unloading the ignition switch?

EricH

EricH

Eric Hamilton
Moderator
I was thinking about rlingren's recent tale of woe involving a burned ignition switch... and the pain that a burned ignition switch wire causes me... and I find myself wondering whether there's a better way.

There's a blue-black wire from the ignition switch to the fusebox that carries all of the switched power for accessories - lights, wipers, instruments, and so forth. Suppose I were to disconnect the blue-black wire at the fusebox, use it to control a relay instead? Then I could run a suitable heavy wire from the battery to that relay, and thence to the fusebox - and the ignition switch would never have to carry more than the tiny current needed to activate the relay.

Anyone ever tried something like this? Any reason why it shouldn't work?

The '74 already has a relay for the starter circuit; it's controlled by the seatbelt interlock thingummie by the glovebox. Both input terminals of the relay are powered from the ignition switch though, so the full current draw of the solenoid still comes through the ignition switch. It would be easy enough to change that as well: run one more wire direct from the battery to the relay's switched input in place of the wire from the ignition switch, leave the ignition switch controlling the relay.
 
After my gut-wrenching experience with replacing the ignition switch last spring ( I burned out 2 brand-new but cheap replacements variously stranding me at night at the local WalMart parking lot and 25 miles away from home at a car-wash), it's certainly worth a try.:hmm: With your success you could write up a thing on the mod that would join the collective conciousness alongside the Brown Wire Mod and the Headlight Relay Mod. Come to think of it, your idea could replace the BWM.:2c:
 
I'm going to do this and I have all the parts to do it but haven't gotten around to it. I have a pair of ignition switch connectors that I'm putting together so that a bank of relays, one for each ignition circuit, plugs inline between the ignition switch connectors. Also, I'm going to have a relay that is activated by the key switch so I have an accessory circuit that turns off when removing the key. I also have the headlights relayed so this is probably way overkill but that's okay.
 
My '85 started cutting out for brief periods while driving and it turned out the be the ignition switch. After I cleaned the switch contacts I did just what you are proposing, inserted a relay to offload the ignition switch.


I'm not familiar with the wiring diagram for the '74, but on the '85 the wire for the alternator light taps off the connector for the ignition switch. You have to insert the relay upstream of this connection. The wire for the alternator light must be connected the same terminal of the relay as your connection to the fuse box. Practically speaking, this means you have to interrupt the circuit at the connector for the ignition switch, not where it enters the fuse box. If you interrupt the circuit at the fuse box, the alternator light will be connected to the coil side of the relay, not the contact side, with the interesting effect that after you turn off the ignition the alternator will back-feed your relay and the engine will never stop. The '74 might be different.


For the starter relay, I think what you are suggesting would work fine. If it were me, I'd rather install one of the hard start relays discussed in this thread. Both ways will offload the ignition switch, but the hard start relay has the potential for less voltage drop at the starter solenoid.
 
VW has used a solution using a relay on their cars for many years. It is referred to as the load reduction relay.

Basically all of the primary loads, heater fan, defroster, lights, wipers and so on are run off of this relay under normal use (the run position of the ignition switch) thus off loading those direct loads from the ignition switch. When the key is turned to the start position, power is cut to the relay and therefor those accessories to provide maximum power to the starter.

This would seem to be a good tactic for our cars as well. I believe VW gets the function in the ignition switch, our ignition switches are not set up this way. However we could add two relays to get the same effect. One relay controls power flow to the second relay and the second relay controls power flow to the accessories. The first relay's coil is powered by the start position of the ignition switch and the second relay's coil is powered by the "on/run" position of the ignition switch.

I have included a wiring schematic I believe would serve:

Loadreductionrelay_1.jpg


The current flow is as follows: Power comes into relay A 30 terminal, it then flows out of the 87a terminal (this type of relay has continuity from 30 to 87a until power is applied to the coil) to the 30 terminal of relay B. If there is power from the ignition switch to the 85 terminal of relay B then the relay will switch power to the 87 terminal to power the accessories.

If power is applied to relay A's 85 terminal from the start position of the ignition switch, it will cut power to relay B's power circuit giving the load reduction function we want.

I hope that is clear.
 
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Another way this might be accomplished is to ground the relay coil through the starter solenoid. That way when the starter solenoid is activated there will be power on both sides of the accessory relay preventing it from turning on.
 
Did this about five years ago and have never looked back. Works like a charm and takes the heavy loads off of the ignition switch.

The bypass relay that I installed is a 50 amp relay and came from a Porsche 944 since thats what I have access to at my work. In the picture it's the large silver relay next to the (White) interior light dimming relay. Above the fuse board (right of picture) is a soldered heat shrunk bundle of wires that came from the battery, thus eliminating the problematic large plastic connector. That bundle feeds the bypass relay which supplies direct battery power to the fuse/relay board and all the Terminal 15 or ignition controlled circuits.

With this modification the only thing the ignition switch does is supply power to the instrument cluster, the starter solenoid, and trigger the bypass relay which then supplies direct battery power to the fuse/relay board. This eliminates the need for the brown wire mod, keeps the wiring simpler and the current path shorter. The end result is that I have brighter lights, a faster wiper motor,a faster blower motor and a volt meter that never goes below above half with everything on.

