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Over the past few day I've had some problems with the tacho in my 1979 rx7. Initially just sat at around 5k when idling and then basically redlined whenever I was driving. Today i was driving and the needle was all over the shop. Then I got oil, battery and fuel warning lights.

Battery seems to be fine, car has half a tank of petrol and the oil is topped up (although it could be oil pressure). Also, there has been no noticeable change in performance and the car runs really well! Probably also worth noting that the car is basically 100% stock, so i doubt this comes down to dodgy modifications.

Just wondering if anyone has any idea what this could be? Is it something i could fix myself or do i need to visit a mechanic?

Thanks in advance

On the nearside (LHS) inner wing near the bulkhead are a couple of relays. The outer one of these - the 'U' shaped one in a domed metal cap puts the warning lights up when you turn ignition on.......it does on the S3 anyway.

The tacho is linked in somehow as well.

I would look at this relay as a first step. You can prise the can open and maybe clean up the contacts but a replacement might be easier if you can find one.

Second step will be to check all wiring earths. Finding these will be fun. Look for black wires (from memory) grouped onto earth studs at different places.

Hope that helps.

Codge

Are you running the stock external voltage regulator for a '79? I'd check what she's pumping out for a start. The tachometer is driven direct off the trailing coil so shouldn't be anything directly with the warning lights.

Thanks for your advice guys!

I'm struggling to find the correct relays, are they inside the engine bay or like in the passenger footwell? Also, if it was a ground termination issue would i have to pull out the instrument panel?

Not sure about the voltage regulator, I'll have to check!

Sorry for my lack of mechanical know how :/

Thanks again

On an S1 the tacho and voltmeter are combined so when the key is at ACC position it'll tell you voltage and when engine is running it switches to revs. Thinking about what you said, it doesn't sound like its switching over.

I think Tim's correct, the S1 uses a regulator.

I have only experienced this problem on S3's which are somehow different.

The relay on S3 is inside the engine bay, on the wing just behind the hot start motor/cable thingy.

Earths? Dash out only as last resort. You need a wiring diagram, preferably a schematic with an item location list.

The normal Haynes manual is a soup of mixed models and only up to S2; US LHD, California Emissions Spec, together with UK RHD cars......A right mess!

Have a look on here. Might be an S1 Diagram.