I have just picked up a Yellow 92 MR2 GT, Veilside widebody and "VERBO" on the plates and it has a few gremlins under the bonnet - the owner told me there was a short and his mechanic just bypassed it - hmmmm. The speedo and tacho where not working.
First I checked all the blade fuses, none of them where blown in the three different fuse boxes. All lights and other functions work.
When I first opened up the under dash area I found 2 plug and play ignition harness adaptors, plugged into each other, one was for a old alarm system that was still installed and the other was for the HKS turbo timer fitted on the steering column. Neither where plugged into the original harness. Add to this I found those stupid scotch locks used here and there and the odd bit of speaker wire....
First thing I did was chop the alarm out, solder up all the stupid scotch lock connections, and then plugged the PNP adaptor for the TT in and fired her up. The turbo timer works and there is no warning lights on all of the dash are out except for a small one that appears after a while of short start and stop driving - its a little red light that looks like a fan some little waves and the engine symbol - I have identified this as the inter cooler fan, need to look into this some more.
This is where it gets interesting - the Turbo Timer has a rev counter built into it that displays the revs, and this is working fine. The speedo when your sitting on 80 kph (assumed as that was what the speed limit was and maintaining speed with other cars) would read consistently on 25 kph. The standard Tacho reads 0.
Anyway I took the car to pedders to get a check over and ended up getting some ball joints replaced and a wheel alignment. On the test drive the P/S light came up and has stayed on ever since. Was working fine for me before hand. Checked fluid and belts, all seem ok. I wonder if this has something to do with my other problems? Ether that or a sensor or wiring has been damaged that finally gave way...
Now has anyone ever put a shift light in? And can confirm the tacho gauge wire, colour, location etc? I am yet to confirm if the speedo is mech or elec, its so busy in the engine bay - research tells me that the 92 had a mechanical unit, but I cannot confirm, need to get some mirrors in there.
If the tacho on the TT is working but tacho on the car isn't you either have a faulty tacho or the wiring has been severed to the tachometer. It is VERY likely that the TT tacho will be reading its RPM source from the same place as the tacho on the dash should be, and thats the ignition coil negative from memory (which has been getting hazy lately).
I've seen similar issues with the speedometer before, see if you are electrical or cable driven. Quite often with the electrical speedos I've seen the speedo reading low due to failed capacitors (think its caps, could be resistors though, as I said, hazy memory, I did one repair once on one cluster) on the speedometer circuitry in the dash cluster. If you google around you should be able to find a writeup regarding this somewhere.
Thanks for your help. Its a JDM import, Turbo, not sure if its a Rev 2 or not, I couldn't find a plate on it saying whether its gen 1 or 2. I have found a explanation on how to tell the difference, I will have a look tonight, as well as susing out if it has a mech or elec speedo or not - I hope its electric.
Yeah I'm thinking the same thing - the TT has a speed display on it as well, so I reckon they have run the wires in paralell, then its buggered up some how.
James I was thinking the same thing about the capacitors, just want to make sure I have the right wires first before I go down that route
Maybe its a non turbo and someone converted it to turbo
And did a shonky job on the wiring
Sounds like some wanker has been wiring it if there are scotch locks everywhere
Tacho signal comes from ignitor
Check the speed sensor on gbox to make sure it has ground and 12v power
It's a three pin plug on the gbox. Usually black oval shape
Some of these have a cable for speedo
So check that inner cable isn't broken
One other thing I remember from many years ago
Some mr2 gboxes had speedo issues when doing conversions
The special mechanical speedo drive was very hard to get
I think turbo boxes where electric speedo
Non turbo where cable
So if u fit turbo box and turbo engine to non turbo mr2
U had to buy a different mechanical drive that its turbo box
These were very hard to find second hand
Anyway just a thought since its been dodged up so much it might be a non turb
That's been converted
So the plot thickens. Dumbass, you are right about wankers and there wiring...
Decided to bite the bullet and pull the gauge cluster out over the weekend. Found the middle plug on the cluster, 7th wire from the left, a green one had been cut and run in series to the dimmer switch? And the original dimmer switch plug has vanished, and they have just soldered the wires directly onto the potentimometer. From here this supplys the dimmer signal to the boost gauge on the A pillar.
Thinking I'm getting somewhere, I cut the join and soldered the green wire back together - before doing so, I confirmed that this wire only supplys power to two halogen bulbs on the cluster - forgot to whack a multimeter on there as I got a little excited with my find.
Anyway put her back together and fired her up, and the only thing that has changed is now the back light on the boost gauge does not work when you turn the cars lights on. I am thinking putting this wire back on as it may be the only way of dimming the dash lights. Still a very strange way to go about it - if they couldn't get the right plug, why didnt they just change it? Not that hard to solder to the terminals and have an inline plug...
I can confirm that this car is not converted and is a genuine GT JDM import. Its definitly a gen 2 as it has a elec speedo, as their was no cable input at the back of the speedo.
you'll need to find where they spliced/connected the TT into the loom for the speed and rev signals.
if you get the PS light and the cat temp light come on at the same time that usually mean's there's a charge issue (battery/alt) however with the dodgy wiring it may just be the cluster not getting the correct volatge signals and thinking the alt isn't charging.
Yeah thats what I have been trying to find, its strange cause when I put the multimeter on the TT to find the tacho signal, I found one of the three wires was reading 4.4VDC, but when I reved the engine, the value did not change.
Any way going to give her a service and pull it apart again this weekend, and wire up the boost gauge properly then chase the wires back to the engine bay and confirm if they have been cut at the ecu
I replaced the two capacitors on the back of the tacho even though they didnt look dodgey, and hey presto, the tachometer now works!
Also the P/S is now gone, as soon as I bought the parts to flush the system it decided to turn off! But the belt started squeeling at full lock - easy fix
Whilst I was at it, I pulled the speedo out to have a look, and found a 100uf 25VDC capacitor had one of its legs rusted off. So I replaced this as well - but this is where my luck turned - then had a case of the butter fingers and managed to drop the speedo from the table where I was working onto the hard tiles. This cracked the edge of the pcb board off. So I then spent the next half hour carefully scraping the coating off the board, and bypassing the broken solder tracks. I tested it with my multimeter and I had a good circuit accross all of my repairs.
Whacked her back in the car and the speedo is doing the exact same thing as before. My first thought was that the speed sensor could be playing up, however the speed displayed on the TT is accurate enough that I am maintaining speed with traffic. As Jonathan has said I need to find where
Whilst I had the cluster out I reconnected the dimming circuit back up and now the boost gauge lighting is working again, and I have control of the brightness of my cluster instead of just going to max brightness.
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92 SW20 MR2 Tacho Speedo issues
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