Recently, the cruise control and radio went out on my 85 240. The fuses are fine, as the other instruments on those fuses function normally. Additionally, my wipers have been going haywire; they will not turn off once turned on, and they will run until I turn the car off or for a period of time until they randomly stop.

Is it possible these strange electric issues, appearing at the same time, are interrelated? Or is it just coincidence that they each failed simultaneously?

 

a flakey ground can cause circuits to intermingle like that.

but, a 1985 is in the midst of Volvo's 'biodegradable wiring' era, where the insulation on the individual wiring inside the outer sheaths is prone to crumbling and cracking with age, which can cause all sorts of hard to diagnose random behavior, and the more the wiring is handled, the worst it gets. the main engine harness is *usually* the first to go due to the heat, but all wiring in the car is suspsect... these years run from circa 82 or 83 to mid year 87.

side note, Mercedes had the same problem from 93 to circa 98, but dealers were more proactive on replacing at least engine harnesses... virtually every 93-95 E class still on the road probably has had its harnesses replaced

 

I finally got a harness from Dave Barton, any tips on replacing? Looks like it'd be easier with intake manifold of.. I may go ahead and take parts of the intake out anyway, need to clean the throttle body and PCV box anyway.

 

get a intake manifold gasket if you remove that, and a throttle body gasket if you remoove the throttle body.

otherwise, I laid the new harness out over the the engine paralleling the old, started by unplugging the part that is inside under the glovebox, and stuffing the new harness in its place and connecting the ECU and fuel pump relay and stuff, then proceeded to swap each connector, rolling up the old harness as I went along.

 

got the new wiring harness in; but radio still doesn't turn on. I have this receiver: https://www.crutchfield.com/S-FDGagl...DC-BT375U.html

The front console - which has the dial and buttons - pops out of the receiver. I popped it out and put my meter on the receiver with the accessories on and it is getting voltage from the battery. So would this mean the front console is dead?

I know car stereos are complex and all... but just a shot in the dark here.

 

a typical aftermarket car stereo has two power wires, one is red, thats always-on power, for the clock and station memory, the other is yellow, and thats switched power when the ignition is in I (accessory) or II (on/run), and is the power for the actual stereo.

lets see, the *factory* radio, the switched power was a yellow/black wire from fuse 1 that went to pin 2 of a 3x3 (9) pin block connector, and there was no always-on wire connected directly to the stereo, however a green wire from always-on fuse 8 ran to the antenna via pin 1 of that same 3x3 block connector..

now, aftermarket radios, I've seen some real butcher jobs, so all bets are off how it was wired. If it was done /right/ it was connected to that 3x3 block connector via an adapter. but I've seen all kinda wrong, wires cut and twisted and wrapped in scotch tape, you name it.

 

finally getting to this....

I thought my head unity was dead so i ordered another. same make - kenwood - with the same 8pin adapter. Yellow is battery wire, red is ignition wire.

The wiring is setup as pictured, with the 8 pin going through an adapter to the 6 pin stock wiring harness:


However, the new unit also won't switch on...

I am getting 12.18V at the red ignition wire with ignition on, 17.5V at the yellow battery wire with ignition off, and 20.8V at the yellow battery wire with ignition on.

Fuse #1 and #8 are good and working - or at least, the other instruments on each fuse are still working.

So that leaves me assuming the ground wire must be bad? have I overlooked anything?

 

17 and 20 volts are *WAY* too high, there shouldn't be anything above about 14.2 volts anywhere in the electrical system with the engine running.

are you sure you had your volt meter's ground/negative lead connected to a good ground when you made these measurements?

 

Yeah that somehow didn't occur to me until a bit later! my ground was bad. I re-measured and the problem is that constant power wire - it's reading 3.5-4V.

the yellow wire comes off the 8pin terminal that would power the aftermarket HU, and it connects to a blue wire that runs independent of the terminal adapters. So when the aftermarket unit was installed, they did NOT use the green wire in the original 6pin stock terminal as the constant power.

