V8 Conversion into 24 Volt Vehicle

Table of Contents

You may want to use a V8 in your 24v MQ. Items on the new engine such as chokes, coils and starter motors will be 12v units, which poses a few problems and solutions.

How To

It is possible to run 12v items, and hence a 12v motor, within a 24v vehicle, as explained on this wiki page. If you wish to proceed this way, it will be necessary to use 2 separate relays to control the motor;

  1. Connected to the 24v ignition circuit, to control the coil etc.
  2. Connected to the 24v starter wire, to control the starter motor.

The 24v alternator will need to be adapted (ie new brackets) to the engine you are using. The diesel alternators also have a vacuum pump on the back of the alternator, to run the brake booster. This can either be removed (leaves part of the alternator shaft exposed) or it could be maintained. V8’s with lumpy cams often have bad vacuum, and this could overcome that problem.

Problems Keeping 24v

Using a V8 in a 24v vehicle as indicated above is pointless for a few reasons;

  • The motor does not benefit from the extra voltage.
  • Having 2 batteries in the vehicle introduces extra ‘points of failure’.
  • The second battery could be better utilised as a backup battery.

How to Change to 12v

With the above taken into consideration, you may decide to convert the entire vehicle to 12v. This can be achieved in 2 ways;

  • Source a factory 12v wiring loom and parts for conversion into your vehicle. Either a petrol or diesel loom will suffice, as both will need minor engine-bay modifications to suit.
  • Modify the 24v wiring loom to suit 12v. You will also need to replace the 24v vehicle components (wipers etc). Please refer to this wiki page for additional information on what is required to convert a 24v vehicle.

How to Modify the Loom

Whilst modifying the loom will solve all starting, charging and running issues, you will NOT be able to use the other 24v parts in the vehicle, such as the wipers. 12v replacements will have to be sourced, as mentioned above.

The following link contains a basic writeup on the conversion. A copy of the post is below for safe-keeping.


my mate purchased a former 24v diesel with a 253 in it.

the people that done the conversion retained the 24v system and alternator for the cars electrics and had hooked the starter, coil, fuel pump and thermo fan to 12v, which they took from the drivers side battery (PS- factory wiring takes its 12v from driver side battery as well for the radio and cig lighter. the 24v comes from the passenger side battery as explained by V8Patrol). All the 12v things were turned on via relays, which were hooked to a switch on the dash (like a kill switch, but they hadn’t been hooked to the key at all). the relays were located on the passenger side, between the battery tray and the firewall, exposed in the open. they also ran one of those redarc equalisers to fix the batterys. all the diesel stuff behind the drivers side battery tray was still there as well. he had bulk trouble with this, batterys were always going flat, then the alternator died, was all a bit dodge but it was working. i wouldn’t recommend doing it this way.

then he started talking about putting in subs and amps and stuff, so i convinced him to fix it and make the whole car 12v, we done it in one arvo, easy as. first we decided to use the drivers side battery, because that way there would be less wiring running around the car. we also decided to ditch the second battery all together at this stage, as it was dead anyway and he didnt want to spend money getting a new battery or a dual battery system. so first point of attack was un-tapping all the wiring in the engine bay. then we pulled out all the relays and the redarc that had been added, which left us with the stock loom. we started at the alternator and ripped out all the wires which were ‘useless’. this turned out to be most. FYI, the factory wiring all comes out of the drivers side of the firewall and runs around the front of the car to the passenger battery. so all the fuseable links that went to the passenger side battery stretched around the car already, so we cut all these back and hooked them up (with links) to the drivers side battery. All the wiring that went to the voltage regulator was removed (little module on passenger side near the headlight). then we removed to all the diesel components behind the battery cover on the drivers side. pretty much every wire came out here. the glow plug relay also hooks up to the battery, so this was removed. some of these wires go into the car, so we attached that part of the loom as well. next we removed the 12v accessory relay that is near the drivers side headlight. you can trace this back to the internal fuse block, we chopped it back and just hooked off the existing 24v accessory circuit. we then put in a new wire for the starter motor, but from memory i think the factory wire goes from the key to the diesel module and then another wire goes module to starter, so you could just link these. also, the power wire to key had some trickery going on, it got its power from somewhere wierd, so we ran a new thick wire to the battery and put a nice big fuse on the end. so that sorted out all the factory wiring. nothing needed doing to the headlights, dash, wipers etc.

we removed the 24v alternator and replaced it with a single wire 12v one. the original conversion had already ran a big fat 100A+ wire from the driver side battery to the starter motor, so we just made up a short wire (fat as well) form the alternator to the starter motor. he replaced all the bulbs in the car and got some second hand sealed 12v headlights for $30. i think you can get them for about this price new as well (for 1, not 2 though). he still needs to replace the wiper motor, this works on 12v but it is a bit slow. he’s not fussed atm, because it is summer. the car didnt have aircon and the original people didnt hook up the heater pipes (and he cbf as well) so we just ripped out the whole heater unit. gives heaps more leg room. only problem is he doesnt have a demister now, but i recommonded him this, which I run in my commodore because i ripped the heater unit out of it as well. http://www.calaisturbo.com.au/showthrea … 563&page=3 - post 69 in particular

then we knocked up the wiring for the relays for all the petrol stuff. we hid these behind the battery cover where the diesel stuff was, this way it was shielded etc. to do this, we ran a big fat wire from the battery down through the side hole and connected this to a fuse block. we used a separate fuse for each petrol thing, which fed a separate relay. we could have ran a single relay and fed that straight from the battery, but we decided not to. a standard relay is like 30A, which would be fine for running a fuel pump, coil and the small davies craig thermo fan he had at the time. he was however shopping for some falcon thermo fans. I have these in my commodore and hooked each fan on its own 20A fuse, because apparently they are rated in the mid teens each (so i was told at the time). so if running these, it may have been too much for the 30A fuse. if you were running the mechanical fan, I would probably just go the 1 relay, keep it simple. anyway, we ran a wire from the ignition of the key to signal the relays. this was just linked from one relay to the next. we did the same thing with the earth as well and just hooked this into a wire that was already near by in the stock loom. We had a small mishap at this stage, I was not aware but there is actually 2 ignition ‘circuits’ on the key barrel. They are both on when the key is at ‘run’, but when you turn the key to start, one of them turns off. and of course we hooked to this one. so when we were testing all our fresh circuits, we turned the key to run and were pretty pleased when everything was pumping and spinning as it should straight away. then we cranked it over and it spun but did not run. we were pretty devo, but worked it out quickly.

so anyway, jist of my writing is just convert it to 12v properly. its heaps easier for everything, any accessories he hooks up now, he doesnt have to worry about where he is getting power from etc, or batterys dyeing when you in the bush.