The extra relays below the bypass relay are a headlight low beam relay (the late models already have a headlight high beam relay) and a extra radiator fan relay. I was just using the spare relay bases since this is a non A/C car



P1010001-2.jpg
 
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That's a bummer to hear on the '74 set up...

Do you know off-hand which wire color from the ignition switch is the primary feed?

Guess the factory relay was not intended for power load purposes, but more so to tie in with the seatbelt interlock.
 
Dayton Tom said:
Do you know off-hand which wire color from the ignition switch is the primary feed?

Guess the factory relay was not intended for power load purposes, but more so to tie in with the seatbelt interlock.
Click to expand...

Yep - that's the only reason it's there. The feed from the ignition switch to the relay is orange, as is the switched output from relay to starter.
 
Anyone else do this yet?

I think Kmead has the right idea and this is what I did as well. Worked like a charm and took the current/heat out of the ignition switch. I've had good results and have been running the load reduction relay for about five years now:nod:
Rolf Grumme.
 
Hi, i am trying to do the same mod on my 1987 1500 but i think the wire which goes to the fuse box for the heater wipers light etc is red and black.If so how do i connect a relay in and what wiring goes where

Sorry but i am a bit of a novice to electrics

Thanks Shaun:dunce:
 
To Ng_randolph- I know this thread is a little old, but my '82 has started cutting out also. It acts like someone switched the engine off and I have to re-start it. Is that what yours did? This problem is, in fact, why I'm on the forum this morning. BTW I have a new Yugo ignition switch I installed about 2 years ago, and I've done the Brown wire mod. The problem only occurred twice, and the first time I thought I was just crazy. Now I'm starting to become convinced....
 
jasco said:
To Ng_randolph- I know this thread is a little old, but my '82 has started cutting out also. It acts like someone switched the engine off and I have to re-start it. Is that what yours did? This problem is, in fact, why I'm on the forum this morning. BTW I have a new Yugo ignition switch I installed about 2 years ago, and I've done the Brown wire mod. The problem only occurred twice, and the first time I thought I was just crazy. Now I'm starting to become convinced....
Click to expand...
That is exactly what mine did. Cut out very briefly, then restarted.

I removed the ignition switch as described in this Wiki article. I picked it apart and cleaned the contacts. The electrical part of the ignition switch is riveted together. After I took mine apart, is used two 16 mm long M1.6*0.35 screws (McMaster part number 91800A011) and nuts (McMaster part number 91828A006) to put it back together. I then installed a relay to off-load the contacts in the ignition switch.

You might also consider installing relays for the headlights (offloads both the ignition switch and the headlight switch and provides higher voltage to the headlights) and a "hard start relay" (offloads the ignition switch and provides higher voltage to the starter solenoid; search for it on this forum).
 
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I know this thread has been dead for a while, but I would like to unload my ignition switch and I see Rolf's solution of putting relay from the ignition switch to the fuse box. He mentioned it was an orange wire, but it also appears his is the newer spade version of the fuse box. I have an '83 and therefore the older fuse box. The wiring diagram for an '81 (presumably same as '83) shows a Blue/Black wire going from the C18 connector near the ignition switch to the A and B fuses (to other accessory relays, indicator gauges, dash panel, fan blower, etc.).

Does anyone think it would it be a problem putting a relay in line with that Blue/Black wire between the ignition switch and fuse box? Or is there anything on that line that would have any issue with it being on a relay? That way only the instrument cluster, starter and headlights run through the ignition switch.
 
EricH said:
I was thinking about rlingren's recent tale of woe involving a burned ignition switch... and the pain that a burned ignition switch wire causes me... and I find myself wondering whether there's a better way.

There's a blue-black wire from the ignition switch to the fusebox that carries all of the switched power for accessories - lights, wipers, instruments, and so forth. Suppose I were to disconnect the blue-black wire at the fusebox, use it to control a relay instead? Then I could run a suitable heavy wire from the battery to that relay, and thence to the fusebox - and the ignition switch would never have to carry more than the tiny current needed to activate the relay.

Anyone ever tried something like this? Any reason why it shouldn't work?

The '74 already has a relay for the starter circuit; it's controlled by the seatbelt interlock thingummie by the glovebox. Both input terminals of the relay are powered from the ignition switch though, so the full current draw of the solenoid still comes through the ignition switch. It would be easy enough to change that as well: run one more wire direct from the battery to the relay's switched input in place of the wire from the ignition switch, leave the ignition switch controlling the relay.
Click to expand...
I did something similar but different with my Blue '74. I ran an 8 gauge wire from the battery to an insulated terminal behind the "bertone" plate. From there I ran a power wire to the main lead on the starter relay, I didn't do the blue/black wire, but I did run a new lead as a jumper of sorts to both the spade terminal brown wire junction behind the HVAC, and the unswitched fuses on the box. The headlights got the relay treatment too, and I stopped there since IMO the main items now were covered
.20140216_152726.jpg20140216_152735.jpg20140208_161313.jpg20140216_152802.jpg
 
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