Alfa Romeo Forums banner
1 - 11 of 11 Posts

·
Premium Member
Joined
·
15,013 Posts
Discussion Starter · #1 ·
I have an intermittent problem with the speedometer in my 84/85 GTV6. The symptom is that it reads correctly up to a certain speed (which varies from day to day or from minute to minute) and exceeding that speed causes the needle to flop to zero. I started testing today and I found something interesting - The speedometer head draws more current as it indicates higher speeds and it also has a minimum operating voltage that also varies with indicated speed.
For instance at 70 mph it draws 100mA and it requires at least 6.1 volts. at 120 mph it requires at least 11.5 volts and at 140 mph it draws 160 mA and requires 12.4 volts. If the voltage at the speedometer is say 11.5 volts then the reading will peg at 120 even as you go faster.

The speedometer is powered from fuse #7. Fuses 6, 7 & 8 are powered through the ignition switch which is powered from fuse #2. In my case I got a 2 volt drop through the ignition switch when it is passing about 5 amps today and I suspect it is sometimes higher and that is causing the speedometer problems.

Has anyone successfully cleaned the contacts in a GTV6 ignition switch?
 

·
Premium Member
Joined
·
15,013 Posts
Discussion Starter · #2 ·
Added cntrol power relay

So, I had a 2 volt drop across the ignition switch which carries the current for everything that is fed from fuses 6-8 and have power that is only available when the ignition switch is turned on. This includes instruments, ignition, FI, fuel pump, windshield wipers,....

I decided to install a relay to take the load off the switch. Now the ignition switch only supplies milliamps to the relay coil and the load current goes through the relay contacts. My defroster does not work so I just rewired the relay for it.

The results are impressive. My windshield wipers run faster, my warning lights are brighter and my speedometer works properly.
 

·
Moderator
1991 164L
Joined
·
27,915 Posts
Relays are the answer aren't they.
 

·
Premium Member
Joined
·
15,013 Posts
Discussion Starter · #4 ·
Relays are the answer aren't they.
More and more so as the original switches are near the end of their design life. I first used the original defroster realy and I had almost 1 volt drop across the contacts when it was loaded. I then tried several new relays and they gave about 0.4 volts drop, so even relays may need replacing after a while if optimum performance is required.
 

·
Premium Member
Joined
·
15,013 Posts
Discussion Starter · #6 · (Edited)
No photos, it is back together.

If you want to re-use the defroster relay:

Un-hook the fuse box. It hangs from a plastic bracket on the left with a U shaped groove. Lift the fuse box on the left side until it un-hooks from the bracket. Then pull the fuse box to the left so that the plastic pin on the right comes out of the hole in the metal bracket.

Prise out the defogger switch from the dash and separate it from the connector. Make up a short jumper with two 1/4" flat spade connectors. Push the spade ends into the two female connectors that are close together and have a brown/black and black wires going to them

Find the defroster relay - it is the third from the left when looking from the front. At the back of the relay you will see the wires going to it. One pin has two pink wires. One is 12 volts in and the other is 12 volts to the next relay in the daisy chain. you have to remove this 12V from the defroster relay and continue the feed to the next relay. So, looking it it from the rear, where the wiring is, cut the pink wire that is coming from the right, close to the defroster relay. Then cut the pink wire from this relay that goes to the relay to its left, close to the relay on the left. Now solder the pink wire from the relay on the right to the pink wire from the relay on the left. You should then have a free pink wire from the defroster relay.

The defroster relay has a thick black wire going to it. Cut this wire several inches from the relay.

Look at the wires going to the terminals of fuses 6, 7 & 8 and identify the thick brown wire. Cut this wire several inches from the fuse terminal.

Solder the black wire coming from the relay to the brown wire going to the fuse terminal.

Solder the end of the brown wire that is coming from the dash to the end of the free pink wire.

Test it. Turn the ignition on. The defroster relay should click and you should have 12 volts on fuses 6, 7 & 8.

PM me if you have any questions and I will give you my phone number.
 

·
Registered
Joined
·
2,393 Posts
Now if your defroster works and you don't want to sacrifice that functionality, I suppose it wouldn't be THAT hard to install a fresh relay under the dash. Some basic DID rail fabrication, and drawing some direct 12v from the firewall through the relay to the fuse terminals with a new chassis ground to the bundle attached with the dashboard mounting bracket on the driver's side, should still get you there. Then you just want to pull the wire that went from the ignition switch to the fuses (the pink one?) to now trigger the relay.
Correct?
 

·
Registered
Joined
·
3,548 Posts
Well I'll be.... and I'm a big believer in relays, too, but that is some kind of results, Ed. Just goes to show how much resistance builds up over time on those ignition switch contacts.

If we do it though, I got a couple of standard relays and sockets with wire pigtails on hand, and we'll just cable-tie it there under the dash next to the steering column. We put so much work into that fuse box on Mike's car, I don't have the heart to snip wires and solder back there! :surprise:
 

·
Registered
Joined
·
2,393 Posts
OK, so if I wanted to keep my defroster active...

The brown wire coming from under the dash that feeds into the 6-7-8 terminals is from the ignition switch, which will now be the trigger wire for the relay? Where would I draw 12v? It seems I could just add a new ground wire to the bundle on the dash mount bracket by the driver's left knee.
 

·
Registered
Joined
·
3,548 Posts
I looked over the wiring diagram, and it's not difficult. The big red wire is the 12VDC feed to the ignition switch. The big brown lead takes the power out to fuses 6,7,& 8 as has been said. All we need is a switched 12 VDC lead to energize the relay (across 85 and 86), and bingo we got it. It looks like maybe the purple lead to the courtesy light timer might be the best choice, since it gets power when you switch the key on. And we can ground the relay about anywhere down there, even on the rail running above the fuse box.

I'm going to try it on Mike's car, maybe next weekend when he gets home from school. I ordered some Posi-Taps to use on the big gage leads. I think I'll leave the leads uncut, and just use the new relay in parallel with the ignition switch. Anybody see a problem with that?
 

·
Registered
Joined
·
1 Posts
Added cntrol power relay

So, I had a 2 volt drop across the ignition switch which carries the current for everything that is fed from fuses 6-8 and have power that is only available when the ignition switch is turned on. This includes instruments, ignition, FI, fuel pump, windshield wipers,....

I decided to install a relay to take the load off the switch. Now the ignition switch only supplies milliamps to the relay coil and the load current goes through the relay contacts. My defroster does not work so I just rewired the relay for it.

The results are impressive. My windshield wipers run faster, my warning lights are brighter and my speedometer works properly.
Hi
Im new to 116 GTV, I don't really follow electrics so in as simple terms as possible so I don't cause any electrical harm, could you tell me exactly how to put a relay around ignition. Switch to lose the voltage drop? I've read brown wire to fuse box, disconnect and use as live feed to relay, then getting that to switched feeds on fuse box is a mystery. So what relay terminals to what fuse box terminals. Really want wipers and nearside window to speed up!
Thanks
Ian
1983 UK GTV6
 
1 - 11 of 11 Posts
Top