wiring harness

[seniorchristo]

I see on my early Plus 2 there are a number of circuits which are ignition controlled by one single white wire from the ignition switch to the fuse box. Would it make sense to run the white wire to a relay which then using a larger wire could supply more amperage safely? I would like to add separate fused circuits for a music amplifier, fuel pump, driving lights etc..

[seniorchristo]

Any thoughts on this subject?

[Craven]

If you give some idea of the total load you are expecting ( in amps ) a recommendation could be given, I feel the ignition switch itself may be a weak link. A relay would mitigate this if the feed comes from battery directly and switched on by the ignition switch but here you are into an almost new fused supply.

[Andy8421]

Wiring on the original Elan was IMO unsafe. An inflammable car, only two fuses, multiple unfused circuits and ancillaries repurposed from cars with an earth return adapted with a spider's web of earth cables.

Later Plus2s had more fuses, with (I believe) the last of the line Plus2s having 12 fuses.

Irrespective of the model, If I was adding additional equipment (particularly audio equipment that would benefit from a 'clean' supply) then a separate fused supply taken from the starter solenoid via a relay activated by the ignition switch would be a good approach. Make sure you size the cable, connectors and fusing correctly, fuses should blow well before the wire or relay is at its rated limit.

[stugilmour]

I did it similar to what Andy has outlined. Note my loom is non-stock. Basically I figure the ignition switch is robust enough to handle normal loads, but not so good where a clean 12 v source may be required or where we are stretching the original design with various accessories.

The main ignition key White (hot in run & start, unfused) runs to a crimped bus that powers the ignition and two fuses for the Green (hot in run & start, fused) circuits including wipers, heater fan, etc. I also powered the fuel pump off of one of these fuses, but think it would have been preferable to have a separate fuse and maybe even a relay.

The audio stuff is powered from the accessory terminal on the ignition key with Red/White (hot in run, start, & accessory, unfused). For ease of installation/modification I used an inline fuse and an accessory bus that I tucked up on the driver’s side kick panel to power things like a USB plug, a Garmin unit, additional cigar power point, etc. If I were doing the loom design again I would integrate into the fuse box, which in my case is in the glove box.

As Andy described, I used a relay located in the boot to control a large Kenwood amplifier. This relay can generally be triggered by your modern head unit, typically by a Blue wire in the head unit loom that may be labeled as an amp or antenna trigger. The amp power uses a huge flexible battery cable and a screwed-in-place inline fusible link. Most of the stuff required is contained in a generic amplifier installation kit.

My head unit is a bit unusual, with the major module located in the boot beside the amp, so connection between the head unit and amp are all in the boot and the amp sees clean power directly from the positive battery post. The main point here is using the audio loom to trigger the amp relay avoids running an unfused White all the way through the car to the boot, which I figured should be avoided. In a more conventional setup the head unit can be powered from the fused dash accessory bus mentioned above and the supplied long Blue trigger will take care of the amp.

I am presently modifying the setup a bit to install a No-Diz ignition ECU. I am just figuring this out, but the overall idea is to use the existing ignition unfused White as a relay trigger and use clean power from the main solenoid positive post to power the ECU. I figure the coil pack will be fine powered directly by the existing unfused White, similar to the stock ignition coil. Of course, the No-Diz loom has separate light trigger wires between the ECU and the coil pack that see the clean voltage supply.

I should note that both the proposed No-Diz and the existing aftermarket distributor based ignition provide separate tach signal outputs that directly connect to the modified tachometer; the tach needed modification to work with a previously installed Pertronix. Kind of a separate issue, but the broader point is to consider your tach signal if you are fiddling with the ignition wiring.

Anyway, this all might be a bit rambling and specific to my car, but hopefully gives you some ideas. My car started as a Two Fuse Federal model, so perhaps pretty similar to your earlier car. Let us know how you proceed. I support your quest for loud tunes in your Plus 2!

[gus]

TO my knowledge, the only significant fire issue is bad generator control boxes. If you have a generator with an original mechanical control box, they can fail closed[IOW the low voltage control fails to drop out when you shut the car off] When this happens the generator is trying to act as a motor. If your belt is tight enough and your battery is charged enough it will heat up and set the car alight.

I would not keep a generator on a bet.

Once you change to an alternator with an adequate wire to the solenoid, you are usually safe from 'fire'

I do not prefer added complexity, so if you are going to add more load, perhaps an additional fuse for that load.

The real failings of the wiring harness are inadequate wire size for heavier loads[windows] and to some extent the wipers.

Mind you I rewired my entire car with better wire and 14AWG wires to the windows[power and ground] in addition to a fuse for each window, and it has been more or less flawless for nearly 30 years
The last iteration of Plus Two had four fuses[with a few circuit breaker type things]

There is nothing inherently wrong with the plan of adding a relay, but it adds complexity in a way that makes it difficult to troubleshoot in the future.