem seems to be intermittent as I have had this circuit work earlier and once saw the display flickering from one map to the other at idle. Any ideas would be welcome.
Thanks,

Paul, are you running a V3 or V4 controller?

Brent,
Mine is v4.
Thanks

Let us double-check a few things- I'll get back shortly.

Hi Paul,

With the switch open you should be measuring 5V on the option input.

Could you repeat the test, but measure from the board itself, rather than through the molex plug? The easiest way is to measure right from the back-side of the board where the molex receptacle is soldered in.

Of course- when you do this, be careful to not short out the board when the power is connected. Depending on where you have the MJLJ installed you may want to pull it out of the car and power it up on the bench with a 9V battery.

Let us know what you find out-

Thanks Brent,
I didn't get notified of your latest response automatically so I'm a little late getting back to you on this. The test you suggest will definitely be a pull the unit out job as the molex plug is on the far, and difficult to access, side of the MJLJ. I'll get back to you on it as soon as I can do the testing.
I had kind of expected that the switch should have 5 volts across it. I think that this may be a case of the molex pin not making contact with the plug for some reason. Thanks again for your attention to this.

Hello-

I figured it was buried inside. Definitely bench test it for convenience!

Hi Brent,
I got the MJLJ out for a while this morning and tested it. Everything works 100% on the bench so it must be a wiring problem in the car. After re-installing the unit in the car I tested the option switch and it still doesn't work. So as I said above it has to be the wiring in the car. The weather is too damp to do much on it today so I will have to get back to it later.Thanks for your help.

Hello all,
In case anyone wants to know what was wrong; I found the problem this evening. When I wired the switch I grounded it directly to the mounting screw on the car's body. This caused the trouble. The circuit didn't see this as ground. The solution was running a separate wire directly to the common grounding point where all other MJLJ components ground. Problem solved. Thanks for your help Brent.

Easy fix in the end then. I never thought of that tobe honest. Glad you got it sorted out.

Hi,

Was the original grounding point an actual ground location, albeit a poor one, or was it an insulated connection?

In any case, please try this: monitor the software with the switch in the "open" position to ensure the Ignition Maps still do not spontaneously change.

How long is the wire running to the switch?

Brent,
Total length from MJLJ to switch and from switch to ground is now about 8 feet (2.4 m). The original ground point was a stud on a dash defrost vent. Apparently there were too many bolted connections between that point and the MJLJ to give a consistently good ground path.
The only time I have seen the maps spontateously switch was when the switch was closed. Open circuit has always been OK.
I just checked last night's datalog everything worked 100%
Again thanks for all the help.