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Recently, Nevyn72 removed his NB SE's oil pressure gauge and fitted a boost gauge in it's place. Following this, he then wired up an oil pressure warning light, taking signal from the standard gauge's terminals on the instrument cluster's circuit board to one of the unused cluster lamps, like this:



When I was reading through his thread again this morning, I wondered if this would still work if the stock opg remained fitted and functional. I don't particularly need this myself, but curiosity won out and I removed my instrument panel and wired it up the same and plugged it back in. It kind of worked, but the warning light bulb does not completely go out once the engine is started. It dims, but remains partially lit. Maybe some sort of current within the gauge that passes through? I didn't have any time to do any more experimentation.

If anyone with any electrical knowledge can suggest what is going on here and maybe if some sort of resistor on one of the wires might fix this?

I know there's various versions of the Miata.net opg mod and ways of fitting a seperate warning light via dual sensors (I already have a seperate VDO opg/sensor fitted), but if this method could be made to work, this could be a simple and cheap fix for a warning light for many people.

I realise I could simply reroute the stock opg wire from the sensor directly to the light fitting instead of the gauge and it would work and the stock gauge would still "appear" normal, but the idea was to see if there was a way to keep the gauge functional (as much as it is) while simply adding the light without too much fuss or expenditure.

I'll be experimenting with it over the next few days just for the heck of it. Maybe I'll even accidentally stumble on a fix. If anyone wants to give some educated advice and/or suggestions, please feel free...

OK, so other tasks taken over, so have to give this up for now. Removed the wires & plugged the panel back in ... but now I have no instrument panel warning lights at all!! Instrument lights all work, the room light works, and the car starts ok. Must have blown a fuse somewhere!! Damn!! Too dark now, so has to wait for tomorrow.

... new cry for assistance - if anyone has had this happen before - losing only the dash warning lights ... let me know which fuse or what else it was that fixed it ...

EDIT: ok just thought to go out and start the car again and check if the instruments are actually working - No!! Started car and OPG, Tacho no response! Dash lights come on ok with the lights, but no warning lights & instruments not functioning.

What have I done?

Have you got another instrument cluster to try?

From memory looking at the wiring diagrams the cluster has a microcontroller inside, any chance you could have fried it?

No spare cluster unfortunately. Hope it's not something that serious! Mine has the NB8B cluster fitted, not the standard 8A cluster. I've obviously shorted something with my experiment. Checked most of the fuses under the dash, but not all.

Fingers crossed for you!

Thanks ...

Hmmm ... not looking good. Went out after dinner and tested the fuses with my line tester and all appear fine. Bit hard focusing on them properly, still getting used to my new multi focal glasses, so may have missed one or two. Will check properly again tomorrow.

Anyone know if any other fuses/relays anywhere else could affect the instruments? Had a look online and a lot about the earthing points but nothing I could find on the relays.

The owners manual describes what fuses affect dash lights. I might suggest reversing mods. Also best to do this in daylight or with headtorch

Ironically it was after reversing the mod that I've blown something Hopefully daylight will present a more promising outcome ...

Are you sure the connectors are pushed fully and properly into the back of the cluster?

The wiring contacts are on a flexible sheet attached to the back of the cluster, have been folded over or creased?

I pulled the cluster out to see if I could see anything obvious and then plugged it back in. All the bulbs are still good and nothing on the circuit jumps out. The odo doesn't display either.

I'll check the earthing points today under the bonnet that are mentioned on other threads, but would be a huge coincidence ...

The next step would be check if it's something in the oil gauge itself, this is the wiring you directly effected by the mod so it might be internal in the gauge unit.

Remove the cluster, remove the front plate of the cluster, undo the three screws that secure the oil gauge from the rear and remove the oil gauge.
Plug it all back in and test to see if it works......
If not then attach the light to the two connections (with the gauge removed) and test again.

One thought, when you attached the light the first time, was the connection to the ignition circuit completely isolated?
There are exposed connections to other circuits close to that point where a short may have occurred......

Thanks Nevyn ... I'd been outside checking every fuse and relay. They were all fine.

I read your post and was about to follow your suggestion and noticed this:



Followed the circuit and it is an ignition track, so would be cutting power.

First a coffee, then try to delicately solder a small piece of wire across the tear.

Hopefully it hasn't caused further damage.

Not pretty ....



But TADAA!! ...





I reckon I must have damaged the circuit while fiddling around trying to get the loom plug back in. I've shielded my join so that it doesn't short anywhere. Still a bit surprised that no fuse had blown anywhere ...

Yeah! At least the cluster was able to be saved.

I suspect there was a short somewhere with the wiring for the globe you were testing..... Not surprising a fuse didn't blow, that printed circuit is a lot lighter than the main ignition fuse!

What is the wire for that you have running from the main backlighting globe fitting?