I've got a 1986 740 Turbo and I put in a 1987 Yazaki cluster with the old 1986 speedo in it. All gauges work except voltmeter barely moves, hangs in red. The wiring on the back looks nearly identical! True, the 87' blue circuit board is different, but very close. (for example, coolant gauges are made and wired different...)

From my research, it looks like a voltmeter just needs + (positive) source-- which it has in this case.

I did try the old 1986 voltmeter instead and the results were the same. So I know it's not the gauge. My battery is new last year and the old cluster voltmeter was working fine.

Any ideas for me out there??

Thanks, DaN

Here's one site with lots of volvo info: (other stuff too)

https://blarf.homeip.net/greenbook/gallery/bymdel/
https://blarf.homeip.net/greenbook/gallery/bysection/39

There's lostsa stuff there different Volvo models and years.

Find out the number for your model and year for the Greenbook Wiring Diagram.

The 89 740 is:

TP 3183/1
Section 3(39)
Wiring Diagram
740 1989

Volvo Service Manual
Fault tracing
Repairs
Maintenance

Maybe you can find your exact manual on the web.
It shows you component locations, and exact harness/connector details etc.
Chilton's and the other dimestore manuals don't give you enough info.

Thanks Bill - a little gold mine of manuals you found

The first url didn't work for me, but this variation did:
https://blarf.homeip.net/greenbook/gallery/

Firefox said don't trust site, but so far it's been worth making the security exception.

Hi Dan,


I'd cleanup the piggy back red wire at the battery.

Bill

Thanks Bill - I'll check my connections at battery - although I'm skeptical the battery connection would suddenly go bad, I hope it's this simple... - I'll also pull the cluster out again and recheck all the screws I had to remove and re-tighten.

Follow-up: Car hesitated a little on start-up today, got me worried. Returned old cluster to car - Voltmeter is reading lower than usual! Damn... the problem is not the gauge or cluster compatibility. (the original problem was actually a dying coolant gauge)

Update:

1. Piggy-back power cable at battery did have turquoise corrosion and copper terminal-ring was on the verge of breaking off from 25 years of stress. Cut wire back and replaced with new ring terminal-- Voltmeter where it should be (more or less). Thanks Bill!

2. I've concluded the 1986 cluster is *not* compatible if one wants to keep the 1986 speedo (my objective) because the circuit board and a few gauges are revised. Swap should work fine if it's simply plug 'n play as both accept the same connectors to cluster.

However, gauge to gauge replacement is frustrating. The coolant gauge on 87' is four terminals instead of 86's three. Looks like 87' coolant gauge also has a voltage stabilizer unlike the 86'.

Speedo on '86 worked in '87 but it lacks an extra screw terminal (center of guage) that likely makes an incomplete circuit that caused the voltmeter and the warning lights (at start-up) not function.

Gauges individually that are identical:

Voltmeter

Clock

Turbo boost

Gas


Unsure about tachometer compatibility.

This concludes this discussion with myself...

Hi Dan,
I have an '84 760 turbo that I'm having similar gauge issues with and I also have an extra '87 cluster that I tried in the car but the voltmeter didn't work. Looking at the back of the '87 cluster it doesn't have a voltage stabilizer for the gas and temp gauge like the '84 and maybe '85 and '86 have. I guess I'm going to order one from the dealer for mine since the symptoms are pointing to that. I already went and replaced the terminals at the battery.

Dave

Hi Dave--

I hadn't considered the dealer option! Just assumed gauge was out of production -- let me know if you do get a new replacement.

I think in my brickboard searches I recall your thread about the temp gauge.

Re voltage stabilizer -- I don't think the '86 temp gauge had one, but the gas gauge does. The '87 was improved with one attached at the gauge's circuit board (seen when removed from cluster; same for gas gauge)

What's frustrating is my Haynes wiring diagram doesn't help because it diagrams the general path and not the specific version of the Yazaki circuit board. Yazaki seemed very flexible about modifications and improvements, which is good for Volvo and them. But not so good when trying to repair.

My original cluster is 19860321 (1986-03-21) dated, my '87 cluster is 19861016 dated -- so in seven months the changes were made.

Hi again Dan,

OK on fixing that pesky piggyback pos wire at the battery. The SOB was hard
to keep secure and I had to add bronze lockwashers.

I have the Greenbook for the 89 740 here.
The voltmeter shares the source for the Speedo pin#4, The Tach and fuel guages,
The temp guage, and most of the idiot lights.
The rheostat supplies only the dash lights, and the service idiot light.

I'd get a voltmeter and see what voltage you read at the 4 pin speedo connector
pin 4 is + and pin 3 is -
Maybe you have a lossy or missing ground somewhere.

Check that and post back.

Meanwhile there's a website with parts of the 740 greenbook Wiring diagram.
Essential for troubleshooting!
I'll try to find it.... Try the search engine here... "blarf"
I'll post back if I find it.

Bill

Hi Dan,
I got a replacement voltage stabilizer from the dealer for around $18, but when I was removing the old one from the cluster I heated the solder joints too much and melted the board. Now I don't have a good area to connect the voltage stabilizer to. The dealer says $212 list for a new board. I have a cluster from an '87, but from your previous posts this wouldn't work in my '84. Any suggestions?

Thanks,
Dave

I'm sorry to say this is getting out of my knowledge base...

Dashboard compatibility: From what I've gleaned on the internet and my own 86' dashboard is that years 1985 thru 1990 are interchangeable with same lead wire/connectors but variations in gauges within the cluster. So, yes, my best guess is that 1985 clusters and above don't work for your car. And then even if it did, it's very unlikely you couldn't re-use your speedo/odometer, you'd be stuck with a different mileage odometer.

I'm waiting for an '85 cluster to arrive in the mail, and hope to use it's temp gauge.

The best option is to find a junkyard cluster in your area or go ebay (or the classifieds here on Brickboard)

Soldering: I can't do it to save my life...

DaN

Are you talking about the rheostat?

If you pulled tracks off the board, you can solder jumper wires
back to a good part of the board, providing you can see where the original
track went.

Solder the jumper to some solid metal lug somewhere,
or even a wire in the harness.... you can't solder the plastic circuit board.

You need maybe around a 25 to 30 watt iron at most for this work.
Using too much heat will wreck stuff..

Any idea what the gray plastic plug with 4 wires that connects just behind the speedo on the back of the cluster? It's a harness plug a few inches long and resembles a factory amp plug connector (which I no longer use on the car since I have an aftermarket stereo). Just wondering why this would connect to the back of the cluster?

Thanks,
Dave

The rheostat is ok, but the part of the board where the voltage stabilizer connects to is what I damaged. Good point about the soldering iron, I will pick up a lower wattage iron for when I place the jumper wires. $200 is more than I care to spend just for a circuit board.

Thanks!
Dave