I tried probing the 6pin stock terminals for constant power (green wire, pin 1) and ignition power (yellow-black, pin 2) but my meter was giving me dumb measurements, probably due to user error. when I have everything plugged up as pictured, the issue is the yellow constant power wire.

I assume I'll need to tear my center dash open and figure out where that wire runs and why it's not getting proper voltage? If I could probe and confirm the stock green wire is getting constant 12V, I could just run a wire there?

Strangely, the ignition switch power IS wired into the original 6pin terminal - and it is getting proper power all the way to the end, at the 8pin to the HU.

 

ok, on the 240 fuse panel, on the right side of the fuse block, next to each fuse, there's 3 rows of spade lugs. the farthest/rightmost is the 'input' to the fuse, and that spade is cnnected to the left side fuse clip.

the right side fuse clip is conncted to both the left/nearest spade and the middle spade, those are the "outputs" of the fuse.

the always-on green wire is connected to fuse 8, shown as the middle spade lug. fuse 6-7-8-9-10 all get their power from a 2.5mm^2 red wire that comes off the positive terminal which is under the hood on the right fender, this wire is nominally plugged into the input of fuse 6 (6-10 inputs are all connected together inside the fuse block).

the switched yellow-black wire comes right off fuse 1, also drawn as the middle lug. fuse 1-2-3 get their power from a 4.0mm^2 yellow wire that goes from fuse 2 to the ignition switch "X" output (on in I and II), again these fuse 1-2-3 inputs are all connected together inside the fuse block.

the ground wire should come off a ground screw where the left side of the center console meets the transmission hump, via a black wire.

 

alright I officially don't know what the hell is going on with my car.

the constant 12v power is actually coming off of a coil-thing behind the brake pedal. it looks like they spliced a blue wire off a red wire to a 10A fuse that then runs to the yellow wire for the ultimate 8pin terminal that powers the radio unit.

here's a 2min video with me muddling over the wiring (excuse my terminology, I was not being precise):
(forget the part with the fuses, I was misunderstanding the input/output positions)

The constant power wire is still only running 3.5-4v where that 10A fuse is - basically where it originates behind the brake pedal, at that coil thing

looks like I have some re-wiring in my future!

 

fuses 1-2-3 input side are hard wired together inside the fuse panel, so a wire on the input row to any of them is powering all three. the wiring diagram for an 85 showed the power going in on the fuse 2 input pin.

ditto fuses 6-10, they are all wired together, so any one of them has a wire on the input side, its powering all of those fuses. I think the diagram showed that the power wire went to fuse 6 input (which is connected to fuse 7,8,9,10).

 

Right, I misunderstood in my unedited post. apologies...

but that constant power wire is definitely coming off some rando thing that it's not supposed to, at least as far as I can tell.

 

well, that green wire to the 3x3 block connector should have come right off fuse 8. it doesn't need another fuse, because fuse 8 (8 amps) is in the circuit already.

 

well that's the ticket. I de-spliced the constant power, dropped it on fuse 1 lug and it's golden! thanks pierce. you are the MAN!

 

um, per my diagram, green constant power was on fuse 8, fuse 1 was yellow/black switched power.

 

right, but I am running constant power independent of the green wire on fuse 8. constant power wire to radio wasn't going to the green wire through the wiring harnesses. that being said - will it make a difference if that independent wire is running off fuse 8 or 1? both have spade terminal 1 (output) available. independent constant power wire already has a spade terminal on it so I dropped it on one of the lugs.

thanks for your continued help as I muddle through this. i don't mean to be a PITA, but I am not ultimately using that green wire off fuse 8 in the stock 6pin terminal. or at least it appears I do not have to.

 

for whatever reason, the stereo shop didn't use one of the aftermarket METRA harnesses that has a wire for pin 1 to the original factory harness - i.e., constant power of the green wire. so they did a work-around at the coil behind the brake pedal. that failed. i just tore it open and dropped the spade onto the first available output on the fusebox.

to clean it up I need to either get a longer wire to the fuse lug or get a proper harness or otherwise get that constant power wire off the 8pin aftermarket terminal to the green wire off fuse 8.

thanks again