Wiring advice

[AshM]

I have discovered some badly burnt wiring loom tape covering the earth cables on the Ignition / Starter relay. (S2 FHC 1970)

Having carefully cut back the loom tape it appears that the earth is made up of only a few strands (literally 3) of connecting wires so has probably been overheating to cause the damage?

I need to replace this section of wiring loom (just the earths - all others completely fine). I have found a good site for wire but want to be 100% sure that I purchase the correct product.

Any electrical experts out there who can advice on what to buy - the wires are described variously but include one measure as 7.0A 11.0A 16.5A 15.0A

Thanks

[cactusman]

If it is the starter relay (solenoid) wires they will not be carrying a significant current. 7.0 or 11.0 amp cable would be fine. I would solder in the new piece using heat shrink as appropriate. Don't use the crappy blue/red/yellow crimp joiners. They look naff and are naff.

I am a bit puzzled it is burned though as the relay current is so low it is unlikely to cause heating. You mention it is the ign/starter. Just checking but are you sure it is not the main feed to the starter from the battery? This would be on the positive side and would be little finger thick and would carry a huge current when cranking the engine. Three strands would get very hot...although I would be surprised if your engine cranked. Any chance of posting a picture of the toasty wires?

[MarekH]

It's what you haven't told us that worries me.

If you have fried a ground connection then it suggests that a power connection should have had a similar current on it at some time in the past. The obvious one which won't be is the started motor itself, so the next thing I'd do is look to see whether the engine to chassis grounding strap is present and in good condition or ascertain whether it was ever missing or poorly connected.

In general, the ground wires on one side of an item are sized to reflect the current usage as dictated by the coloured wiring on the other side. The starter motor is the exception to the rule. It has a ~100amp cable running to its positive terminal and no ground wire. The ground comes via a meaty earth strap between the engine block and the chassis.

Also check the alternator is properly grounded.

kind regards
Marek

[cactusman]

Excellent points Marek....

[AshM]

Thanks for feedback guys; appreciated as always.

Firstly, I used an incorrect term so may have slightly confused. It's the Alternator / Ignition relay (not Ignition / Starter).

The burnt our wire is one of the two wires, connected into a single loop that is earthed to the car by the middle bolt holding the horn and Alternator/ignition relays to the N/S inner wheel arch.

Photo as requested.

fullsizeoutput_12b0.jpeg (228.15 KiB) Viewed 3747 times

Based on your advice I will re-wire with 11A wire.

Chers
Ash

[cactusman]

Hmmm....hard to know but that looks quite a thick piece. I would be on the safe side and go for 17 amp....and as Marek says do make sure the earth strap from the engine block to the chassis is missing or broken.....

[cactusman]

The vital word "not" is obviously missing from my last post

[MarekH]

Dear Ash,

You probably want to take a look as to where the burnt out black wire goes to, i.e. the other end not the earth connection to the chassis bolt.

(The horn also is a very high current device. If it stuck "on" then this might explain the result.)

kind regards
Marek

[AshM]

Thanks both - will follow up on those additional pieces of advice.