Good Day All, I'm new to all things electronic. I am restoring an older 1955 vehicle using a newer 2008 drive train. I've run into problem in connecting the Body Control Module ( BCM ) using the older vehicle ignition switch. The BCM is used to control, among many other systems, the charging system and cruise control operation, functions I wish to use.
The newer ignition switch, which I cannot use, powers up the BCM. I'm attempting to imitate the functions of the 2008 ignition switch using the 1955 switch along with fuses, relays and diodes.
The 2008 ignition switch had 5 contacts, being in order battery, off, accessory, run & start. The 1955 switch has 4 contacts, being batt, ignition solenoid and accessory . Further complicating is that the 1955 switch contacts battery, accessory and ignition are energized when the key is in the on position and contacts start, ignition & battery when the key is in the start position.
I have attached the schematic of the 2008 ignition switch and which shows the discrete outputs to the BCM. Also attached my schematic which attempts to imitate the 2008 outputs using the 1955 ignition switch.
I would appreciate if some members could review my schematic and comment if they think it is workable or not.

 

Interesting due to the lack of information. Most 2008 vehicles here in Australia the BCM also is part of the security. The Ignition key have transponders in them & the Ign switch reads the transponder & activates the BCM, this then sends a signal to the engine ECU to allow the engine to run.

 

Unfortunately DEBE has pointed out the big problem, which is the wireless communication exchange done for security. he key module must handshake with the BCM computer module and probably the engine control module for it all to work. aside from whatever is powered in the "OFF" position, the switch operation should be similar. The ACC is powered in both the ACC position and the run position,, disconnected during "START." In the "RUN" position, after starting both "RUN" and "Acc"are powered. And in the "OFF" position the security alarm is powered. If you do not include the portion of the modern switch that communicates with the BCM, nothing will switch on.
The big advantage of running everything thru the BCM is that when the alternator regulation portion fails, instead of a $35 alternator regulator needing to be replaced, you need a new $700 BCM that also needs to be programmed to accept your key. That costs an extra $100, BTW. (The advantage is not for you, but for the dealer)
A possible alternative is replacing it all with an off-road system that takes things back to 1965, where all of the systems were electrical and no computer modules included. BUT that is probably NOT what the TS wants.

 

Interesting due to the lack of information. Most 2008 vehicles here in Australia the BCM also is part of the security. The Ignition key have transponders in them & the Ign switch reads the transponder & activates the BCM, this then sends a signal to the engine ECU to allow the engine to run.

Thanks for looking Debe, Yes you are correct about the transponder and security system. I do not have a Theft Deterrent Module but imitated the "key in" position which I assume will trigger the BCM to send a signal to the ECM to turn off the fuel pump. I have deleted the VATS from the ECM so I hope the BCM signal will be ignored.
The engine and trans work great with no problems. Connecting a scanner to the OBDII port shows the ECM and TCM but not the BCM so it is not powered up although all 12V and ground connections are in place. I've come to the conclusion the problem is the ignition switch.
My other, more costly, solution is to buy a Dakota Digital VCM 101.

 

Unfortunately DEBE has pointed out the big problem, which is the wireless communication exchange done for security. he key module must handshake with the BCM computer module and probably the engine control module for it all to work. aside from whatever is powered in the "OFF" position, the switch operation should be similar. The ACC is powered in both the ACC position and the run position,, disconnected during "START." In the "RUN" position, after starting both "RUN" and "Acc"are powered. And in the "OFF" position the security alarm is powered. If you do not include the portion of the modern switch that communicates with the BCM, nothing will switch on.
The big advantage of running everything thru the BCM is that when the alternator regulation portion fails, instead of a $35 alternator regulator needing to be replaced, you need a new $700 BCM that also needs to be programmed to accept your key. That costs an extra $100, BTW. (The advantage is not for you, but for the dealer)
A possible alternative is replacing it all with an off-road system that takes things back to 1965, where all of the systems were electrical and no computer modules included. BUT that is probably NOT what the TS wants.

Thanks for looking MisterBill2. Unfortunately I do not have the steering column from the donor vehicle which incorporates the key, switch and theft deterrent module. Sounds like I might be hooped and have to go with the Dakota Digital unit. BTW the alternator works however it puts out 14.5V+- constantly.